Glossary
Flight Simulator terms explained
abeam
A relative location approximately at right angles to the longitudinal axis of
the aircraft. An object beside an aircraft is said to be abeam of it.
accelerated stall
A stall induced by turns, pull-ups, or other maneuvers that increase the load
factor (G-load) on an airplane. The loads imposed by such maneuvers typically
increase the speed at which a wing stalls, but they do not affect the angle of
attack at which the stall occurs. That angle, the critical angle of attack, is
always the same.
ace
A military pilot who has destroyed at least five enemy aircraft. The term
originated in France during World War I, where it was given only to top pilots
who had downed at least 10 aircraft. Later, "ace" was commonly used
for any pilot who claimed at least five aircraft. German aces in World War I
were called Kanone ("cannons").
active runway
The runway currently in use for takeoffs and landings. Many large airports have
more than one runway, usually arranged in a pattern to take advantage of
prevailing winds. Some airports have parallel runways to accommodate more
takeoffs and landings. Under specific conditions at airports with operating air
traffic control towers, aircraft may also use intersecting runways for takeoffs
and landings to expedite the traffic flow.
advection
The horizontal movement of air or atmospheric properties. In meteorology, this
process is sometimes referred to as the horizontal component of convection.
advection fog
Fog resulting from the movement of warm, humid air over cooler ground or water.
Advection fog is most common along coastal areas, although it often develops
deep in continental areas. At sea, it is called "sea fog." Advection
fog deepens as wind speed increases up to about 15 knots. Stronger winds lift
the fog into a layer of low stratus or stratocumulus clouds.
advisory circulars (ACs)
In the United States, nonregulatory information and procedures published by the
FAA. Advisory circulars provide background information and more detail on
subjects not completely outlined in the FARs or AIM. Advisory circulars are
published by the Government Printing Office; many publishers also reprint
important ACs as references for pilots. ACs are arranged in series, designated
by a two- or three-digit number. Those in series 00 cover general subjects. ACs
in the 10 series deal with procedural rules. ACs in the 20 series deal with
aircraft; those in the 60 series cover pilots. ACs in the 70s series deal with
airspace, while 90-series ACs cover air traffic and general operating rules.
Issues related to air carriers (airlines) are covered in 120-series ACs.
aerobatics
Precision maneuvers, such as barrel rolls, loops, hammerhead stalls, spins, and
Cuban eights. Often performed at airshows and competitions, many of these
maneuvers are also part of a military pilot's training and can be used in aerial
combat. In fact, many basic aerobatic maneuvers evolved from air-combat tactics
invented during World War I.
"Aerobatics" is also defined in FAR 91.303, which describes
restrictions on aerobatic flight. In that section, "aerobatic flight"
means "any intentional maneuver involving an abrupt change in an aircraft's
attitude, an abnormal attitude, or abnormal acceleration, not necessary for
normal flight."
aerodrome forecast (TAF)
A concise statement of the expected meteorological conditions at an airport
during a specified period (usually 24 hours). TAFs use the same codes employed
in METAR weather reports. TAFs are scheduled four times daily for 24-hour
periods, beginning at 0000Z, 0600Z, 1200Z, and 1800Z. They contain the following
information: type of report, location, issuance time, valid time, and forecast.
aerodynamics
The study of air in motion, in particular, the interactions between air and
surfaces, such as an aircraft wing. Aerodynamicists--scientists and engineers
who specialize in aerodynamics--use wind tunnels, computer models, and other
tools to design and build aircraft and airfoils.
aeronaut
The pilot or navigator of an airship or balloon. Famous aeronauts include the
Montgolfier brothers, inventors of the hot-air balloon; Henri Giffard, builder
and pilot of the first powered dirigible; and August Piccard, who rode a balloon
into the stratosphere.
Aeronautical Information Manual (AIM)
An official source of information about navigational aids, airport operations,
air traffic control procedures, and other subjects of importance to pilots and
air traffic controllers. Published by the FAA, the AIM is available from many
publishers in printed and electronic formats.
aeronautical sectional chart
A 1:500,000-scale aeronautical map that includes topographical and navigational
information for pilots to use during VFR flight.
aeronautics
The study or science of flight.
aerospace
The study of the science and technology of travel in the space above the earth.
Aerospace includes travel within the atmosphere as well as in space beyond the
earth’s atmosphere.
Aérospatiale
French state-controlled aircraft-manufacturing company formed by the merger of
Sud Aviation and Nord Aviation. Based in Toulouse, Aérospatiale has produced a
wide range of helicopters and was the manufacturer of the supersonic Concorde
airliner.
aerostat
A lighter-than-air craft, such as a hot-air balloon or dirigible, that gets lift
principally from buoyancy instead of generating lift with airfoils.
afterburner
Device that injects fuel into the exhaust stream of a turbojet engine. The
combustion of the unburned oxygen from the exhaust and the jet fuel provides an
extra boost at takeoff or during combat maneuvers. Also known as
"reheat," especially in Great Britain.
AGL
Abbreviation for "above ground level." The height of clouds in airport
weather observations and forecasts is usually reported in AGL.
ailerons
Movable control surfaces, usually located near the wing tips, that control the
rolling motion of an aircraft. The pilot deflects the ailerons by moving the
control yoke or stick left and right. The ailerons move simultaneously in
opposite directions. For example, when the pilot moves the yoke or stick left,
the aileron on the left wing moves up, decreasing the lift on the left wing. At
the same time, the right aileron moves down, increasing the lift on the right
wing. The word derives from the French word aile, meaning "wing."
air mass
In meteorology, an extensive body of air within which the conditions of
temperature and moisture in a horizontal plane are essentially uniform.
air traffic control (ATC)
A network of control towers, approach and departure controls, and Air Route
Traffic Control Centers (ARTCCs) designed to ensure the safe and efficient flow
of air traffic. ATC's primary responsibility is to maintain separation between
aircraft operating under Instrument Flight Rules (IFR), but ATC also provides
services to aircraft operating under Visual Flight Rules (VFR).
ATC's functions are divided into several segments. Ground control supervises aircraft taxiing to and from runways. The tower, or "local control," handles aircraft in the vicinity of an airport, clearing them for takeoff or landing. Departure and approach controls manage the airspace surrounding one or more airports, and en route centers control traffic between airports.
Airbus Industrie
Aircraft manufacturing consortium that includes France's Aérospatiale,
Germany's Deutsche Airbus, British Aerospace, and CASA of Spain. Based in
Toulouse, France, Airbus is the world's second-largest manufacturer of
commercial airplanes (after Boeing). Its major products are the A310, A320,
A321, A330, and A340 airliners.
aircraft
A flying machine. In the United States, the FAA divides aircraft into classes
and categories. With respect to the certification of aircraft, classes are broad
groupings, such as airplanes, rotorcraft, gliders, balloons, landplanes, and
seaplanes. Categories define aircraft based on their intended use or operating
limitations; for example, transport, normal, utility, acrobatic, limited,
experimental, restricted, and provisional. With respect to the certification of
pilots, class means a classification of aircraft with similar operating
characteristics; for example, single engine, multiengine, land, water, and
helicopter. Category means a broad classification of aircraft, such as airplane,
rotorcraft, and glider.
Aircraft Owners and Pilots Association
The world's largest aviation organization, dedicated to making flying safer,
more productive, more affordable, and more fun. AOPA is headquartered in
Frederick, Maryland.
airfoil
A device that interacts with a moving stream of air to produce lift or thrust.
Wings, propellers, tail surfaces, helicopter rotor blades, ailerons and other
control surfaces, and turbine blades are all airfoils.
airframe
From 14 CFR Part 1: "The fuselage, booms, nacelles, cowlings, fairings,
airfoil surfaces (including rotors but excluding propellers and rotating
airfoils of engines), and landing gear of an aircraft and their accessories and
controls."
airline transport pilot certificate (ATP)
In the United States, the pilot certificate required to act as pilot in command
of an aircraft for an air carrier (airline) and for certain other operations.
The ATP is often referred to as "the Ph.D. of aviation." To be
eligible for an ATP certificate, a pilot must be at least 23 years old and hold
a current first-class medical certificate. In general, an ATP applicant must
also have at least 1,500 hours of flight time, including minimum amounts of time
on cross-country flights, flights at night, and instrument flight time.
airship
An engine-driven, lighter-than-air aircraft that can be steered.
airspace
The part of the atmosphere that lies above the surface and is under the
jurisdiction of a nation or controlling authority. In the United States, there
are two categories of airspace: regulatory and nonregulatory. Within those two
categories, there are four types of airspace: controlled, uncontrolled, special
use, and other. Airspace is assigned to one of the types according to the
density and complexity of the air traffic using the airspace, the types of
operations conducted in that airspace, and other factors.
airspeed
The rate at which an aircraft moves through the surrounding air. Pilots use
several types of airspeed during flight. For example, indicated airspeed (IAS)
is the speed shown on the airspeed indicator (usually in knots). Pilots use IAS
to control an aircraft and manage its performance. Calibrated airspeed (CAS) is
IAS corrected for instrument and installation error. True airspeed (TAS) is IAS
corrected for changes in atmospheric temperature and pressure. Pilots use TAS to
solve navigation problems.
The aircraft's speed over the ground—ground speed—is TAS corrected for the effect of a headwind or tailwind.
airspeed indicator
The instrument that displays an aircraft's speed relative to the air in which it
is moving. Most modern aircraft have airspeed indicators calibrated in knots or
in Mach number.
altimeter
The indicator that displays an aircraft’s present altitude. It is usually
calibrated to give mean sea level (MSL) altitude. Most altimeters are called
"pressure altimeters" because they measure the decrease in atmospheric
pressure as the aircraft climbs. Because of this, the altimeter must be
calibrated to the local atmospheric pressure to compensate for regional
variations in pressure that would make the readings inaccurate.
altimeter setting
The value to which the scale of a pressure altimeter is set so it reads true
altitude at field elevation. The setting is usually given in inches of mercury
(Hg) or millibars.
altitude
Height of the aircraft above a reference level. Altitude above ground level
(AGL) is the absolute height above the earth. Altitude above mean sea level
(MSL) is the height above the average level of the earth’s oceans.
altocumulus
White or gray layers or patches of middle clouds, often with a waved appearance.
Altocumulus clouds appear as rounded masses or rolls. They are composed mostly
of liquid water droplets which may be supercooled. At subfreezing temperatures,
altocumulus clouds may contain ice crystals.
altocumulus castellanus
A type of middle cloud that includes some vertically developed, cumuliform
protuberances (some of which are taller than they are wide, as castles). These
cumuliform sections give the cloud a crenelated or turreted appearance that is
especially evident when seen from the side. This cloud indicates instability and
turbulence at the altitudes where it appears.
altostratus
Stratiform—flat, layered—clouds that form in the middle altitudes. The
height of their bases ranges from 6,500 to 23,000 feet (1,980 to 7,000 meters)
in middle latitudes.
anemometer
An instrument for measuring wind speed.
aneroid barometer
A barometer that operates on the principle of changing atmospheric pressure
bending a metallic surface, which, in turn, moves a pointer across a scale
graduated in units of pressure.
angle of attack
The angle between the wing and the oncoming airflow—the relative wind. It's
important to understand that the angle of attack is related to the direction in
which an aircraft is moving, not to the angle the wing makes with the horizon.
In general, as angle of attack increases, so does the amount of lift a wing
produces. However, at a specific point, called the "critical angle of
attack," the air flowing over a wing can no longer follow the airfoil's
contour, and it becomes turbulent. The sudden loss of lift at this point is
called a "stall."
angle of incidence
The angle at which a wing or propeller blade is mounted to the aircraft fuselage
or to the propeller hub. The pilot cannot control the angle of incidence.
anticyclone
An area of high atmospheric pressure with a closed anticyclonic circulation.
Viewed from above, the circulation is clockwise in the Northern Hemisphere,
counterclockwise in the Southern Hemisphere, and undefined at the equator.
antitorque pedals
Pedals in a helicopter that control the tail rotor speed to compensate for the
torque of the main rotor. Antitorque pedals are used to maintain coordinated
flight.
anvil cloud
Popular name given to the top portion of a cumulonimbus (thunderstorm) cloud
that has an anvil-like appearance.
approach
The phase of flight just prior to touchdown during landing. It is important that
airspeed and attitude be stabilized during approach.
approach attitude
The aircraft’s longitudinal axis angle with respect to the horizon when making
a landing approach.
approach lighting system (ALS)
Color-coded or sequenced flashing lights that clearly define the approaches to a
runway. The ALS helps pilots make the transition to visual references at the end
of an instrument approach. It can also aid pilots operating at night under
visual flight rules (VFR).
area forecast (FA)
In the United States, a forecast of general weather conditions over an area the
size of several states. It is used to forecast en route weather and to
interpolate conditions at airports that do not issue terminal forecasts. FAs are
issued three times a day by the National Aviation Weather Advisory Unit (NAWAU)
in Kansas City, Missouri, for each of six areas in the contiguous 48 United
States. Other offices issue reports for Alaska, Hawaii, and the Gulf of Mexico.
An area forecast contains a 12-hour specific forecast, followed by a 6-hour (18-hour in Alaska) categorical outlook, giving a total forecast period of 18 hours. The information in an FA includes several parts, including a synopsis, VFR clouds and weather, and other items of significance to VFR flight, including thunderstorms and strong winds, if forecast.
area rule
An aeronautical engineering principle that helps designers reduce drag at speeds
near the speed of sound. Pinching in the fuselage where it meets the canopy,
tail, or wings—creating the so-called Coke-bottle effect—cuts drag
dramatically, reducing the amount of power an aircraft needs to reach supersonic
speeds.
Aresti notation
A system of "aerocryptographics" for pilots and judges at aerobatic
competitions and airshows. Named for José Louis Aresti, a Spanish aerobatic
pilot who devised the notation system and built a dictionary of maneuvers and
sequences.
artificial horizon
See attitude indicator.
aspect ratio
The ratio between the length (span) and width (chord) of a wing. In general, a
wing with a high aspect ratio is more efficient than a wing with a smaller
aspect ratio.
atmospheric pressure
The pressure exerted by the air on the earth and everything on it. This is
measured in inches (or millibars) of mercury on an instrument called a
barometer. Thus, the term "barometric pressure" is frequently
interchanged with atmospheric pressure. Typically, the pressure measures between
28 and 32 inches of mercury at sea level, decreasing at higher elevations. See
also barometer.
attitude
The aircraft’s position around its axis.
attitude flying
Flying based on an aircraft’s attitude (orientation to the world around it).
attitude indicator (artificial horizon)
The instrument that shows the aircraft's pitch and bank attitudes with respect
to the ground. Pilots use the attitude indicator, sometimes called the
"artificial horizon," when the true horizon isn't visible.
autocoordination
In Flight Simulator, an option that automatically synchronizes the actions of
the ailerons and rudder to maintain coordinated, that is, balanced, flight,
especially during turns. You can turn autorudder on or off by choosing the
Realism Settings command from the Aircraft menu.
autogyro
An engine-powered aircraft that uses a propeller for forward motion and a large,
free-rotating, horizontal rotor for lift. Also spelled "autogiro."
automatic direction finder (ADF)
A radio navigation instrument that receives signals from nondirectional radio
beacons (NDBs) or AM radio stations. The needle on the ADF indicator always
points toward the selected radio signal. A pilot can determine the magnetic
bearing to the station by using the formula, Relative Bearing + Magnetic Heading
= Magnetic Bearing.
automatic pilot (autopilot)
A device that automatically controls an aircraft. Similar in concept to the
cruise control feature on an automobile, simple autopilots keep an airplane's
wings level. More sophisticated autopilots can fly an airplane from immediately
after takeoff all the way to its destination and then make an automatic landing.
Autopilots use gyros and other sensors to keep track of the airplane's altitude,
speed, and position, and then send signals to the appropriate controls to keep
the airplane on course and altitude.
automatic terminal information service (ATIS)
A continuous-loop recording played over a specified frequency that gives pilots
the current weather, runway or runways in use, and other airport information.
ATIS is available at many airports with an operating control tower. The tape is
updated hourly or whenever there is a significant change in weather or airport
information. Each update is labeled with a letter of the alphabet, which is
pronounced according to the ICAO standard. For example, the broadcast at 11:00
a.m. might be designated "Information Delta"; the next update would be
designated "Information Echo." Pilots are expected to listen to the
ATIS and indicate that they have received the current information before they
make initial contact with air traffic controllers.
autorotation
The descent of a helicopter without power being applied to its rotor.
Aerodynamic forces cause the rotor to spin.
autothrottle
In addition to an autopilot, Flight Simulator jets are equipped with an
auothrottle that can control airspeed automatically . The autothrottle works
independently from the autopilot, although most autothrottle controls are
presented on the mode control panel (MCP) along with the autopilot controls.
avgas
Grades of gasoline approved for use in aircraft.
avionics
Derived from "aviation electronics," this term most commonly refers to
the electronic communication, navigation, and flight-control equipment on board
an aircraft.
axial flow
Flow of air in a path parallel to the center. In an axial-flow turbine engine,
air enters the front and follows a straight path through a series of turbine
blades that compress the air before it enters the combustion chamber.
axis indicator
In Flight Simulator, a display that shows the current axis of the aircraft and
gives a good indication of where the aircraft's center is pointing. You can turn
the axis indicator on and off or change its shape by choosing View Options from
the Views menu, and then choosing an Axis Indicator option.
azimuth
Angular measurement made in a horizontal plane and in a clockwise direction from
a fixed reference direction to an object. Two points on adjacent legs that both
extend from the same right angle are said to be 90 degrees in azimuth from one
another.
balloon (verb)
To increase the pitch attitude and angle of attack too rapidly. Ballooning can
lead to a low-altitude stall, a hard landing, or porpoising if a tricycle-gear
airplane lands nose-wheel first.
bank
The angle of an airplane's wings with respect to horizon; rotation about an
aircraft's longitudinal axis. Pilots control bank using the ailerons. Airplanes
turn principally because banking the wings creates a horizontal component of
lift. Pilots measure bank in degrees.
barnstormer
A pilot who tours the countryside, performing at exhibitions and taking
passengers on sightseeing flights.
barometer
An instrument for measuring the pressure of the atmosphere. The two most common
types are mercurial and aneroid.
barometric altimeter
A barometer that measures altitude by registering changes in atmospheric
pressure as an aircraft climbs or descends. Large aircraft often are also
equipped with a radio altimeter that measures the height of an aircraft by
sending a radio beam to the ground and converting the time it takes to return
into height above the surface. Radio altimeters are particularly useful during
instrument approaches.
barometric pressure
See atmospheric pressure.
base leg
The leg flown in a standard left or right traffic pattern that is at right
angles to both the downwind and final approach legs and is parallel to the
threshold of the runway.
bearing
The horizontal direction to one object from another. An example would be the
horizontal direction to a navigation transmitter from an aircraft.
Beech, Walter
1891–1950. American aircraft manufacturer. In 1932, Beech and his wife, Olive
Ann, founded Beech Aircraft, which became a leading producer of light airplanes.
Earlier in his aviation career, Beech was a salesman and test pilot for the
Swallow Airplane Company. Failing to persuade the company to adopt metal
airframes, he quit and teamed up with Clyde Cessna and Lloyd Stearman to form
the Travel Air Manufacturing Company, of which Beech was president.
Bell, Alexander Graham
1847–1922. Scottish-born American inventor. Bell's early experience in
teaching deaf students led to an interest in communications. By 1875, he was an
expert in electric wave transmission, and the following year, he invented the
telephone. In 1892, Bell became interested in aviation. He experimented with
kites, photographed Samuel Langley's successful launch of the model Aerodrome,
and later formed the Aerial Experiment Association with a group of young
aviators that included Glenn Curtiss.
Bernoulli, Daniel
1700–1782. Swiss scientist. His most important discovery, known as
"Bernoulli's principle," states that the total energy of fluid in
motion remains constant: If its speed increases, its pressure decreases; if its
speed decreases, its pressure increases. This principle was important to early
scientists studying airflow, and their applications led to the design of wings
capable of lifting heavier-than-air craft off the ground.
Bernoulli's principle
The physical law stating that the total energy of fluid in motion remains
constant: if its speed increases, its pressure drops; if its speed decreases,
its pressure increases. Wings are designed to exploit this relationship by
accelerating air that passes over their curved upper surfaces, thereby
decreasing its pressure. The difference between the lower pressure above a
moving airfoil and the relatively higher pressure below creates lift. This
principle was first established by the Swiss scientist Daniel Bernoulli
(1700–1782). Although aeronautical engineers continue to debate the theory of
how lift is created, Bernoulli's principle is still regarded as a fundamental
explanation of how airfoils produce lift.
biplane
An airplane equipped with two pairs of wings, usually one above and one below
the fuselage. Early-model biplanes had their wings connected to each other with
struts and wires. Modern biplanes are most often used for aerobatic flying.
bleed off
To decrease airspeed or altitude in a slow, carefully controlled manner.
blimp
A nonrigid airship generally shaped like a cigar. Internal gas pressure
maintains both the blimp's buoyancy and its shape. There are many theories as to
the term's origin—one of the most popular states that "blimp" is the
sound made if you plunk the envelope with your finger.
Boeing
American aircraft company, founded by William Boeing in 1916, and today, the
world's largest manufacturer of commercial airplanes. Boeing also produces
military aircraft and spacecraft, but it is best known for its "7"
series of passenger jetliners—the 707, 727, 737, 747, 757, 767, and 777.
booster
See performance booster.
buffet
Vibration, usually affecting the horizontal stabilizer and elevator, caused by
turbulent airflow. Buffet occurs as the wing approaches its critical angle of
attack and the smooth flow of air over the top surface of the wing becomes
turbulent, like water flowing over rocks. This turbulent air strikes the
airplane's tail surfaces and induces a mild vibration that the pilot feels
through the flight controls. Pilots use the onset of buffeting as one indication
of an impending stall.
Buys Ballot's law
The law that states that if an observer in the Northern Hemisphere stands with
his or her back to the wind, lower pressure is to the left.
cache
See disk cache.
calibrated airspeed (CAS)
Indicated airspeed (IAS) corrected for instrument and installation error. The
position of the pitot tube and static ports, flap setting, and pitch attitude of
an aircraft can affect the accuracy of the airspeed indicator—especially at
the low end of an airplane's speed range. Aircraft operating handbooks and
placards on the instrument panel often include a table to help pilots determine
CAS.
call sign
The identification that ATC and a pilot use for a particular flight or aircraft.
Call signs are generally a combination of the aircraft type or manufacturer and
the aircraft registration for civilian planes, a combination of the airline and
flight number for airline flights, and a combination of branch of service and
flight number for military flights. Call signs should always be included in any
communication with ATC to avoid confusion about who’s talking.
canard
A horizontal surface, mounted in front of an aircraft's main wing, that serves
as a stabilizer to control pitch. Canards also reduce drag by cutting down the
force generated by a conventional tail. Canards were first used in the
pioneering days of aviation, and today, their principle advantage in modern
design is in preventing deep stalls. The canard is designed to stall before the
main wing, lowering the angle of attack of the main wing before that wing can
stall. The term "canard" is also used to describe any aircraft that
flies tail first.
canopy
A transparent enclosure that covers an aircraft cockpit. Modern canopies are
formed from a single piece of transparent plastic.
canted gyroscope
A gyroscope within a flight instrument, usually the turn coordinator, with its
rotational axis tilted, or canted, with respect to the aircraft's longitudinal
axis. The tilted axis causes the gyro to respond to a banking or yawing motion.
cantilever wing
A wing attached to the fuselage without external struts or wire bracing.
carburetor icing
Because of the effect of vaporizing fuel and the decrease in pressure in the
carburetor’s venturi, ice can form in the carburetor throat with the presence
of moisture in the air. This can occur even on warm days with temperatures as
high as 100 F (38 C), but is more likely when temperatures are below 70 F (21 C)
and the relative humidity is above 80 percent.
carburetor
The part of a piston engine that mixes fuel and air, creating a combustible
mixture that is ignited and burned in the cylinders. Filtered air enters the
carburetor through a venturi, a narrow throat. As the air flows through the
venturi, its velocity increases. The air pressure drops, creating a partial
vacuum that draws in fuel through a needle valve. The fuel, atomized into tiny
drops, mixes with the air, and the mixture flows into the intake manifold, a
tube with branches that delivers the mixture to each cylinder.
category (aircraft)
In the United States, with respect to the certification of aircraft, a grouping
based on intended use or operating limitations. In the United States, all
aircraft are certified in a specific category. Examples include: transport,
normal, utility, acrobatic, limited, restricted, and provisional. With respect
to pilot certification, category refers to a broad classification of aircraft,
such as airplane, rotorcraft, and glider.
ceiling
The height above the earth's surface of the lowest layer of clouds or obscuring
phenomena that is reported as "broken" or "overcast." The
height of the ceiling is one of the factors that determines whether flight under
visual flight rules (VFR) is possible. In the United States, the ceiling
generally must be at least 1,000 feet (305 meters) for operations under VFR in
controlled airspace.
ceilometer
A cloud-height measuring system. It projects light on the cloud, detects the
reflection by a photoelectric cell, and determines height by triangulation.
cell
Another name for a thunderstorm or cumulonimbus cloud. Pilots, air traffic
controllers, and meteorologists often use this term to report areas of intense
precipitation, lightning, or turbulence associated with a thunderstorm.
center of gravity (CG)
The point at which an airplane would balance if it were suspended by a cable.
The CG is also the point at which the three axes—longitudinal, lateral, and
vertical—of an airplane intersect and the point at which the four fundamental
forces of flight—lift, weight, thrust, and drag—are assumed to act.
Pilots must ensure that the CG of a loaded aircraft falls within a specified
range, called the "CG envelope." If the CG is outside the envelope,
the aircraft may be difficult or impossible to control. To determine the
position of the CG, divide total aircraft movement by total weight.
centerline
A painted line running along the center of a runway (or taxiway) that divides it
into two sections.
centrifugal flow
Flow of air outward from the center of rotation. Early turbine engines used the
principle of centrifugal flow to compress air before it entered the combustion
chamber.
centrifugal force
The force that tends to impel an object outward from the center of rotation.
Certified Flight Instructor
An individual certified by a country’s aviation authority to provide flight
instruction.
certified flight instructor certificate
In the United States, a certificate that allows a person to give instruction to
applicants for other pilot certificates. To be eligible for a certified flight
instructor (CFI) certificate, a person must be at least 18 years old and hold a
current second-class medical certificate and a commercial pilot certificate. The
applicant must demonstrate proficiency in teaching and in demonstrating the
maneuvers required for various pilot certificates. A CFI certificate must be
renewed every 24 months.
Cessna Aircraft Company
American manufacturer of aircraft founded in 1927 by Clyde Cessna. Production of
the Cessna "A" series began in 1928, but the Great Depression brought
business to a near standstill. However, the success of civil and military
versions of the T-50 "Bamboo Bomber" created a wartime boom for Cessna
that helped the company later produce more aircraft than any other manufacturer.
Cessna, Clyde
1880–1954. American aviation pioneer and aircraft manufacturer. Inspired by
the Moisant International Aviators' air circus, Cessna built his own monoplane
and became a barnstormer. Later, he teamed up with Walter Beech and Lloyd
Stearman in the Travel Air Manufacturing Company before forming the Cessna
Aircraft Company in 1927. Cessna retired in 1935, handing the reins to his
nephew, Dwane Wallace.
checklist
A procedure list used by pilots to systematically check and set an aircraft’s
systems prior to takeoff and landing and during emergencies.
checkride
A flight administered by an examiner from a country’s aviation authority to
test an individual before issuing a pilot certificate to that individual.
chord
Also called the "chord line," an imaginary line drawn in cross-section
from the leading edge to the trailing edge of a wing. The chord line is the
reference used to determine the angle of attack and to draw lift, weight, and
other vectors when analyzing a wing that is producing lift.
cirriform
Clouds composed mostly or entirely of small ice crystals, usually transparent
and white, often producing halo phenomena not observed with other cloud forms.
Cirriform clouds include cirrus, cirrocumulus, and cirrostratus clouds. The
average height of cirriform clouds ranges upward from about 20,000 feet (6,096
meters) in the middle latitudes.
cirrocumulus
A cirriform cloud appearing as a thin sheet of small white puffs resembling
flakes or patches of cotton without shadows; sometimes confused with
altocumulus.
cirrostratus
A cirriform cloud appearing as a whitish veil, usually fibrous, sometimes
smooth. Cirrostratus clouds often produce halo phenomena and may totally cover
the sky.
cirrus clouds
Feathery, high-altitude clouds composed of ice crystals. Cirrus clouds typically
form in shallow, scattered-to-broken layers on the equatorial side of the jet
stream when high-level moisture is available. They indicate strong upper winds.
Cirrus clouds do not in themselves constitute a hazard to aircraft, but they
should alert pilots to the possibility of high-altitude turbulence and the
approach of developing or intense weather systems.
class
With respect to the certification of aircraft, this is a broad grouping of
aircraft with similar characteristics of propulsion, flight, or landing. In the
United States, the FAA recognizes the following classes of aircraft: airplanes,
rotorcraft, gliders, balloons, landplanes, and seaplanes.
With respect to the certification of pilots, this is a grouping of aircraft with similar operating characteristics; for example, single engine, multiengine, land, water, and helicopter.
Class A airspace
In the United States, the airspace extending from 18,000 feet (5,486 meters)
above mean sea level up to and including Flight Level 600 (approximately 60,000
feet [18,288 meters]). Formerly known as "positive control airspace (PCA)."
All operations in Class A airspace are conducted according to instrument flight
rules (IFR) under direct air traffic control. Class A airspace is not marked on
aeronautical charts.
Class B airspace
In the United States, the airspace around the busiest major terminals. Formerly
called a "terminal control area (TCA)," Class B airspace is typically
arranged in rings centered on the primary airport. The innermost ring usually
extends from the surface up to 10,000 feet (3,050 meters). The next rings each
begin at different intermediate altitudes to allow nonairline traffic to transit
the area beneath the Class B airspace and operate at satellite airports. This
stair-step arrangement, drawn in cross-section, makes Class B airspace look like
an inverted wedding cake.
All aircraft operating in Class B airspace must receive a clearance from air traffic control, regardless of current weather conditions. Aircraft must also have a transponder with automatic altitude-reporting capability. The boundaries of Class B airspace are marked with solid blue lines on United States aeronautical charts.
Class C airspace
In the United States, the airspace around airports that have an operating air
traffic control tower, radar approach control, and a high level of IFR
operations or airline traffic. Class C airspace is typically designated around
second-tier airports that are not as busy as major terminals. Many military
airports are also surrounded by Class C airspace.
Class C airspace is typically arranged in two rings centered around the primary airport. The innermost ring, with a typical diameter of 5 nautical miles (nm), generally extends from the surface up to 4,000 feet (1,220 meters). The next ring begins at 5 nm from the center and extends to 10 nm. It begins at 1,200 feet (365 meters) above the airport elevation and extends to 4,000 feet (1,220 meters). Class C airspace also includes an outer area, which extends to 20 nm from the primary airport
All aircraft operating in Class C airspace must establish communications with air traffic control, regardless of current weather conditions. Aircraft must also have a transponder with automatic altitude-reporting capability (Mode C). The boundaries of Class C airspace are marked with solid red lines on United States aeronautical charts.
Class D airspace
In the United States, the airspace around an airport that has an operating air
traffic control tower. Class D airspace is typically a circle centered on the
airport with a diameter of about 5 cm. It typically extends from the surface to
2,500 feet (762 meters) above the airport elevation. Class D airspace often
includes extensions to ensure that the controlled airspace encloses instrument
approaches.
All aircraft operating in Class D airspace must establish communications with the air traffic control tower, regardless of current weather conditions. The boundaries of Class D airspace are marked with dashed blue lines on United States aeronautical charts.
Class E airspace
Generally, in the United States, controlled airspace not designated as Class A,
B, C, or D. Class E airspace includes low-altitude airways, extensions to Class
D airspace, transition areas, and other airspace where air traffic control
clearances are required when the ceiling and visibility do not meet the minimums
for operations under visual flight rules (VFR).
Class E airspace typically begins at either 700 feet (213 meters) or 1,200 feet (365 meters) above the surface. It extends upward to the base of any overlying controlled airspace. When designated as an extension to Class D airspace, Class E airspace begins at the surface. Aircraft operating in Class E airspace must establish communications with the air traffic control tower only when operating under instrument flight rules (IFR). The boundaries of Class E airspace are marked with dashed red lines or with shaded red or blue lines on United States aeronautical charts.
Class G airspace
In the United States, airspace not designated as Class A, Class B, Class C,
Class D, or Class E airspace. Class G airspace typically begins at the surface
and extends upward to either 700 feet (213 meters) or 1,200 feet (365 meters)
above ground level (AGL). The boundaries of Class G airspace are not explicitly
marked on United States aeronautical charts.
clear ice
Relatively transparent ice with a homogeneous structure and few, small air
spaces. Clear ice is usually associated with large, supercooled water drops
typically found in cumuliform clouds. Clear ice forms when the liquid portion of
a drop flows out over the aircraft surface before it freezes. Clear ice is hard,
heavy, and difficult to remove.
clear-air turbulence (CAT)
Turbulence in an area where no clouds are present; in particular, turbulence at
high altitudes. CAT is also sometimes used to describe turbulence associated
with wispy cirrus clouds. Many phenomena can generate CAT, but it is often
associated with the jet stream, especially in winter, when temperature contrast
is greatest between cold and warm air. CAT also occurs in wind shears associated
with sharply curved contours of strong lows, troughs, and ridges aloft, mountain
waves, and areas of strong cold or warm air advection.
climbout
That portion of a flight between takeoff and the initial cruising altitude.
cloud layer
In Flight Simulator, a user-specified weather option that includes the type of
cloud, the heights of the bases and tops of the clouds, visibility, turbulence,
and whether icing conditions exist. You select these options in the Advanced
Weather dialog box. You can create two cloud layers in each weather area.
col
In meteorology, the neutral area between two highs and two lows or the
intersection of a trough and ridge. The col on a pressure surface is analogous
to a mountain pass on a topographic surface.
cold front
Any non-occluded front that moves in such a way that colder air replaces warmer
air.
collective
(Short for collective pitch control.) A helicopter's primary altitude and power
control. It varies the lift produced by the main rotor system by increasing or
decreasing the pitch of all the main rotor blades simultaneously (that is,
collectively, hence the name of the control).
COM
Abbreviation for "communication"; usually refers to radio
communication. Aircraft communications radios are typically labeled "COM
1," "COM2," and so forth.
commercial pilot certificate
In the United States, a pilot certificate that allows a person to act as pilot
in command of an aircraft for compensation or hire. To be eligible for a
commercial pilot certificate, a person must be at least 18 years old and hold a
current second-class medical certificate and a private pilot certificate. The
applicant must have at least 250 hours of flight time, including at least 10
hours of instruction in an aircraft with a controllable pitch propeller, flaps,
and retractable landing gear. The applicant also must have at least 50 hours of
cross-country flight time and meet other experience and knowledge standards.
compass rose
A graduated circle painted on a ramp or taxiway to be used by pilots to verify
and compensate a magnetic compass in their aircraft.
composites
Materials consisting of glass or carbon fibers set in a matrix of plastic or
epoxy resin. Composites are increasingly used in the construction of modern
aircraft because they are stronger and lighter than metals. Many new kit-built
and experimental aircraft are built primarily out of composites.
condensation
The change of water vapor to liquid water.
condensation trail
A cloud-like streamer that frequently forms behind aircraft flying in clear,
cold, humid air. Condensation trails are also called "contrails" and
"vapor trails."
contrarotating propellers
A pair of propellers, mounted one behind the other on the same engine, that
rotate in opposite directions. Contrarotating propellers make more efficient use
of the power from the engine and counteract the gyroscopic and aerodynamic
forces generated by a single large propeller turning in one direction. The
principle was first applied to an Italian Macchi-Castoldi racing plane in 1933.
control yoke
The steering-wheel-like control connected to the ailerons and elevator. A pilot
turns the yoke to move the ailerons and bank the wings. The pilot moves the yoke
forward and back to move the elevator, which lowers and raises the nose. Some
airplanes have a stick or "joystick" instead of a control yoke.
controlled airport
An airport with an operating control tower. You must obtain a clearance to take
off or land at a controlled airport and follow the tower controller's
instructions while operating on or around a controlled airport. Controlled
airports are usually located within Class B, Class C, or Class D airspace. The
basic rules for operating at an airport with a control tower are contained in
FARs 91.131, 91.130, and 91.129 and in the Aeronautical Information Manual
(AIM).
controlled airspace
In the United States, airspace in which operations may require a clearance from
air traffic control (ATC), especially when a low ceiling or restricted
visibility requires aircraft to operate under instrument flight rules (IFR).
Controlled airspace is divided into several classes (A, B, C, D, E, and G)
according to standards established by ICAO. Each class has different operating
rules, including requirements for communications with ATC, specific clearances
from ATC, pilot qualifications, aircraft equipment, maximum operating speeds,
and minimum ceiling and visibility for operations under visual flight rules
(VFR).
convection
In meteorology, atmospheric motions that are predominantly vertical, resulting
in vertical transport and mixing of atmospheric properties.
convective clouds
Clouds exhibiting vertical development; cumuliform clouds. Convective clouds
form in air that is moving primarily upward rather than horizontally.
coordinated flight
Flight, especially during turns, in which the horizontal and vertical forces at
work on the airplane are in balance. The inclinometer, part of the turn
coordinator or "needle and ball," shows the pilot whether the aircraft
is in coordinated flight. When the ball moves to the inside of a turn, the
airplane is "slipping"—that is, the angle of bank is too steep for
the rate of turn. If the ball moves to the outside of a turn, the airplane is
"skidding"—that is, the rate of turn is too great for the angle of
bank. Uncoordinated flight can also occur during flight at low airspeed if the
pilot does not apply enough rudder to compensate for the yaw force created by
the propeller and engine at high power settings.
Coordinated Universal Time
See Greenwich Mean Time.
coordinates
The intersection of lines of reference, expressed in degrees, minutes, and
seconds of latitude and longitude, used to determine a position or location.
Coriolis force
A deflective force resulting from the earth's rotation. In the Northern
Hemisphere, the Coriolis force deflects moving air to the right. In the Southern
Hemisphere, the force deflects moving air to the left. The force acts at a right
angle to wind direction and is directly proportional to wind speed. That is, as
wind speed increases, Coriolis force increases. At a given latitude, double the
wind speed, and you double the Coriolis force. Coriolis force also varies with
latitude, from zero at the equator, to a maximum at the poles. It influences
wind direction everywhere except immediately at the equator; but its effects are
most pronounced in middle and high latitudes.
course deviation indicator
A vertical needle on the omnibearing indicator (OBI) that shows your deviation
from the very high frequency omnidirectional range (VOR) radial set by the
course selector. If the needle is to the right of center, the radial lies to the
right of your current position.
course selector
The knob or other control a pilot uses to select a VOR radial. Also known as the
"omnibearing selector (OBS)."
cowling
That removable portion of the airframe of an aircraft that covers the engine.
crab angle
The angle between an aircraft's heading and ground track. This angle is
determined by the crosswind component and the airspeed of the aircraft; the
stronger the crosswind and the lower the airspeed, the larger the aircraft's
crab angle.
critical angle of attack
The angle of attack at which a wing stalls. The critical angle of attack is
determined by the airfoil design. A wing always stalls when it reaches its
critical angle of attack, regardless of the aircraft's airspeed or attitude.
Most general aviation aircraft have wings with a critical angle of attack of
18–20 degrees.
cross-country flight
A flight from one airport to another covering a distance great enough to require
the use of some form of navigation.
crosswind
A wind that is blowing at an angle to the flight path of an aircraft. Pilots
must correct for crosswinds by pointing the nose of the aircraft at some angle
into the wind in order to maintain the desired course across the ground.
cruise speed
The average speed of an aircraft during straight-and-level flight at normal
power settings.
cumuliform
A descriptive term applied to all convective clouds that develop vertically
rather than into horizontally extended stratiform types. Cumuliform clouds
develop in unstable air.
cumulonimbus clouds
Dense, vertical cloud formations that usually produce heavy rain, thunderstorms,
or hailstorms. "Cumulus" is from the Latin for "heap";
"nimbus," for "rain cloud." Like all cumuliform clouds,
cumulonimbus form in unstable air. A cumulonimbus cloud is heavy and dense. It
can have massive towers, often with tops in the shape of an anvil or plume.
Cumulonimbus clouds are often associated with virga, precipitation, and low
ragged clouds (scud), lightning, thunder, and sometimes hail. They occasionally
produce a tornado or a waterspout. Cumulonimbus clouds can extend well into the
stratosphere.
cumulonimbus mamma
A cumulonimbus cloud having hanging protuberances, such as pouches, festoons, or
udders, on the underside of the cloud. It is usually indicative of severe
turbulence.
cumulus clouds
Fluffy, flat-based clouds formed by rising, unstable air. "Cumulus" is
from the Latin for "heap." Cumulus clouds are usually dense and well
defined. They develop vertically in the form of rising mounds; the bulging upper
part often resembles cauliflower. Sunlit parts of these clouds are mostly
brilliant white; their bases are relatively dark and nearly horizontal.
cyclic
Cyclic controls a helicopter's pitch-and-bank attitude (serving the same
function as the yoke or stick that controls the elevator and ailerons in an
airplane). It is the primary airspeed control in flight. Applying forward cyclic
causes airspeed to increase. Aft cyclic reduces airspeed.
cyclone (low)
An area of low atmospheric pressure with a closed, cyclonic circulation. Viewed
from above, the circulation is counterclockwise in the Northern Hemisphere,
clockwise in the Southern Hemisphere, and undefined at the equator. Because
cyclonic circulation and relatively low atmospheric pressure usually coexist, in
common practice, the terms "cyclone" and "low" are used
interchangeably. Also, because cyclones often are accompanied by inclement
(sometimes destructive) weather, they are frequently referred to simply as
storms. "Cyclone"" is frequently misused to denote a tornado.
datum
An imaginary vertical plane or line used as a reference in weight-and-balance
calculations; specifically, the line from which all "arm" measurements
are taken. The center of gravity (CG) is often referenced from the datum. The
aircraft manufacturer sets the datum for a particular airplane. Most
manufacturers set the datum at the position of the firewall separating the
engine from the passenger compartment or at the tip of the propeller spinner.
da Vinci, Leonardo
1452–1519. Italian artist and scientist; a man of towering intellect and a
leader in the transition from the medieval to the modern European consciousness.
Da Vinci's scientific interests included anatomy, botany, geology, optics, and
mechanics. His designs for human-powered flying machines verged on the fanciful,
but his sketches for a hypothetical parachute were scientifically sound.
dead reckoning (de’d reckoning)
The navigation of an airplane solely by computations based on airspeed, course,
heading, wind direction and speed, ground speed, and elapsed time. The term
derives from "deduced" reckoning. Also known as "ded
reckoning."
deadstick
To execute a landing without engine power.
decision height (DH)
The altitude at which, during an ILS or other precision landing approach, a
pilot must decide whether to land or execute a missed approach. A typical ILS
approach has a DH of 200 feet (60 meters) above ground level.
density altitude
Pressure altitude corrected for variations from standard temperature. Density
altitude measures the actual density of the air and, therefore, is a critical
factor in calculating aircraft performance. If the temperature is warmer than
standard, density altitude is higher than pressure altitude, and vice versa. For
example, assume an airport is 3,000 feet (914 meters) above sea level and the
altimeter setting is 29.92 (1013.2 millibars). If the temperature is 90 F (32
C), the density altitude is 5,592 feet (1,704 meters). An airplane taking off
from this airport performs as if it's at nearly 5,600 feet (1,705 meters). The
engine produces less power, the propeller is less efficient, and the wings
create less lift. The airplane uses more runway to reach takeoff speed and
climbs at a lower rate.
design maneuvering speed
See maneuvering speed.
detonation
The sudden, explosive burning of the air/fuel mixture in the cylinders of a
piston engine. Detonation usually occurs when the air/fuel mixture is too
lean—when there is not enough fuel for the current weight of air entering the
cylinder. Detonation imposes excessive loads on the pistons and other engine
components. If not corrected by enriching the mixture, detonation causes engine
damage and may lead to sudden engine failure.
dew
Water condensed onto grass and other objects near the ground when the
temperature of those objects has fallen below the initial dew point of the
surface air but is still above freezing.
dew point
The temperature to which air must be cooled to reach saturation, that is, 100
percent relative humidity. Weather reports usually include the air temperature
and dew point temperature. A narrow "temperature/dew point spread"
(less than 2.8 C or 5 F) indicates a strong likelihood of fog, clouds, or
precipitation.
dihedral
The angle at which an aircraft's wings tilt upward from the fuselage forming a
slight "V" shape as seen from head-on. Dihedral increases stability
about the longitudinal, or roll, axis of an airplane. It tends to level the
wings after an airplane is established in a shallow bank. Anhedral, tilting the
wings downward, produces the same effect, but it is much less common.
directional gyro
See heading indicator.
direct user access terminal (DUAT)
Automated weather service in the United States allowing pilots to receive
weather briefings and file flight plans using personal computers.
dirigibles
A general term for airships or lighter-than-air powered aircraft. An engine and
the ability to steer distinguishes airships from balloons. From the Latin,
dirigere, "to direct."
disk cache
An information storage area. Flight Simulator stores scenery information in a
cache directory on your hard drive for quick access as you fly.
distance-measuring equipment (DME)
Avionics that determine and display distance in nautical miles. DME equipment,
which operates in the UHF band, is usually installed at a VOR station. A
complementary unit installed in the aircraft transmits timed pulses to the
ground station, which replies. The unit in the aircraft converts the time
between the pulses and the replies into distance and also derives ground speed
and time to reach the station. The distance displayed by DME equipment is the
"slant range" from the station, that is, the length of the hypotenuse
of a right triangle formed by the aircraft's altitude and its distance from the
station as measured along the ground. The difference between the slant range and
the aircraft's actual distance from the station is negligible when the aircraft
is more than about 10 nm from the station and at a moderate altitude.
downburst
A strong downdraft that results in damaging winds at or near the ground. The
size of a downburst can vary from less than one-half mile to more than 10 miles.
downdraft
A relative small-scale downward current of air often observed on the lee side of
large objects that restrict the smooth flow of the air, or in precipitation in
or near cumuliform clouds.
downwind
The leg of a standard left or right traffic pattern that is parallel to the
runway but prior to the turn to base and final.
drag
The resistance of an object to movement through a fluid. With respect to
aircraft, drag is one of the four fundamental forces in flight. It opposes
thrust. There are two basic types of drag. Parasite drag is caused by friction.
The airplane surface, antennas, landing gear, and other appendages all cause
parasite drag, which increases in proportion to the square of the aircraft's
velocity. Induced drag is a by-product of lift. At the tip of a wing, air moves
from the high-pressure area below the wing to the low-pressure area above. The
energy used to create these vortices manifests itself as induced drag, which
increases as airspeed drops.
drift
The displacement of an aircraft from its intended course caused by wind.
drizzle
A form of precipitation composed of small water droplets that appear to float
with the air currents while falling in an irregular path. Drizzle differs from
rain, which falls in a comparatively straight path, and fog droplets, which
remain suspended in the air. In weather reports and forecasts, drizzle is
indicated by the abbreviation DZ. On weather charts in the United States,
drizzle is indicated by a comma (,).
dry adiabatic lapse rate
The rate of decrease of temperature with height when unsaturated air is lifted
adiabatically (due to expansion as it is lifted to lower pressure).
dual
In aviation, this term refers to either the number of sets of controls in the
plane, or the fact that a pilot is flying under the supervision of an
instructor.
dissymmetry of lift
A condition in which the main rotor of a helicopter does not produce lift
equally across the entire rotor disk. This occurs only when in forward flight or
hovering in a wind and is most apparent in a retreating blade stall.
Earhart, Amelia
1897–1937. American aviator and the first woman to fly solo nonstop across the
Atlantic. Earhart was also the first woman to cross the United States nonstop
(1932) and the first pilot to fly solo from Hawaii to California (1935). As an
aeronautics adviser at Purdue University and an active proponent of women's
aviation, she decided to attempt the first around-the-world flight made by a
woman. Her second try in 1937 ended when she and navigator Fred Noonan
disappeared over the Pacific.
EFAS (Flight Watch)
Shorthand for En-route Flight Advisory Service, a weather service provided in
the United States by Flight Service Stations. EFAS disseminates weather reports
and forecasts, particularly en route weather, and receives and distributes pilot
reports (PIREPS). Flight Watch is available throughout the United States on
frequency 122.0 from 5,000 to 17,500 feet (1,500 to 5,000 meters) and on a
variety of discrete frequencies for high-altitude traffic.
effective translational lift
When air moves horizontally across a helicopter blade, the rotor produces more
lift at a given power setting. This occurs in forward flight or when hovering in
a light wind. It might take 90 percent of a helicopter's available power to fly
at 20 knots and take only 80 percent to fly at 45 knots.
electronic flight instrument system (EFIS)
Computer-driven cockpit instruments and displays that replace electromechanical
instruments in many modern flight decks. The EFIS can display basic flight
information, such as engine status, moving maps, checklists, and so on.
elevator
A movable control surface located on the horizontal stabilizer of an aircraft's
empennage, or tail. Although its name implies that the elevator makes the
airplane climb or descend, it actually controls only the aircraft's pitch
attitude, that is, the angle of the nose above or below the horizon. The pilot
moves the elevator by applying forward pressure on the control yoke or stick to
decrease pitch attitude and by applying back pressure to increase the pitch
attitude. On some aircraft, the entire horizontal stabilizer moves. This
arrangement is often called a "stabilator" or "flying tail."
elevator trim
See trim.
empennage
The tail assembly of an airplane. The empennage usually includes the fin
(vertical stabilizer), rudder, horizontal stabilizer, and elevator.
Experimental Aircraft Association (EAA)
One of the largest aviation organizations in the world, the EAA was founded in
1953 by Paul Poberezny and several other aviation enthusiasts as a club for
people who build their own airplanes. The first fly-in convention that same year
attracted about 40 people. Today, the EAA numbers more than 150,000 members
around the world and brings more than 800,000 people each year to its Oshkosh
Fly-In, including homebuilders, restorers of classic and antique aircraft, and
warbird enthusiasts.
Extended Range Twin-Engine Operations (ETOPS)
An FAA certification that allows airlines to operate twin-engine aircraft for
extended distances over water.
fast file
A feature of the Flight Service Station telephone system that allows a pilot to
file IFR flight plans by recording them via voice mail. After the pilot hangs
up, a briefer processes the flight plan.
feather
The action of turning the propeller blades until they are parallel to the
aircraft fuselage. After an engine failure, a windmilling propeller can cause
enough drag to seriously degrade aircraft controllability. Feathering reduces
that drag by reducing aerodynamic forces on the prop, allowing it to stop
windmilling. Feathering the prop is accomplished by moving the propeller levers
in the cockpit into the feather position.
Federal Aviation Administration (FAA)
The federal government agency responsible for the regulation and promotion of
aviation in the United States. The FAA regulates and certifies pilots, aircraft,
airports, and airspace. It also manages the air traffic control system and
supervises and inspects airlines, flight schools, flight instructors,
maintenance technicians, and facilities. The FAA was created in 1958 to
supersede the Civil Aeronautics Authority (CAA). It operated under the name
Federal Aviation Agency until 1966, when it became the Federal Aviation
Administration, an organization within the Department of Transportation.
Federal Aviation Regulations (FARs)
In the United States, the parts of the Code of Federal Regulations that pertain
to the certification and regulation of pilots, flight schools and instructors,
maintenance technicians and facilities, aircraft, air navigation, airspace, air
traffic control, and other activities related to aviation and air commerce.
Pilots must be familiar with and adhere to a variety of FARs. The most important
parts of the FARs for day-to-day operations are: Part 1, Definitions and
Abbreviations; Part 61, Certification: Pilots and Flight Instructors; and Part
91, General Operating and Flight Rules. Other parts pertain to commercial and
airline operations, certificated flight schools, transportation of hazardous
materials, certification standards for aircraft, and procedures for reporting
accidents.
final
The leg of a standard traffic pattern that is aligned with the runway prior to
touchdown. The final approach leg can be short for small planes in light air
traffic or extend out a few miles from the threshold for large planes or in
heavy air traffic.
fix
A reference point in space usually defined by a signal from one or more
navigational aids and used by pilots for navigation.
fixed gear
Landing gear that cannot be retracted.
fixed-base operator
At an airport, a person or an organization that sells fuel, sells or rents
aircraft, and possibly provides flight instruction.
flaps
A hinged portion of an airplane's wing, generally on the trailing edge, that can
be lowered during takeoff and landing to increase the wings' lift and drag. When
partially extended, a flap adds lift by increasing the camber, or curvature, of
the wing. Because flaps extend into the oncoming air, they also increase drag,
helping an aircraft descend steeply without building up speed. Modern aircraft
use several types of flaps; the most common designs are plain, split, and
Fowler. Often confused with ailerons, flaps are not the primary control surfaces
of an airplane.
flare
To level off and establish the correct landing attitude just above the runway
prior to landing. A pilot flares by applying back pressure to the control yoke
or stick, which raises the nose of the aircraft. When done properly, the flare
is a smooth, continuous transition from a nose-low, descending flight path to a
nose-high attitude that almost stops the aircraft's descent.
flight level
The altitude measurement used by aircraft flying above 18,000 ft. Flight levels
are expressed in three digits representing the pressure altitude in hundreds of
feet. An aircraft flying at 35,000 feet is at FL350.
flight path
The track over the earth’s surface defined by an airborne aircraft.
flight plan
Specific information about a flight that is filed either orally or in writing
with air traffic control.
flight school
A facility that offers aviation training.
Flight Service Station (FSS)
A government facility that provides a variety of services to pilots. FSS
personnel take weather observations, brief pilots, coordinate flight plans, and
assist aircraft in distress. In the United States, the FSS network includes one
or more stations in each state. Each FSS typically has responsibility for a
large geographic area. FSS specialists communicate with pilots over a network of
remote transmitters and receivers. They also have direct telephone and computer
connections to air traffic control facilities and search-and-rescue
organizations.
fly-by-wire controls
Electronic flight control system in which there are no direct mechanical links
between the controls in the cockpit and the aircraft's control surfaces. A
computer detects movements of the flight controls, interprets them, and sends
signals to move the rudder, ailerons, and elevators. Fly-by-wire systems were
first used in fighter aircraft to make aircraft more maneuverable and ensure
that the pilot could not exceed the design limitations of the aircraft. Today,
large transports, such as the Boeing 777 and several Airbus models, include
fly-by-wire systems.
fractus
Clouds in the form of irregular shreds. They have a torn, clearly ragged
appearance. The term applies only to stratus and cumulus cloud types, such as
cumulus fractus and stratus fractus.
frame rate
The speed at which successive frames of a computer image display on the screen,
similar to the frames of a movie passing through the light source of a movie
projector.
freezing level
A level in the atmosphere at which the temperature is 0 C (32 F).
front
The boundary between two different air masses. More specifically, a surface,
interface, or transition zone of discontinuity between two adjacent air masses
of different densities.
frontal zone
A front or zone with a marked increase of density gradient. The term is used to
describe an area of rapid transition of meteorological elements.
frontogenesis
The initial formation of a front or frontal zone.
frontolysis
The dissipation of a front.
fuel injection system
A set of controls, pumps, nozzles, and other components used in many piston
engines to deliver fuel to the cylinders. The system squirts fuel directly into
the cylinders or just ahead of the intake valve, where it mixes with air.
Because a fuel injection system requires high-pressure pumps, an air/fuel
control unit, fuel distributor, and discharge nozzles for each cylinder, it's
generally more expensive than a carburetor. However, a fuel-injected engine is
more efficient than a carburetor, and fuel injection is used on most large
piston engines.
fully articulated
One of three types of main rotor systems used in modern helicopters. A fully
articulated system utilizes three or more rotor blades that flap independently
to compensate for dissymmetry of lift. Fully articulated rotor systems are more
expensive than semirigid systems, but are less susceptible to low G conditions
and mast bumping. However, they are more affected by ground resonance.
fuselage
The body of an airplane that holds the crew and passengers or cargo. From the
French, fuselé, for "spindle-shaped."
G force
See Gs.
game pad
A device used as a game controller that consists of a handheld body and several
buttons. Unlike a joystick, the game pad uses a D switch, which is operated by
the user’s thumb, for directional control.
general aviation
In the United States, a term applied to all aviation not related to the military
or scheduled airline service. It includes flight training, charter flights,
flying for pleasure, and business-related aviation. The term is also used to
describe a broad class of aircraft not used by the military or scheduled
airlines. General aviation is sometimes abbreviated as GA.
glass cockpit
Refers to the replacement of conventional cockpit gauges with computerized
cathode ray tubes (CRTs) or liquid crystal displays (LCDs). A number of gauges
are combined into the displays, and the pilot can often flip to different
"pages" to view navigation or aircraft system information.
glide ratio
Ratio of horizontal distance traveled per unit of descent. For example, a
sailplane with a 60:1 glide ratio travels 60 meters forward for every 1 meter it
descends. A typical single-engine aircraft has a glide ratio of about 10:1.
glide path
The vertical path defined by an aircraft in a controlled descent.
glider
See sailplane.
glide slope
The electronic approach path projected as part of an instrument landing system
(ILS). Glide slope transmitters, located near the end of a runway, send out
radio signals to form the proper descent path to the runway. The angle of the
glide slope is usually set about 3 degrees to the horizontal.
Global Positioning System (GPS)
A constellation of satellites that sends signals to a ground-based, seaborne, or
airborne receiver. By interpreting three or more signals, the receiver can give
incredibly precise information about the location of the receiver on the face of
the earth, usually within 50 meters or so.
go-around
An air traffic control command for a pilot to abandon his approach to landing.
Greenwich Mean Time
The local time at the Greenwich Observatory, which lies on the prime meridian,
or 0 degrees longitude. This time, now known officially as Coordinated Universal
Time (UTC), is used in air navigation to provide a standard for proposed
departure and arrival times, weather observations and forecasts, and air traffic
control functions. Also known as Zulu time, UTC is expressed in a 24-hour
format; for example, 6 P.M. is 1800 hours.
ground clearance
In aviation, this usually refers to the distance between the tips of an
aircraft’s propeller blades and the ground surface.
ground effect
A decrease in induced drag as an aircraft flies near the surface. The effect is
caused when the ground interferes with the normal flow of air from below the
wing to the low-pressure area above the wing. Ground effect is most apparent
when an aircraft's height is about one-half wingspan or less above the surface.
In practical terms, an aircraft flying in ground effect stalls at lower airspeed
than normal. Pilots can use ground effect to lift off from a soft or short field
with a minimum ground roll, but they must accelerate to normal flying speed
before climbing away from the surface.
ground fog
In the United States, a fog that conceals less than 0.6 percent of the sky and
that is not contiguous with the base of clouds.
ground loop
An aggravated, uncontrolled, tight turn on the ground, usually during rollout
after landing or while taxiing. A ground loop often involves a turn of more than
90 degrees and frequently results in one wing touching the ground. Aircraft with
tailwheels (often called taildraggers) are most susceptible to this loss of
control because the center of gravity in such aircraft lies behind the main
landing gear.
ground school
The portion of pilot training that is conducted in a classroom on the ground.
ground speed
An aircraft's speed relative to the ground; an aircraft's true airspeed
corrected for the effects of a headwind or tailwind. For example, if an aircraft
is flying level at 120 knots with a 15-knot headwind, its ground speed is 105
knots.
Gs
A measurement of the load factor, or apparent gravity, experienced by an
aircraft during flight. One G represents the force of gravity exerted on a body
at rest. When an aircraft climbs, turns, or accelerates, positive G forces act
upon it. When it descends or decelerates, negative G forces act upon it.
gust
A sudden, brief increase in wind. In weather reports and forecasts, gusts are
indicated by "G," followed by the 2- or 3-digit maximum speed, and
units, usually knots (KT). For example, "G25KT" indicates wind gusting
to a maximum of 25 knots.
gyro
Short for gyroscope, an instrument based on a free-spinning wheel mounted within
a ring. Gyros are used in instruments such as the attitude indicator, heading
indicator, and turn coordinator. Because a spinning gyro maintains its
orientation even when an airplane banks, climbs, or dives, it provides a stable
reference to help pilots control an aircraft while flying in clouds or poor
visibility.
gyroplane
A type of rotorcraft that relies on aerodynamic forces to spin the main rotor
during normal flight.
gyroscopic precession
The reaction of a gyro when a force is applied to the spinning wheel. When force
is applied to a gyro, it reacts as if the force had been applied at a point 90
degrees from the point of actual application, in the direction of rotation.
Precession affects propellers, which act like gyros, and gyro instruments. Its
principal effect is on the heading indicator, which tends to drift over time.
hail
Frozen precipitation often associated with thunderstorms. Hail forms when
supercooled water droplets begin to freeze. After a drop has frozen, other drops
latch on and freeze to it. The hailstone grows—sometimes into a huge iceball.
As hailstones fall through warming air, they begin to melt, and precipitation
may reach the ground as either hail or rain. Rain at the surface does not mean
the absence of hail aloft. You should anticipate possible hail with any
thunderstorm, especially beneath the anvil of a large cumulonimbus. In weather
reports and forecasts, hail is denoted by the abbreviation "GR," from
the French, grêle.
heading
The direction in which the aircraft is pointed, usually in reference to magnetic
north. Because wind pushes an airplane in flight, heading does not necessarily
correspond to the aircraft's path over the ground, that is, its track. For
example, if you want to fly due east with respect to the ground and the wind is
blowing from the north, you must turn the aircraft slightly into the wind to
correct for drift.
heading indicator
A gyro instrument that accurately and quickly shows changes in aircraft heading,
sometimes called the "directional gyro," or "DG." Because
the heading indicator is driven by a gyro, it provides smooth, precise
indication of heading or turns. The compass, which is subject to acceleration,
deceleration, dip, and other errors, often oscillates or leads or lags a turn.
However, because gyros are affected by precession, the pilot must periodically
set the heading indicator to correspond to the compass (unless the heading
indicator is "slaved" electronically to the compass).
headwind
A wind that blows in opposition to the intended course of flight.
high
An area of high barometric pressure. Also called an anticyclone or high-pressure
system.
high-performance airplane
As defined in FAR 61.31(e), an airplane that has more than 200 horsepower or
that has retractable landing gear, flaps, and a controllable propeller. A
private or commercial pilot may not act as pilot in command of a
high-performance airplane unless a flight instructor has certified that the
pilot is competent to fly such aircraft.
holding pattern
An ovoid-shaped pattern flown in reference to a fixed (nav radio) reference
point. Holding patterns are assigned by ATC to provide traffic separation during
peak load times.
hood
A view-limiting device worn by pilots who are learning or practicing flight by
instruments. The hood covers the upper portion of the pilot's field of vision. A
safety pilot or instructor must always accompany a pilot who is using a hood.
horizontal situation indicator (HSI)
An instrument that combines the functions of the heading indicator and the VOR
indicator in one display.
horizontal stabilizer
The horizontal surface of the tail, or empennage. The horizontal stabilizer is
an airfoil that creates a downward force on the tail to balance the upward force
generated by the wing. It also incorporates the elevator, the control surface
used to adjust the aircraft's pitch attitude. On some airplanes, the entire
horizontal stabilizer acts as an elevator.
horsepower
A unit of power equal to 745.7 watts or 33,000 foot-pounds per minute. The power
exerted by one horse pulling.
hypersonic
Speeds at or above Mach 5 (that is, five times the speed of sound).
hypoxia
A condition in which an insufficient amount of oxygen reaches the tissues of the
human body. The complete lack of oxygen, called anoxia, is fatal. Hypoxia is a
serious hazard at high altitudes, particularly because its warning symptoms are
varied and sometimes difficult to detect. Cabin pressurization or oxygen
equipment is generally necessary for flying at altitudes at or above 10,000 feet
(3,048 meters).
IFR en route charts
Navigational charts that depict aids to navigation, airways, and restricted
airspace. Used for navigation by pilots flying instrument flights.
Immelmann
An aerobatic maneuver said to have been invented by World War I ace Max
Immelmann in which an airplane reverses its direction of flight while gaining
altitude. The maneuver begins with a half loop. At the top of the loop, the
pilot rolls the plane upright. In modern aerobatic competitions, an Immelmann is
called a "half loop, half roll."
Immelmann, Max
1890–1916. One of Germany's first great fighter pilots, credited (probably
erroneously) as the inventor of the "Immelmann" maneuver. Nicknamed
"the Eagle of Lille," Immelmann learned the basics of air combat from
Oswald Boelcke, with whom he often flew missions. Among the numerous decorations
Immelmann earned before being killed in action was the coveted Blue Max.
inclinometer
An instrument that displays the inclination to the horizontal of an axis. In
most aircraft, there is an inclinometer at the bottom of the turn coordinator.
It indicates when the aircraft is yawing to the left or right.
indefinite ceiling
A ceiling classification that describes vertical visibility into a surface-based
obscuration.
indicated airspeed (IAS)
The speed shown on the airspeed indicator uncorrected for variations in
atmospheric density, installation error, or instrument error. Except at sea
level under standard atmospheric conditions, IAS does not correspond to the
aircraft's actual speed through the surrounding air (that is, its true airspeed,
or TAS).
indicated altitude
Altitude read directly from the altimeter after it is set to the local
barometric pressure corrected to sea level. Indicated altitude is not corrected
for temperature. Pilots use indicated altitude to control their aircraft.
induced drag
The portion of total drag created by lift. Induced drag is created when
high-pressure air below a wing swirls around the wing tip to the low-pressure
area above. This motion creates vortices, which in effect siphon off the
aircraft's energy. This lost energy is induced drag. Induced drag increases as
airspeed decreases.
infrared
Electromagnetic radiation with wavelengths beyond the red end of the visible
color spectrum. Infrared photography, used in aerial surveillance, can penetrate
haze and clouds to capture images of objects that are not visible to the naked
eye.
initial climb
An aircraft’s climb away from the runway after liftoff.
inner marker
Marker beacons are selective signal transmitters used in conjunction with
instrument landing systems. The inner marker is located between the middle
marker and the runway threshold. Used during Category II instrument approaches,
it is the point at which an aircraft will be decision height on the glide slope.
instrument approach chart
Also known as the "approach plate." Approach charts depict, both
horizontally and in elevation, the procedure to be flown during an instrument
approach at a specific airport.
instrument approach procedure (IAP)
An official procedure designed to guide aircraft to a runway when a visual
descent isn't possible. IAPs describe the route and altitude aircraft are to fly
as they transition from en route flight to landing. There are two basic types of
instrument approach procedures: nonprecision and precision. Nonprecision
approaches do not have an electronic glide slope to provide vertical guidance to
landing aircraft. Examples of nonprecision approaches include VOR, NDB,
localizer, and GPS approaches. Precision approaches have electronic glide slopes
that provide precise vertical guidance. The most common precision approach is
the ILS.
instrument flight rules (IFR)
In the United States, regulations that apply to pilots, aircraft, and aircraft
operations when weather conditions do not meet the criteria for visual flight,
when aircraft are operated in Class A airspace—that is, at altitudes at and
above 18,000 feet (5,486 meters), or when pilots choose to operate in controlled
airspace under those rules regardless of the prevailing weather. The rules
establish minimum fuel reserves, equipment requirements and checks, and other
operational standards for instrument flight.
The abbreviation "IFR" is sometimes used to describe weather that doesn't meet the minimums established for flight under visual flight rules (VFR). For example, if an air traffic controller alerts a pilot to nearby traffic and the pilot is flying in the clouds, the pilot may say, "I'm IFR" and ask for a change in heading or altitude to avoid a conflict. The proper abbreviation for describing those conditions is "IMC," for "instrument meteorological conditions."
instrument flight time
Flight time during which the pilot operates an aircraft solely by reference to
instruments under actual or simulated instrument flight conditions. Instrument
flight time is not necessarily the total time during which an aircraft operates
under instrument flight rules (IFR).
instrument landing system (ILS)
A system of navigation aids and approach lights that provide both horizontal and
vertical guidance to aircraft approaching a runway. The ILS is the primary
precision-approach system in use today around the world. A typical ILS includes
a localizer and a glide slope, as well as outer, middle, and inner marker
beacons. The localizer transmits a directional signal that provides left/right
guidance. The glide slope is an electronic glide path that defines the proper
descent angle to the runway. Marker beacons indicate distance from the runway.
instrument meteorological conditions
Weather conditions that require flight under instrument flight rules (IFR). In
controlled airspace in the United States, IMC conditions generally mean that the
ceiling is less than 1,000 feet (305 meters) and flight visibility is less than
3 miles (5 kilometers).
instrument rating
A rating added to a pilot certificate that allows a pilot to act as pilot in
command of an aircraft solely by reference to flight instruments. An instrument
rating is required for operations in clouds or when the ceiling and visibility
are less than required for flight under visual flight rules (VFR). A pilot also
must hold an instrument rating to act as pilot in command of an aircraft in
class A airspace. In the United States, class A airspace begins at 18,000 feet
(5,486 meters) above mean sea level.
instrument scan
A methodical scan of the primary flight instruments during a flight in
instrument flight conditions (flight by reference to the instruments).
instrument
From 14 CFR Part 1: "A device using an internal mechanism to show visually
or aurally the attitude, altitude, or operation of an aircraft or aircraft part.
It includes electronic devices for automatically controlling an aircraft in
flight."
intercooler
A mechanical device between the turbocharger and the carburetor. When the
turbocharger compresses air, the air becomes too hot to use. The air is cooled
by being passed through the intercooler before it enters the induction system.
International Civil Aviation Organization (ICAO)
Based in Montreal, this body sets international standards for airports, pilots,
communications, and other matters related to air transportation.
International Standard Atmosphere (ISA)
An arbitrary standard established as a baseline for calculations used in
meteorology, aviation, and aerodynamics. A set of standard conditions exists for
each altitude. At sea level, standard conditions are defined as 29.92 inches of
mercury (1,013 millibars) and 59 F (15 C).
intersection
In aviation, a point in space defined by the intersection of signals from two or
more navigation transmitters.
interstage turbine temperature (ITT)
Temperature of gases in a turbine engine as measured between the high-pressure
and low-pressure turbine wheels. ITT is a limiting factor of the amount of power
an engine can produce.
inversion
An increase in temperature with height. An inversion is the reverse of the
normal decrease of temperature with height in the troposphere.
inverted
Upside down.
isobar
A line of equal or constant barometric pressure, as shown on a weather chart.
isogonic line
A line on a chart connecting points of equal magnetic variation.
isotherm
A line of equal or constant temperature, as shown on a weather chart.
Jet-airways
Airways delineated by navigation radio signals for high routes (18,000 to 45,000
feet MSL). Sometimes referred to as "J" airways, or highways in the
sky.
jet blast
The high-velocity stream of air exiting a jet engine’s exhaust nozzle.
jet stream
A quasihorizontal stream of winds of 50 knots or more concentrated within a
narrow band. The term usually applies to such winds embedded in the westerlies
in the high troposphere.
Johnson, Clarence "Kelly"
1910–1990. American airplane designer and head of Lockheed's Advanced Project
Development Group for 30 years. Johnson, known as the "King of the Skunk
Works" at Lockheed, made major contributions to the development of more
than 40 airplane models, including the Electra, the Constellation, the U-2
spyplane, and the SR-71 Blackbird.
joystick
Name sometimes given to the stick used to control the ailerons and elevators in
some aircraft. The joystick is said to have been invented by French aviator
Robert Esnault-Pelterie in 1907.
In Flight Simulator, "joystick" refers to an input device connected to
a computer's game port and used to control the ailerons and elevator. A computer
joystick may also incorporate buttons and switches to control the throttle,
landing gear, flaps, and other functions.
katabatic wind
A wind blowing downslope.
kneeboard
A clipboard used in the cockpit to hold charts and other items the pilot needs
to have at hand. Kneeboards are sometimes, but not always, strapped to the
pilot’s knee.
knots
Nautical miles per hour. Abbreviation: kt, kts, or KTS. One nautical mile (nm or
NM) measures 6,076 feet (1,852 meters). This distance is based on the length of
one minute of arc of a great circle—an arc representing the shortest distance
between two points on a globe. One knot equals about 1.15 statute miles per
hour; therefore, 100 knots equals about 115 mph (185 kilometers per hour), 150
knots equals about 172 mph (278 kilometers per hour), and 200 knots equals about
230 mph (370 kilometers per hour). All speeds filed on flight plans and for air
traffic control purposes are in knots. In the United States, light aircraft
manufactured in 1976 and later have airspeed indicators marked in knots. Earlier
models had airspeed indicators marked in statute miles per hour.
Note that "knots" by definition assumes "per hour." You
should never state speed as "knots per hour.
landing gear
The wheels, struts, and other equipment that an aircraft uses to land or
maneuver on the ground. Also known as the "undercarriage." The two
most common types of landing gear are "taildragger" and
""tricycle" arrangements. On a taildragger, the front of the
aircraft is supported on two wheels, while the tail rests on the ground on a
skid or a tailwheel. With tricycle landing gear, the aircraft sits level on the
ground with one nosewheel and two wheels farther back on the aircraft. The main
landing gear are those nearest the airplane's center of gravity. Main landing
gear almost always come in pairs and are designed to withstand a greater landing
shock than the more-fragile nosewheel or tailwheel.
landing roll
The distance from the point where an aircraft touches down on the runway to the
point where the aircraft comes to a stop or can exit the runway.
landplane
An airplane with wheels that can land on land, as opposed to a floatplane or a
skiplane.
lapse rate
The average decrease of temperature with altitude. In the lower level of the
atmosphere, the standard lapse rate is 2 C (3.6 F) per 1,000 feet (305 meters).
Weather forecasters and pilots use the actual lapse rate to estimate the
altitude at which the temperature and dew point will merge and lead to the
formation of clouds or precipitation. An increase in temperature with altitude
is an inversion.
large aircraft
In the United States, an aircraft with a maximum certificated takeoff weight of
more than 12,500 pounds (5,670 kilograms). To act as pilot in command of a large
aircraft, a pilot must have a type rating for that aircraft.
laser
A device that produces an intense, focused beam of energy in the form of light
rays.
lateral axis
One of the three axes of an aircraft, the lateral axis is defined by an
imaginary line running from wing tip to wing tip. Movement about the lateral
axis is called "pitch" and is controlled by the elevator.
leading-edge slats
Openings near the forward edge of a wing designed to allow more air to flow over
the top of a wing at high angles of attack, thus delaying the onset of a stall.
Leading-edge slats and flaps are often known as high-lift devices.
Lear, William Powell
1902–1978. American designer and manufacturer of business jets. Despite the
fact that his education stopped at the eighth grade, Lear built a successful
electronics business. He sold it to finance a new aircraft company, which he
started up in 1962 to build business jets based partly on fighters he had helped
design for Swiss American Aviation Corporation.
left-turning tendency
The result of four forces that together cause a propeller-driven aircraft to yaw
to the left. This tendency is most pronounced when the airplane is flying at a
low airspeed and a high angle of attack. The pilot compensates by applying and
holding right rudder pressure.
The four forces are: the reactive force, the spiraling slipstream, gyroscopic precession, and "P factor." The reactive force is the opposite and equal force generated by the rotation of the propeller. This force induces a rolling motion about the airplane's longitudinal axis. The spiraling slipstream is the rotating column of air produced by the propeller. It swirls around the fuselage and strikes the left side of the vertical stabilizer, producing a left yaw. Gyroscopic precession occurs when the nose of the airplane rises or falls. This change in pitch attitude applies a force to the spinning mass of the propeller, which is 90 degrees ahead of the point where the force was applied. "P factor," or asymmetric propeller loading, induces a left yawing motion because the downward-moving propeller blade has a higher angle of attack and produces more thrust than the upward-moving blade.
lenticular cloud (lenticularis)
A species of cloud whose elements have the form of more or less isolated,
generally smooth lenses, or almonds. These clouds appear most often in
formations of orographic origin—the result of lee waves—in which case, they
remain nearly stationary with respect to the terrain (standing cloud), but they
also occur in regions without marked orography.
lift
The upward force produced by an airfoil, such as a wing interacting with the
air. Lift acts at right angles to the relative wind or the aircraft's flight
path. Lift, one of the four fundamental forces in flight, is opposed by weight.
liftoff
The moment at which an aircraft leaves the ground during takeoff.
light aircraft
Generally speaking, small single- and twin-engine aircraft. More precisely, in
the United States, aircraft with a maximum-certified takeoff weight of 12,500
pounds(5,760 kilograms) or less.
light-gun signals
Colored lights that control tower operators use to issue instructions to
aircraft without radios or to aircraft that have a radio failure. The red,
green, and white lights convey such messages as "cleared to land,"
"stop," and "exercise extreme caution." The meaning of all
the signals is defined in FAR 91.125.
light icing
Ice, regardless of type, that accumulates slowly. Anti-icing or deicing
equipment prevents accumulations. Light icing may become hazardous to aircraft
without anti-icing or deicing equipment if conditions persist for an hour or
more.
light turbulence
In aviation weather reports and pilot reports, turbulence that momentarily
causes slight, erratic changes in altitude, attitude, or both. When light
turbulence produces rhythmic bumpiness without appreciable changes in altitude
or attitude, it is called "chop." In light turbulence, occupants may
feel a slight strain against seat belts or shoulder straps. Unsecured objects
may be displaced slightly. On large aircraft, food service may be conducted and
walking is possible with little or no difficulty.
lightning
Short, intense electrical discharges generated by thunderstorms. Lightning is
rarely a great hazard to most aircraft, but it can damage electronic equipment.
Lightning can also temporarily blind a pilot.
Lilienthal, Otto
1848–1896. German aeronautical engineer and hang glider pilot whose
experiments with stability, lift, and control were highly influential to such
later aviators as the Wright brothers. Lilienthal applied his studies of bird
flight and aerodynamic theory to the design, construction, and experimental
flight of 18 gliders. The first man to be photographed in a glider, Lilienthal
was killed when one of his craft crashed in 1896.
Lindbergh, Charles A.
1902–1974. American aviator who was the first pilot to make a solo, nonstop
flight across the Atlantic, for which he won the Orteig Prize and the Medal of
Honor. Lindbergh started his career as a barnstormer and airmail pilot. After
his historic flight, he and his wife Anne mapped air routes for Pan Am.
Lindbergh eventually moved to Hawaii, where he wrote several books, including
The Spirit of St. Louis, which won a Pulitzer Prize in 1954.
load factor
The ratio between the total load supported by an aircraft's structure and the
actual weight of the aircraft and its contents; also known as "Gs." In
steady-state flight, the load factor is 1. When an aircraft turns or pulls up
out of a dive, load factor increases. For example, an airplane in a level turn
at a bank angle of 60 degrees experiences a load factor of 2. In such a turn,
the aircraft's structure must support twice the airplane's weight and the pilot
must increase the aircraft's pitch attitude to produce more lift.
local airport advisory
Pertinent, known field conditions and local weather provided to pilots by a
Flight Service Station or the military for airports without an operating control
tower.
local weather area
In Flight Simulator, a user-defined region with similar weather characteristics.
You can create two local weather areas, each with a different type of weather.
Unless you specifically create a local weather area, all weather characteristics
are assigned to the global weather area.
localizer
The component of the instrument landing system (ILS) that provides left-right
guidance to a pilot approaching the runway. The localizer is a highly
directional radio signal transmitted on one of 40 channels between
108.10–111.95 MHz. The beam is funnel-shaped. It is typically 10 degrees wide
18 nautical miles from the runway, narrowing to just 700 feet (213 meters) wide
at the threshold.
logbook
An FAA-required record of events to be kept by pilots listing all flight
activity. Also required by the FAA are logs on engines, airframes, propellers,
and rotors showing the amount of time in service and any maintenance performed
on each part.
Lomcevàk
A tumbling aerobatic maneuver. First conceived of by Ladislav Bezàk, a former
world-champion aerobatic pilot, the maneuver has at least five variations—all
initiated from a near-vertical attitude and flown under negative G forces.
Although Lomcovàk is commonly believed to be the Czech or Polish word for
"headache," it apparently comes from a Slovak slang term for a large,
stiff drink.
longitudinal axis
An imaginary line running from the nose to the tail of an aircraft; one of the
three axes of an aircraft. Rotation about the longitudinal axis is called
"roll" and is controlled using the ailerons.
longitudinal separation
A minimum distance expressed in minutes or miles between aircraft at the same
altitude.
loop
An aerobatic maneuver in which an aircraft flies in a complete vertical circle.
An outside loop, begun at the top of the circle, is considerably more difficult
to perform, because the pilot encounters negative G-forces throughout the
maneuver.
low
An area of low barometric pressure, including the attendant system of winds.
Also called a barometric depression, or cyclone.
low G
A condition in which a helicopter's rotor blades have a load of less than 1 G
(the weight of the helicopter) exerted upon them. This can occur due to abrupt
cyclical control movements, flying in turbulence, or when pushing over from a
steep climb. When pushing over from a steep climb, a low G condition will cause
the nose to drop and the aircraft to roll to the right. The main rotor may hit
the tail boom, and helicopters with semirigid rotor systems may experience mast
bumping. Either effect could cause the loss of the main and tail rotors.
Recovering from a low G condition before losing control entails gently appling
aft cyclic to raise the nose and load the main rotor. Apply left cyclic to
counteract the right-turning tendency.
Mach, Ernst
1838–1916. Austrian physicist and member of the Austrian Parliament. Mach's
writings on empirical methodology and his theories on sensation and perception
established the study of the philosophy of sciences. His work in ballistics and
on measuring the speed of sound contributed greatly to the branch of
aerodynamics concerned with supersonic flight.
Mach number
The ratio of an aircraft's speed to the speed of sound. The speed of sound
varies with the density of the medium carrying the sound waves. For example,
sound travels faster through iron or water than through air. Because the density
of air decreases with altitude, the speed of sound also decreases. Sound travels
at approximately 1,226 kilometers per hour (762 mph) at sea level, 1,138
kilometers per hour (707 mph) at 20,000 ft (6096 meters), and 664 mph (1,068
kilometers per hour) at 35,000 feet (10,668 meters). Named for Ernst Mach,
Austrian physicist.
Mach 1
The speed of sound. Mach 1 varies according to altitude and temperature: At sea
level, it is about 762 mph (1,226 kilometers per hour); at the bottom of the
troposphere, Mach 1 is about 660 mph (1,062 kilometers per hour). Above the
tropopause, at about 36,000 feet (11,000 meters), the speed of sound remains
constant.
magnetic compass
A device for determining direction relative to the earth's magnetic field.
magnetic course
A line drawn on a chart between two points with its direction referenced to the
earth's magnetic North Pole.
magnetic declination
See magnetic variation.
magnetic heading
The direction in which an aircraft is pointed, measured relative to the magnetic
north pole. The magnetic heading is displayed on the compass. A pilot determines
the magnetic heading to fly by compensating for the difference between true
north and magnetic north and then adjusting the resulting magnetic course to
compensate for wind. If the wind is blowing directly along the intended course,
the magnetic heading equals the magnetic course. If a crosswind component is
present, however, a pilot must turn the aircraft slightly into the wind to
compensate. Under these conditions, the airplane's track over the ground is
slightly different from the direction in which the nose is pointing.
magnetic variation
The angle between "true north" and "magnetic north"; that
is, the angle between the geographic North Pole and the magnetic North Pole as
measured from a point on the earth. To determine the magnetic course between two
points on the earth's surface, a pilot must determine the true course—the
angle formed between the line drawn on a chart and lines of longitude—and then
add or subtract the variation at points along that course.
magneto
A device that creates an electric current by rotating a magnet. In aircraft
engines, the crankshaft turns the magnetos, which provide the electrical energy
to fire the spark plugs. This arrangement ensures that the spark plugs fire even
if the aircraft's battery and electrical system fail. Certified aircraft engines
typically have two sets of magnetos for additional redundancy.
maneuvering speed (Va)
The maximum speed at which the pilot can use full, abrupt control movement
without creating excessive G forces that could damage the aircraft; the maximum
speed at which you can safely stall an aircraft. Pilots also use maneuvering
speed when flying through turbulent air.
Abbreviated "Va," maneuvering speed is not marked on the airspeed indicator.
manifold pressure gauge
An instrument that measures the air pressure in the intake manifold of a piston
engine. Usually calibrated in inches of mercury, this instrument (really a
barometer) is used in combination with the tachometer to set engine power. Most
small training aircraft have only a tachometer. Aircraft with larger engines and
aircraft with constant-speed propellers usually have manifold pressure gauges.
manually coordinated flight
See uncoordinated flight.
marker beacons
Low-power radio beacons that identify specific positions along an instrument
approach, usually an ILS. A typical ILS has at least two marker beacons. The
outer marker (OM) normally indicates the point at which an aircraft intercepts
the electronic glide slope. It transmits three dashes in Morse code. On the
instrument panel, the OM is indicated by a blue light. The middle marker (MM)
indicates a position about 3,500 feet (1,067 meters) from the runway threshold.
It also marks the point where an aircraft is about 200 feet (61 meters) above
the elevation of the runway touchdown zone. The middle marker transmits a
"dot-dash-dot-dash" code and is indicated in the cockpit by an amber
light.
Some ILSs also have an inner marker (IM), which indicates the point at which an airplane flying along the proper glideslope reaches the decision height. The inner marker transmits a rapid "dot-dot-dot-dot" code and is indicated in the cockpit by a white light.
maximum L/D
Maximum lift-to-drag ratio. This is the speed at which the aircraft will travel
the farthest distance for a given altitude at a given weight. Also known as Best
Glide.
minimum sink
The speed at which the aircraft will lose the least amount of altitude over time
at a given weight.
mayday
The international call for help. The term comes from the French phrase,
m’aidez (help me), pronounced "mayday." This is the
voice-transmission equivalent of the letters SOS used in code transmissions.
mean sea level (MSL)
The average level of the earth's oceans; used as reference for true
altitude—the vertical distance of an aircraft above sea level. Airport,
terrain, and obstacle elevations shown on aeronautical charts are expressed as
true altitude.
measured ceiling
A ceiling classification applied when the ceiling value has been determined by
instruments or the known heights of unobscured portions of objects other than
natural landmarks.
medical certificate
In the United States, a certificate showing that a pilot, required flight
crewmember, or air traffic controller meets a set of physical and mental
standards established for the safe operation of an aircraft or the performance
of other duties. The FAA issues third-, second-, and first-class medical
certificates. The certification standards are more restrictive with each class.
Student, recreational, and private pilots are required to hold at least a
third-class medical certificate, which is valid for either 24 or 36 months. A
second-class medical is required for certain commercial operations. It is valid
for 12 months for those operations and for 24 months for noncommercial
operations. Airline pilots require a first-class medical, which is valid for 6
months for air carrier operations, 24 months for certain commercial operations,
and 24 months for noncommercial operations.
METAR
From the French term for Aviation Routine Weather Report, the worldwide standard
report for hourly weather observations taken at airports. The United States
recently adopted the METAR to replace SA reports. A METAR includes the following
information: type of report, station designator, time of report, wind,
visibility, weather and obstructions to visibility, sky condition, temperature
and dew point, altimeter setting, and any remarks.
microburst
Violent, localized winds often associated with thunderstorms. In a microburst,
strong vertical downdrafts spill out of a thunderstorm and then spread along the
ground, like water poured from a bucket. These downdrafts can exceed 6,000 feet
per minute (1,829 meters per second) and create strong wind shears—areas where
the speed and direction of the wind change abruptly. An airplane flying through
a microburst and the associated wind shear experiences rapid changes in airspeed
and can even sink to the ground if caught in a strong downdraft.
middle marker
A marker beacon located approximately 3,500 feet from the runway threshold. This
is the point at which an aircraft will be approximately 200 feet AGL on the
glide slope.
millibar (mb)
An international unit of pressure equal to 1,000 dynes per square centimeter. It
is convenient for reporting atmospheric pressure.
mixed ice
A combination of clear and rime ice that can form rapidly. Mixed ice forms when
water drops vary in size or when liquid drops are intermingled with snow or ice
particles. Ice particles become imbedded in clear ice, building a rough
accumulation, sometimes in a mushroom shape, on the leading edges of an
aircraft's surfaces.
mixture control
A device for controlling the ratio between fuel and air entering an engine's
carburetor or fuel injection system. In most aircraft, the mixture control is a
push-pull knob or lever marked in red, usually located to the right of the
throttle.
Because aircraft engines operate over a wide range of altitudes, the pilot must adjust the mixture to produce the most efficient fuel/air mixture as an airplane climbs into less dense air or descends into more dense air. A mixture that is too rich contains too much fuel for the existing conditions and causes the engine to run rough and lose power. A mixture that is too lean can cause an engine to overheat or can cause detonation—the sudden, explosive combustion of fuel within the cylinders.
mmo
Abbreviation for Mach maximum operating speed; the maximum airspeed, indicated
in Mach number, at which an aircraft can be operated safely. The actual value of
mmo varies with atmospheric pressure, temperature, and other factors.
moderate icing
Ice, regardless of type, that accumulates at a rate that requires the use of
anti-icing or deicing equipment. Aircraft without such equipment must divert
immediately.
moderate turbulence
In aviation weather reports and pilot reports, turbulence that causes changes in
altitude or attitude and small variations in airspeed. The aircraft remains in
positive control at all times, Occupants feel definite strains against seat
belts or shoulder straps. Unsecured objects are dislodged. On large aircraft,
food service and walking are difficult.
monoplane
An airplane having only one main pair of wings. Monoplanes create less drag than
biplanes, but early aircraft relied on biplane designs because of the ease of
constructing a sufficiently strong plane this way. Once engineering advanced to
the stage where strong monoplanes were possible, the biplane design became
obsolete.
Mooney, Al
1906–1986. American airplane designer and manufacturer. Mooney began designing
light airplanes in 1922. He worked for a number of aircraft companies around the
United States, including Bellanca and Culver Aircraft, before joining Dart
Manufacturing to design the Dart monoplane. Mooney designed his M-18 Mite in
1946; that same year, he and his brother Art founded Mooney Aircraft.
mountain waves
A standing wave or lee wave to the lee of a mountain barrier; waves created by
massive amounts of air pushed over mountain ranges, such as the Rockies and the
Sierra Nevada in the United States. Intense mountain waves are typically
produced when a strong, turbulent jet stream flows directly across a mountain
ridge. Sailplane pilots often use mountain waves to soar to high
altitudes—50,000 feet (15,240 meters) or more.
N1
The rotational speed of the low-pressure compressor in a dual-spool gas turbine
engine.
N2
The rotational speed of the high-pressure compressor in a dual-spool gas turbine
engine.
National Aeronautics and Space Administration (NASA)
A civilian agency of the United States government created in 1958 with the
responsibility for all nonmilitary developments in aeronautics and space flight.
NASA replaced the National Advisory Committee for Aeronautics.
National Flight Data Center
A facility in Washington, D.C. established by the FAA for the dissemination of
aeronautical information essential to flight safety.
National Transportation Safety Board (NTSB)
In the United States, the government agency that investigates aircraft accidents
and determines their probable cause. The NTSB is independent of the FAA, which
regulates aviation. The FAA participates in accident investigations and responds
to recommendations made by the NTSB when the board determines that new
regulations, procedures, or equipment would help prevent future accidents.
nautical mile (nm)
A distance of about 6,076 feet (1852 meters). The nautical mile is based on the
length of one minute of arc of a great circle. In aviation, distances and speeds
are measured in nautical miles (nm) and nautical miles per hour (knots).
NAV
Abbreviation for navigational; usually refers to a navigational radio, as in
"NAV 1" or "NAV 2."
NAV/COM
A radio that combines the functions of communication and navigational radios.
navigation lights
The basic anticollision light system required on all aircraft certified to fly
at night. The system includes a red light on the left wing tip, a green light on
the right wing tip, and a white light on the tail. These lights tell other
aircraft which direction an aircraft is flying when only the lights can be seen.
Navigation lights must be turned on between sunset and sunrise.
navigational aid
Any visual or electronic device, either airborne or ground-based, established to
provide point-to-point guidance information or position data to aircraft in
flight.
nimbostratus
A principal cloud type, gray colored, often dark. Its diffuse appearance is
caused by more or less continuously falling rain or snow, which in most cases
reaches the ground. A nimbostratus cloud is thick enough throughout to blot out
the sun.
Ninety-Nines (99s)
Association of women fliers formed in 1929 with 99 charter members, including
Amelia Earhart, Jackie Cochran, Louise Thaden, and Amy Johnson. The Ninety-Nines
were responsible for the acceptance and respect accorded women contestants in
the air races of the 1930s. Today, the Ninety-Nines is a worldwide organization
with thousands of members.
nondirectional radio beacon (NDB)
A radio beacon that transmits nondirectional signals in the low- or
medium-frequency band (190–535 kHz); today, used primarily for NDB
nonprecision approaches and in conjunction with the outer marker component of an
ILS. An automatic direction finder (ADF) points to these beacons.
nonprecision approach
Nonprecision approaches do not have an electronic glide slope to provide
vertical guidance to landing aircraft. Examples of nonprecision approaches
include VOR, NDB, localizer, and GPS approaches.
nose gear
In an aircraft equipped with tricycle landing gear, the wheel located under the
forward end of the fuselage.
nose over
To rapidly lower the nose relative to the horizon; to decrease pitch. On the
ground, a nose over—an aircraft tipping forward or doing a somersault—can
result when the nosewheel digs into a soft surface or when a tailwheel-equipped
airplane decelerates too rapidly.
Notice to Airmen (NOTAM)
A notice containing information not known far enough in advance to publish,
provided for persons concerned with flight operations. NOTAMs generally deal
with changes in facilities, services, procedures, or hazards in the National
Airspace System.
obscuration
In weather reports, denotes a sky hidden by surface-based phenomena and
restricted vertical visibility overhead.
occluded front (occlusion)
A composite of two fronts as a cold front overtakes a warm front, or a
quasistationary front.
oleo-pneumatic
A hydraulic-air system usually incorporated into aircraft landing-gear systems.
Oleo-pneumatic shock absorbers dissipate the shock of landing by forcing fluid
through a restrictor valve from the upper chamber of the strut to the lower
chamber.
omnibearing indicator (OBI)
The instrument that displays information about an aircraft's position relative
to a VOR station. The OBI includes a needle, or course deviation indicator
(CDI), to show the aircraft's position relative to a selected course or
"radial" and a TO-FROM-OFF indicator that shows the aircraft's
position relative to the VOR station. A glideslope needle is also included in
some OBI. Each OBI is typically connected to a navigation receiver (NAV 1 or NAV
2).
ornithopter
Hypothetical human-powered flying machine based on flapping wings. Leonardo da
Vinci was perhaps the first to attempt a scientific design of ornithopters, but
the idea reaches back at least to the Greek legend of Daedalus and Icarus. No
actual ornithopter has ever been built.
orographic
Of, pertaining to, or caused by mountains, as in orographic clouds, orographic
lift, or orographic precipitation.
outer marker
A marker beacon that usually indicates a point at which an aircraft at the
appropriate altitude on a localizer course will intercept the glideslope on an
ILS approach.
oversquare operation
Running with the manifold pressure at a higher setting than the rpm. For
instance, "square" would be 24 inches of manifold pressure (MP) and
2400 rpm. "Oversquare" would be 26 inches MP and 2400 rpm. Pilots used
to be warned not to run the engines oversquare, but now, oversquare is
considered acceptable and can be more efficient.
ozone
An unstable form of oxygen. The heaviest concentrations of ozone are in the
stratosphere. Ozone is corrosive to some metals and it absorbs most ultraviolet
solar radiation.
panel
Equivalent to an automobile’s dashboard, the panel is the surface in which the
aircraft’s instruments and radios are installed. Larger aircraft often have
multiple panels, sometimes on the sides or ceiling of the cockpit.
Pan-Pan
Indicates uncertainty or alert when transmitted three times successively
followed by the nature of the urgency.
parasite drag
Resistance to motion through the air composed of form drag (due to landing gear,
radio antennas, shape of the wings, and so on), skin friction, and airflow
interference between aircraft components (such as the junction of the wings and
fuselage, or fuselage and tail). Parasite drag increases as the square of
velocity. It is one component of total drag, the force that opposes thrust. The
other component is induced drag, a by-product of lift.
partial obscuration
A designation of sky cover when part of the sky is hidden by surface-based
obscuring phenomena.
performance booster
Software to enhance performance of Flight Simulator or scenery add-ons. The
performance booster monitors your aircraft's position and automatically loads
scenery from the CD-ROM drive to a disk cache on your hard drive.
phonetic alphabet
A spoken alphabet endorsed by the International Civil Aviation Organization
(ICAO) and used by pilots and air traffic controllers to avoid confusion during
radio communications. Instead of saying "a," "b,"
"c," pilots say "alpha," "bravo," "charlie,"
and so on.
Pilcher, Percy
1866–1899. Scottish marine engineer whose experiments with gliders between
1895 and 1899 produced a number of design advances. Pilcher was developing a
light engine for use with one of his gliders but did not complete the project.
Like his mentor, Otto Lilienthal, Pilcher died when one of his gliders crashed.
pilot certificate
In the United States, a pilot license. The FAA issues several types of pilot
certificates, including student, recreational, private, commercial, certified
flight instructor, and airline transport pilot certificates. Pilot certificates
define broad privileges and limitations. Ratings on those certificates
(single-engine land, instrument, multiengine land, helicopter, and so on)
further specify the classes of aircraft that a pilot may fly and whether the
pilot is allowed to act as pilot in command when the weather does not meet the
minimums specified for flight under visual flight rules (VFR).
pilot in command
The pilot responsible for the operation and safety of an aircraft during flight
time. For purposes of logging flight time, a pilot holding a recreational,
private, or commercial pilot certificate may log as pilot-in-command time (PIC
time) only that flight time during which that pilot is the sole manipulator of
the controls. The pilot must hold an appropriate pilot certificate and rating
for the aircraft. An airline transport pilot may log as PIC time all of the
flight time during which that pilot acts as PIC. A certified flight instructor
may log as PIC time all flight during which that pilot acts as PIC.
pilot report (PIREP)
A PIREP describes actual in-flight conditions, such as the height of clouds,
visibility, precipitation, turbulence, and icing. On weather reports in the
United States, pilot reports are preceded by the letters "UA." A pilot
report includes the following items: position relative to a weather reporting
station or navigation aid, time (UTC), altitude, aircraft type, cloud types and
altitudes, visibility, outside air temperature, wind, turbulence, and any
remarks. Some of the information may be omitted.
pilotage
Flying cross-country from one visible landmark to another using only a chart.
Piper, Bill
1881–1970. American aircraft manufacturer who founded Piper Aircraft
Corporation in 1937. Piper left his earlier career in oil exploration to invest
in Taylor Brothers, builder of the E-2 Cub. He took over the company in 1932 and
changed its name five years later. Piper Aircraft was, for many years, the
world's leading producer of light aircraft.
piston engine
One of the common terms for an internal-combustion reciprocating engine.
pitch
Movement of an aircraft about its lateral axis (nose up or nose down), or the
angle of an airplane's nose above or below the horizon. The pilot moves the
control stick or yoke forward and back to move the elevator, located on the
horizontal stabilizer. Forward pressure lowers the nose; back pressure raises
the nose.
pitch/power rule
The pitch/power rule states that for normal flight, unless the throttle is fully
open or fully closed, power changes should be used to change airspeed, and pitch
changes should be used to change altitude.
pitot tube
A small metal probe, usually attached to a wing or the nose of an aircraft, that
measures ram air pressure as the aircraft moves. The pitot tube is part of the
pitot-static system. It is connected directly to the airspeed indicator, which
displays the ram air pressure on a scale, usually calibrated in knots. The pitot
tube usually has a heater to prevent ice from blocking the device. The probe is
named after Henri Pitot (1695–1771), a French scientist who invented devices
to measure the flow of water in rivers and canals.
pitot-static system
The sensors, connecting lines, and flight instruments that measure, transmit,
and display information about an aircraft's airspeed, altitude, and rate of
climb or descent. The pitot-static system includes the pitot tube, static ports,
and tubing that connects the sensors and instruments in the cockpit. The
airspeed indicator is connected to both the pitot tube and the static ports. The
altimeter and vertical speed indicator are connected only to the static ports.
pivot point
The center of gravity on an aircraft.
Poberezny, Paul
American fighter pilot and flight instructor in World War II and the Korean War,
and founder and chairman of the Experimental Aircraft Association (EAA).
Poberezny organized the EAA and its first fly-in in 1953, from which he became a
leading figure in representing the interests of sport-flying enthusiasts and
amateur aircraft builders worldwide. Involved in aviation for most of his life,
Poberezny has designed more than 15 airplanes and has served as editor for a
number of aviation publications. His son, Tom, is the current president of the
EAA.
positive control
From 14 CFR Part 1: "Control of all air traffic, within designated
airspace, by air traffic control."
power glide
A long, shallow approach in which engine power is used to maintain the glide.
Power glides should be avoided when they are not required to maintain instrument
flight rule (IFR) approach angles, because an engine failure can cause an
aircraft to land short of the runway.
power plant
An aircraft engine, propeller, and all components necessary for their proper
functioning.
practical test
In the United States, an oral and flight test required for a pilot certificate
or rating. Practical tests are given by government inspectors or designated
examiners. The required knowledge and performance standards for each pilot
certificate or rating are specified in a series of Practical Test Standards
(PTS) available from the Government Printing Office or from many publishers of
aviation-related books and study guides.
precipitation
Any or all forms of water particles, whether liquid or solid, that fall from the
atmosphere and reach the surface. Precipitation is distinguished from cloud and
virga in that it must reach the surface.
precipitation-induced fog
Fog formed when relatively warm rain or drizzle falls through cool air.
Evaporation from the precipitation saturates the cool air and forms fog.
Precipitation-induced fog can become quite dense and persistent. It often
extends over large areas, completely suspending flight operations. It is most
commonly associated with warm fronts, but it can occur with slow-moving cold
fronts and with stationary fronts. Precipitation-induced fog is especially
critical because it occurs in precipitation and related hazards such as icing,
turbulence, and thunderstorms.
preflight briefing
The acquisition of weather conditions and forecasts for a route of flight prior
to takeoff.
pressure altimeter
An aneroid barometer with a scale graduated in altitude instead of pressure.
Using standard atmospheric pressure-height relationships, a pressure altimeter
shows indicated altitude (not necessarily true altitude). It may be set to
measure indicated altitude from any arbitrarily chosen level.
pressure altitude
The altitude indicated when the altimeter is set to 29.92 inches of mercury or
1013.2 millibars. Pressure altitude is used in several important calculations,
including the determination of density altitude, true altitude, and true
airspeed. In the United States, aircraft operating at 18,000 feet (5,486 meters)
or higher fly at "flight levels," which are pressure altitudes. When
operating at or above FL180, the pilot should set the altimeter to 29.92 to
display pressure altitude.
prevailing easterlies
The broad current or pattern of persistent easterly winds in the tropics and
polar regions.
prevailing visibility
In the United States, the greatest horizontal visibility that is equaled or
exceeded throughout half of the horizon circle; it need not be a continuous
half.
prevailing westerlies
The dominant west-to-east motion of the atmosphere, centered over middle
latitudes of both hemispheres.
primary flight instruments
The six instruments displayed on the standard instrument cluster: airspeed
indicator, attitude indicator, altimeter, turn coordinator, heading indicator,
and vertical speed indicator.
private pilot certificate
In the United States, a pilot certificate issued to a person who does not intend
to act as a pilot in command for compensation or hire. To be eligible for a
private pilot certificate, a person must be at least 17 years old and hold a
current third-class medical certificate. To earn a private pilot certificate, a
person must acquire at least 40 hours of flight time, including 20 hours of
flight instruction and 20 hours of solo flight time. The training must include
basic maneuvers, cross-country navigation, and other specific tasks.
procedure turn
A predefined turn during an instrument approach that reverses the aircraft’s
course and puts it on the final approach heading to the runway.
prognostic chart
A chart of expected or forecast weather conditions.
propeller
Often called a "prop;" a rotating airfoil that is driven by an
aircraft engine. The propeller produces thrust when turning and either pushes or
pulls the aircraft through the air.
propwash
The air blown back from an airplane propeller (or rotor, in the case of
helicopters).
pushback
The act of being pushed back from an airport terminal gate. This is usually done
by hooking a small tug to the nose wheel of a large aircraft and pushing it
backwards into the taxi lane. In Flight Simulator, press SHIFT+P to push back
from the gate.
radar
A device for detecting distant objects by reflecting radio waves from their
surfaces. The British first integrated radar into their military defenses, and
its value during the Battle of Britain was enormous. Today, radar is the primary
tool for air traffic control. Some aircraft also carry weather radar, designed
to detect precipitation and wind shears associated with thunderstorms and other
hazards.
radar altitude
The altitude of an aircraft determined by radar or radio altimeter. It is the
actual distance between an aircraft and the ground or water surface directly
beneath it.
radarsonde observation
An observation in which winds are determined by tracking a balloon-borne target
with radar.
radial
One of the 360 "spokes," one for each degree in a circle, radiated
from a VOR station. To fly a specific course, the pilot tunes the appropriate
VOR station and selects a radial to fly. An indicator in the cockpit, called an
OBI, shows the aircraft's position relative to that radial.
radial engine
A type of reciprocating piston engine in which the cylinders are arranged like
the spokes of a wheel.
radiation fog
Fog characteristically formed over land at night or near daybreak when cooling
of the earth's surface lowers the air temperature near the ground to or below
the initial dew point. Radiation fog is especially common on calm, clear nights.
It is relatively shallow and may be dense enough to hide the entire sky.
radio stack
The area where the COM, NAV, and transponder radios are installed in an aircraft
instrument panel. Radios are usually arranged in a vertical column, or stack.
radiosonde
A balloon-borne instrument for measuring pressure, temperature, and humidity
aloft.
rate of climb
The speed (usually measured in feet per minute) at which an aircraft is
climbing. The term sometimes is stretched to include the rate of descent. The
rate of climb is read on the vertical speed indicator (VSI).
rate of climb indicator
See vertical speed indicator (VSI).
rating
In the United States, an endorsement added to a pilot certificate that specifies
the classes of aircraft (single-engine land, instrument, multiengine land,
helicopter, and so forth) that a pilot may fly and whether the pilot is allowed
to act as pilot in command when the weather does not meet the minimums specified
for flight under visual flight rules (VFR).
rate of sink
See sink rate.
rawinsonde observation
A combined winds-aloft and radiosonde observation. Winds are determined by
tracking the radiosonde by radio direction finder or radar.
recreational pilot certificate
In the United States, a pilot certificate issued to a person who intends to fly
only for recreation in basic aircraft. To be eligible for a recreational pilot
certificate, a person must be at least 17 years old and hold a current
third-class medical certificate. To earn a recreational pilot certificate, a
person must acquire at least 30 hours of flight time, including 15 hours of
flight instruction. Recreational pilots are subject to many restrictions. For
example, they may not carry more than one passenger and must remain within 50
nautical miles of an airport where they received flight instruction.
Recreational pilots are restricted to basic single-engine aircraft with no more
than 180 horsepower, four seats, and fixed landing gear. They also cannot fly at
night, above 10,000 feet (3000 meters), or when the visibility is less than 3
sm.
relative humidity
The ratio, usually expressed in percent, between the amount of water present in
the air and the maximum amount that could be present at a given temperature.
Warm air can hold more water vapor than cool air. If temperature increases and
the amount of water vapor in the air remains constant, relative humidity
decreases. If temperature drops while the amount of water vapor stays constant,
relative humidity increases. Air with 100 percent relative humidity is said to
be "saturated." The temperature at which the air reaches 100 percent
relative humidity is called the "dew point."
relative wind
The speed and direction of air striking an airfoil; that is, the air flow caused
by an aircraft or airfoil's movement through the air. The relative wind blows
parallel and opposite to the aircraft's flight path. The angle between the
relative wind and the chord line is the angle of attack. Lift acts perpendicular
to the relative wind.
resolution
The level of graphics detail displayed on a computer screen.
retractable gear
Landing gear that can be retracted into the fuselage of an aircraft. Though they
are more complex than fixed-gear, the ability to retract the gear provides a
significant reduction in drag.
retreating blade stall
A condition in which a helicopter's rotor blades on the left side of the rotor
disk (as viewed from above) exceed their critical angle of attack and stall.
This is most apparent during high forward speed and is the primary limiting
factor on a helicopter's maximum speed. Recovery from a retreating blade stall
entails lowering the collective to reduce the rotor blade's angle of attack and
slowing down.
reverse thrust
An engine's thrust directed forward to help slow the aircraft's forward motion.
On turbojet aircraft, this is accomplished by the use of moveable devices that
are extended across the engine's exhaust path or by movement of the cowling on
high-bypass turbofans. On turboprop engines, this is accomplished by movement of
the propeller blades into a position that directs thrust forward.
ridge
In meteorology, an elongated area of relatively high atmospheric pressure;
usually associated with and most clearly identified as an area of maximum
anticyclonic curvature of the wind flow. In soaring, rising terrain that is
often accompanied by rising air.
ridge lift
An area of rising air created when wind blows against the side of a ridge and is
deflected upward. In such conditions, sailplanes can stay aloft for hours by
flying parallel to a ridge and riding those rising currents of air.
rigid
One of three main types of main rotor systems used in modern helicopters. A
rigid rotor system utilizes three or more rotor blades that flap independently
to compensate for dissymmetry of lift. Unlike the fully articulated system, the
rigid system is hingeless, and the rotors can lead and lag independently.
Rigid rotor systems are typically made of composite materials and titanium (and
are, therefore, expensive) and tend to give a rough ride. They resist low G
conditions and ground resonance, and are less expensive to maintain than other
rotor systems.
rime ice
White or milky and opaque granular deposits of ice formed by the rapid freezing
of supercooled water droplets on exposed parts of an aircraft. Rime ice forms
when drops are small, usually in stratiform clouds or light drizzle. The liquid
portion remaining after initial impact freezes before the drop spreads over the
aircraft surface. The small frozen droplets trap air between them, giving the
ice a milky appearance. Rime ice is lighter than clear ice, but its irregular
shape and rough surface quickly degrade the efficiency of airfoils.
roger
Used to acknowledge that the speaker has understood a radio transmission he or
she has received.
roll
Rotation about an aircraft's longitudinal axis. The pilot controls roll, or the
bank of the wings, with the ailerons. A roll is also an aerobatic maneuver in
which an airplane rotates completely around its longitudinal axis.
roll cloud
A dense and horizontal roll-shaped accessory cloud located on the lower leading
edge of a cumulonimbus. Roll clouds can also be found near a rapidly developing
cumulus cloud. They indicate turbulence.
rotary engine
Type of piston engine, common in World War I aircraft, with a stationary
crankshaft and cylinders that rotate around the crankshaft. Rotary engines were
lighter-weight, more reliable, and more easily cooled than many contemporary
radial and inline piston engines, but they had high fuel consumption and their
rotational inertia sometimes made an aircraft difficult to maneuver.
rotation
Pulling back on the control yoke or stick to raise the nose of an aircraft
during the takeoff roll.
rotation speed (Vr)
The speed at which the pilot should pull back on the control yoke or stick to
begin raising an aircraft's nose during takeoff.
rotor
The rotating airfoil that provides lift or antitorque capabilities on a
helicopter. Can also refer to the moving part of an axial-flow compressor in a
turbine engine.
rotor cloud
A turbulent cloud formation found in the lee of some large mountain barriers,
the air in the cloud rotates around an axis parallel to the range; indicative of
possible violent turbulence.
roundout
See flare.
rudder
A movable control surface usually mounted on the vertical stabilizer of the
tail. The rudder moves the aircraft about its vertical, or yaw, axis. It does
not, however, turn the airplane. It is used primarily to balance forces in turns
and to counteract yawing motions induced by the propeller during flight. A pilot
moves the rudder by applying pressure to the left or right rudder pedal. The
pedals are mounted on the floor of the cockpit. In normal maneuvering, the pilot
uses simultaneous aileron and rudder pressures to maintain balanced or
coordinated flight.
runway
A prepared surface designed for departing or landing aircraft.
run-up
Before taking the runway for takeoff, most pilots of piston-powered aircraft
"run up" the engine(s) to a high rpm setting to test the magnetos and
carburetor heat, and to check vacuum system suction, among other things. Better
to find problems on the ground before takeoff, than in the air.
runway visual range (RVR)
The horizontal distance (in feet or meters) that a pilot should be able to see
down the runway from the approach end. RVR is based on either the sighting of
high intensity runway lights or on the visual contrast of other objects,
whichever yields the greatest visual range.
S turn
A taxiing technique employed by pilots of tailwheel aircraft. Due to the
attitude of a taildragger when it’s sitting on the ground, the nose of the
aircraft limits forward visibility. By alternately turning the aircraft left and
right, the pilot can see ahead of the aircraft.
Also refers to a technique used in flight during training. Student pilots are taught to S turn across a fixed ground reference (such as a road), in order to gain proficiency in making uniform turns.
sailplane
A highly efficient unpowered aircraft that can maintain or gain altitude by
riding thermals or other rising air.
Santos-Dumont, Alberto
1873–1932. Brazilian-born inventor of dirigibles and airplanes who made the
first powered flight in Europe. Santos-Dumont made his first balloon flight
early in 1898; later that year, he became the first to fly a balloon equipped
with an engine. In 1906, he flew his boxlike "14-bis" flying machine
722 feet (220 meters) for the first powered flight outside the United States.
Santos-Dumont retired from aviation in 1910. In 1932, depressed over the
military use of aircraft, he took his own life.
saturated adiabatic lapse rate
The rate of decrease of temperature with height as saturated air is lifted with
no gain or loss of heat from outside sources. This value varies with
temperature, and is greatest at low temperatures.
scan
Refers to the methodical examination of flight instruments during IFR flight.
Can also refer to a methodical examination of the sky around an aircraft when
looking for traffic.
scud
Small detached masses of stratus fractus clouds below a layer of higher clouds,
usually nimbostratus. More generally, "scud" is any low-level clouds
or fog. Pilots who fly at low altitude beneath clouds are said to be "scud
running."
sea fog
A type of advection fog formed when air that has been lying over a warm surface
is transported over a colder water surface.
see and avoid
The responsibility of pilots flying in visual meteorological conditions (VMC) to
look for other aircraft and avoid them.
semimonocoque
A kind of fuselage construction that distributes the structural load of the
aircraft between its skin and the framework.
semirigid
One of three main types of main rotor systems used in modern helicopters. A
semirigid rotor system utilizes two rotor blades that flap together as a unit to
compensate for dissymmetry of lift. Semirigid rotor systems are relatively
inexpensive to maintain but are susceptible to low G conditions, and their
flapping characteristics can lead to mast bumping.
settling with power
Also called a retreating blade stall. A condition in which a helicopter's rotor
blades on the left side of the rotor disk (as viewed from above) exceed their
critical angle of attack and stall. This is most apparent during high forward
speed and is the primary limiting factor on a helicopter's maximum speed.
Recovery from a retreating blade stall entails lowering the collective to reduce
the rotor blade's angle of attack and slowing down.
severe icing
Icing, regardless of type, that accumulates so rapidly that even aircraft
equipped with anti-icing or deicing equipment must divert immediately.
severe turbulence
In aviation weather reports and pilot reports, turbulence that causes large,
abrupt changes in altitude, attitude, or both. Severe turbulence usually causes
wide variations in indicated airspeed. The aircraft may be momentarily out of
control. Occupants are forced violently against seat belts or shoulder straps.
Unsecured objects are tossed about. On large aircraft, food service and walking
are impossible.
shaft horsepower (SHP)
A power output measurement for turboprop engines. SHP is determined by propeller
rpm, and the torque power output of exhaust and shaft forces is called
Equivalent Shaft Horsepower (ESHP).
shock wave
Created when airflow changes abruptly from subsonic to supersonic speed, causing
an enormous increase in air pressure and temperature. When an aircraft travels
above Mach 1, shock waves bend backward to form a cone. If this cone reaches the
earth's surface, it causes an explosive sound called a sonic boom.
shower
Precipitation from a cumuliform cloud. A shower is characterized by the
suddenness with which it begins and ends, by a rapid change of intensity, and
usually by rapid change in the appearance of the sky. Showery precipitation may
be in the form of rain, ice pellets, or snow.
SIGMET advisory (significant meteorological information)
An advisory of concern to all aircraft that covers severe weather conditions.
Sikorsky, Igor
1889–1972. Russian-born aircraft designer and manufacturer considered to be
"the father of the helicopter." Sikorsky built his first helicopter at
age 20, and in 1913, he built the world's first four-engine airplane. After
moving to the United States in 1919, he formed an aircraft company with other
Russian émigrés. Sikorsky's flying boats, although a technical success, were a
financial failure, so with support from United Air Transport, he returned to
helicopters. In 1939, his VS-300 became the first practical helicopter.
sink rate
Negative vertical velocity, usually expressed in feet per second.
simplified directional facility
A navigational aid used for nonprecision approaches. Similar to an ILS, but not
as accurate.
skid
A turn in which the rate of turn is too great for the angle of the bank. In a
skid, the ball at the bottom of the turn coordinator moves to the outside of the
turn. To correct a skid, use the ailerons to increase the bank, reduce rudder
pressure, or both, in the direction of the turn.
slat
A movable auxiliary airfoil on the leading edge of a wing. The slat extends into
the flow of air and creates a gap that allows air to flow smoothly over the top
of the wing, delaying the stall at high angles of attack.
slewing
In Flight Simulator, a method of rapidly changing aircraft position, direction,
location, or altitude without flying.
slip
A turn in which the rate of turn is too slow for the angle of the bank. In a
slip, the ball at the bottom of the turn coordinator moves to the inside of the
turn. To correct for a slip, use the ailerons to decrease the bank, increase
rudder pressure, or both, in the direction of the turn. Pilots also use forward
slips and side slips to correct for crosswinds during landings and to increase
an aircraft's rate of descent without increasing its airspeed.
slow flight
Flight at an aircraft’s minimum controllable airspeed.
solo
Flight during which only one pilot is flying the aircraft.
speed brakes
A type of secondary control on a highly streamlined aircraft designed to allow
it to descend rapidly without an excess buildup of airspeed. Speed brakes
produce drag without affecting lift or changing the aircraft’s pitch.
spin
A steep, spiraling descent during which an aircraft is stalled and rotating
rapidly. The characteristic rotation is the result of a strong yawing moment
that occurs when one wing is stalled while the other still produces some lift.
spoilers
Panels on an aircraft's wings that disrupt the flow of air over the wing
surface. Spoilers reduce the wing's lift and increase drag. They enable a jet
aircraft to make a rapid descent without building excess speed. They are also
used immediately after landing to "dump" lift and increase braking
efficiency. Sailplane pilots also use spoilers during descent and landing to
control their rate of descent.
spool up
To increase power in a jet engine.
spot plane
A view in Flight Simulator that allows the user to see the airplane they are
flying as though they were viewing it from another plane flying alongside.
squall
A sudden increase in wind speed by at least 15 knots to a peak of 20 knots or
more and lasting for at least one minute. The essential difference between a
gust and a squall is the duration of the peak speed.
squall line
A narrow band of active, often severe, thunderstorms not associated with a
front. Squall lines often form ahead of a cold front in moist, unstable air, but
they can also develop in unstable air far removed from any front. Squall lines
present the single most-intense weather hazard to aircraft. They usually develop
rapidly and reach maximum intensity during the late afternoon and early evening.
Squall lines may also be too long to fly around and too wide and severe to fly
through, creating a true barrier in the sky.
stability (aircraft)
Generally, a measure of how an object reacts after it is disturbed by an outside
force. Aircraft stability is classified as three types. Positive stability is
the tendency to return to steady-state flight after a change in attitude or
power. Aircraft are generally designed to exhibit positive stability. An
aircraft with neutral stability would remain in the new attitude after being
disturbed and would not return to its initial condition. An aircraft with
negative stability would diverge from its initial condition, with the
oscillations increasing with time.
Stability can also be classified as "static" and "dynamic." Static stability is the initial tendency to return to equilibrium. Dynamic stability refers to the dampening of oscillations over time.
stability(atmospheric)
A measure of the vertical movement of air within an air mass. More specifically,
it is a state of the atmosphere in which the vertical distribution of
temperature is such that a parcel of air resists displacement from its initial
level.
stabilizer
See horizontal stabilizer, vertical stabilizer.
stall
A sudden loss of lift caused by a disruption of the normal smooth flow of air
over the upper surface of a wing. A stall is an aerodynamic phenomenon and has
nothing to do with the engine. A stall occurs when a wing's angle of attack
reaches a specific value, called the critical angle of attack. It is this angle
between the wing and the oncoming air—not the airplane's speed, weight, or
pitch attitude relative to the horizon—that determines when a wing stalls. In
fact, an airplane can stall at any airspeed and in any attitude.
stall speed
The speed at which an aircraft enters a stall under a specified set of
conditions. Although an airplane always stalls when the wing's angle of attack
reaches the critical angle of attack, the speed at which the stall occurs
depends on the aircraft's weight, load factor, the amount of thrust being
produced, angle of bank, position of flaps and landing gear, and other factors.
In fact, an airplane can stall at any airspeed—because regardless of speed, a
stall occurs only when the angle between the relative wind (parallel and
opposite to the aircraft's flight path) and the wing reaches the critical angle
of attack.
standard atmosphere
A hypothetical atmosphere based on climatological averages. The most important
constants defined in the standard atmosphere are: a surface temperature of 15 C
(59 F) and a surface pressure of 1,013.2 millibars (29.92 inches of mercury) at
sea level; a lapse rate in the troposphere of approximately 2 C (3.6 F) per
1,000 feet (6.5 C per kilometer), a drop in pressure of approximately 1 inch of
mercury per 1,000 feet (110 millibars per 1,000 meters), a tropopause of
approximately 36,000 feet (11 kilometers) with a temperature of –56.5 C; and
an isothermal lapse rate in the stratosphere to an altitude of approximately
80,000 feet (24 kilometers).
standard conditions
An arbitrary standard established as a baseline for calculations used in
meteorology, aviation, and aerodynamics. A set of standard conditions exists for
each altitude. At sea level, standard conditions are defined as 29.92 inches of
mercury (1,013 millibars) and 59 F (15 C).
Standard Terminal Arrival Route (STAR)
A published procedure that provides an efficient route for arrival at an airport
while on an IFR flight plan. STARs are designed to facilitate air traffic
control.
Standard Instrument Departure (SID)
A published procedure that provides an efficient route for departure from an
airport while on an IFR flight plan. SIDs are designed to facilitate air traffic
control.
standard pressure
An arbitrary standard established as a baseline for calculations used in
meteorology, aviation, and aerodynamics. A standard pressure is defined at all
altitudes. At sea level, the standard is 29.92 inches of mercury or 1,013
millibars.
standard rate turn
A turn of either 3 degrees or 1.5 degrees per second. Small aircraft typically
use the 3 degrees per second rate, which results in a 360-degree turn after 2
minutes. Large, fast aircraft typically use the slower rate, which results in a
360-degree turn after 4 minutes. Pilots use the standard rate turn while flying
under Instrument Flight Rules (IFR). It provides a steady, predictable, and
easy-to-control rate of turn. Standard rate turns are also useful if the heading
indicator fails. The pilot can make accurate turns to specific headings by
banking at the standard rate and timing the turn.
standard temperature
An arbitrary standard used by aeronautical engineers and pilots in calculations
to determine aircraft performance, true airspeed, true altitude, and so forth.
The standard temperature is part of the definition of the International Standard
Atmosphere (ISA). At sea level, the standard temperature is defined as 59 F (15
C). The standard temperature of dry air drops by about 3.5 F (2 C) per 1,000
feet (305 meters). The standard temperature drops to about 32 F (0 C) at about
7,500 feet (2,300 meters).
standardized instrument cluster
An industry-accepted standard for arranging the six most-commonly used flight
instruments on an aircraft instrument panel. The instruments are arranged in two
rows. The top row contains the airspeed indicator, attitude indicator, and
altimeter. The bottom row contains the turn coordinator, heading indicator, and
vertical speed indicator.
stationary front
A front in which neither air mass is replacing the other. In such cases, the
surface winds tend to blow parallel to the frontal zone. The slope of a
stationary front is normally shallow, although it may be steep, depending on
wind distribution and density difference.
statute mile (sm)
A distance of 5,280 feet (1,609 meters). In the United States, statute miles are
used to measure visibility in weather reports. Speeds and distances are measured
and reported in nautical miles (6,076 feet or 1,852 meters) or nautical miles
per hour (knots).
steady-state flight
Flight in which the opposing pairs of forces (lift and weight, thrust and drag)
are balanced. An aircraft is considered to be in steady-state flight when it
flies at a constant altitude and airspeed, or when it flies at a constant
airspeed and is climbing or descending at a constant rate.
steam fog
Fog formed when air blows from a cold surface (either land or water) over warmer
water.
stick
A tubular control in some aircraft, usually between the pilot’s knees, used to
control the aircraft about its roll and pitch axis (the same function as a
yoke).
stick shaker
A mechanism that shakes the control column in some aircraft to warn the pilot of
an impending aerodynamic stall.
STOL
Abbreviation for "short takeoff and landing." It describes aircraft
capable of operating from airfields with short runways.
stop and go
Similar to a touch and go landing, except the aircraft makes a complete stop.
straight-and-level flight
One of the more difficult maneuvers to master. Like a balancing act,
straight-and-level flight requires that you make smooth, small corrections to
keep from wobbling all over the sky. To master straight-and-level flight, you
must hold a constant altitude and hold a constant heading.
stratiform
Clouds with extensive horizontal development. Stratiform clouds develop in
stable air and, therefore, are composed of small water droplets.
stratocumulus
A low, predominantly stratiform cloud. It is usually a mosaic of gray and
whitish patches or layers. The layers may or may not merge, and such clouds are
rounded or roll-shaped with relatively flat tops.
stratosphere
The region of the earth's atmosphere above the troposphere and tropopause,
beginning at an altitude of 5–10 mi (8–16 km), depending on latitude and
season. The stratosphere is a region of relatively uniform temperatures and
winds, extending to about 30 miles (48 kilometers), where it meets the
mesosphere.
stratus clouds
A low, gray cloud layer or sheet with a fairly uniform base formed in stable
air. Stratus clouds sometimes appear in ragged patches. They seldom produce
precipitation, but may produce drizzle or snow grains.
student pilot certificate
In the United States, a pilot certificate issued to a pilot in training. To be
eligible for a student pilot certificate for powered aircraft, a person must be
at least 16 years old and hold at least a current third-class medical
certificate. A student pilot certificate is valid for 24 months. Student pilots
cannot carry passengers, act as pilot in command of an aircraft for compensation
or hire, or make international flights (except between certain places in Alaska
and Canada). Student pilots can fly only when visibility is at least 3 sm (5 sm
at night) and must maintain visual contact with the ground. Student pilots also
must receive specific endorsements from a certified flight instructor before
flying solo, making cross-country flights, or operating an aircraft in certain
types of controlled airspace. Those endorsements must be renewed every 90 days.
sublimation
The changing of ice directly to water vapor, or water vapor to ice, bypassing
the liquid state in each process. Snow or ice crystals result from the
sublimation of water vapor directly to the solid state.
subsonic
Speeds below the speed of sound, that is, less than Mach 1.
supercharger
A compressor used to increase the density of the air or the air-fuel mixture
supplied to a piston engine. As an aircraft climbs, the density of the air
entering the engine decreases. Without a supercharger or a turbocharger, an
engine gradually loses power. A normally aspirated, or "unboosted,"
engine is most efficient at about 8,000 feet (2,438 meters). By the time an
aircraft reaches 18,000 feet (5,486 meters), the density of the air is about
half its value at sea level, and a supercharger or turbocharger is required for
efficient operation of the engine.
supercooled water
Water droplets colder than 0 C (32 F). When supercooled droplets strike an
exposed object, such as an aircraft's wings and other structures, the impact
induces freezing. Supercooled water droplets often are in abundance in clouds at
temperatures between 0 and –15 C with decreasing amounts at colder
temperatures. However, strong vertical currents may carry supercooled water to
great heights where temperatures are much colder. Supercooled water has been
observed at temperatures colder than –40 C.
supersonic
Speed that exceeds the speed of sound; Mach 1 or greater.
surface inversion
An inversion with its base at the surface, often caused by cooling of the air
near the surface as a result of terrestrial radiation, especially at night.
surface visibility
Visibility observed from eye-level above the ground.
synchrophaser
A device that automatically adjusts the speed of the propellers of all engines
on a multiengine aircraft so that a master blade on each propeller keeps the
same relative position in its rotation to the master blade of each of the other
propellers.
Propellers out of synch result in higher cabin-noise levels and a sort of washing-machine-like sound. During World War II, pilots flying with their props out of synch earned the nickname "Washing Machine Charlie."
tachometer
The instrument that shows the speed of rotation of the engine. It is marked in
revolutions per minute (rpm). Engines that produce more than about 180
horsepower usually have constant-speed propellers that can change the blade
angle to make more efficient use of engine power throughout a wide range of
airspeeds.
taildragger
An aircraft that has its main wheels mounted ahead of the center of gravity and
a small pivoting or steerable wheel supporting the aft fuselage. There is no
nosewheel, as with tricycle-gear aircraft. Taildraggers were the norm during the
early years of aviation and are sometimes referred to as conventional-gear
aircraft. They are trickier to handle on the ground than tricycle-gear aircraft
and require special training and skill.
tailwind
A wind that blows in the same direction as the aircraft is traveling.
takeoff roll
The portion of the takeoff during which the airplane accelerates on the runway.
taxi
To move an aircraft under its own power on the ground.
temperature layer
In Flight Simulator, a user-specified weather option that includes the air
temperature at a specific altitude and the day-night variation in temperature.
You select temperature options in the Advanced Weather dialog box. You can
create four temperature layers to see how temperature affects density altitude
and aircraft performance.
temperature-dew point spread
The difference between air temperature and dew point temperature. As this
difference narrows, clouds and fog are more likely to appear. Pilots must also
be aware that even if the spread at ground level is quite large, as temperature
drops with altitude, the spread narrows, and clouds may form. Pilots should be
especially alert for fog whenever the temperature-dew point spread is 5 F (2.8
C) or less and decreasing.
terminal velocity dive brakes
See spoilers.
tetrahedron
A large wind-direction indicator made of lightweight material in the shape of
pyramid.
thermal
A rising column of air caused by the sun heating the earth's surface. Sailplane
pilots use thermals to climb or maintain altitude.
threshold
The beginning of the runway surface that is usable for landings. The threshold
may coincide with the physical end of the runway or be displaced if part of the
runway is not usable for landings. The threshold is marked by a single white
line on visual runways or by eight parallel white lines arranged in two groups
of four on either side of the centerline of an instrument runway.
throttle
The cockpit control that most directly determines the power output of the
engine. In a piston engine, the throttle actually controls the amount of air
entering the carburetor or induction system. The carburetor, or fuel metering
system, mixes the appropriate amount of fuel with the air to create a
combustible mixture. When fully "open," the throttle allows the
maximum amount of air to enter the system to produce maximum power. When the
throttle is "closed," only a small amount of air enters the system and
the engine produces minimum power.
thrust
The forward force generated by a propeller or jet engine that moves the aircraft
forward through the air. One of the four major forces, thrust is opposed by
drag.
thunderstorm
In general, a local storm invariably produced by a cumulonimbus cloud and always
accompanied by lightning and thunder.
tie-down
The spot on an airport ramp where an aircraft is parked and secured with ropes
or chains. Airplanes are designed to fly, so they must be tied down to prevent
catastrophe in windy weather.
tilt-rotor
A vertical-takeoff aircraft with rotors that can tilt from the horizontal to the
vertical. An example of this type of aircraft is the V-22 Osprey.
torque
A force that produces or attempts to produce rotation.
touch and go
A landing during which the aircraft does not come to a complete stop before
power is applied and the aircraft takes off again. Often done for pilot practice
and training.
tower
A building on an airport from which an air traffic controller directs traffic
within the immediate airport traffic area. The top of the tower, called a cab,
is usually glassed in on all sides giving a 360-degree view.
tower visibility
Prevailing visibility determined from the control tower.
towering cumulus
A rapidly growing cumulus in which height exceeds width.
trace icing
Icing, regardless of type, that accumulates at about the same rate as it
dissipates by sublimation. Trace icing is not considered hazardous, even to
aircraft without anti-icing or deicing equipment, unless the airplane remains in
icing conditions for more than one hour.
track
The path followed by an aircraft while in flight.
trade winds
Prevailing, almost continuous, winds blowing with an easterly component from the
subtropical high pressure belts toward the intertropical convergence zone. They
blow northeast in the Northern Hemisphere, southeast in the Southern Hemisphere.
traffic
Aircraft other than yours that present a potential for occupying the same
airspace.
traffic pattern
The traffic flow prescribed for aircraft landing at and taking off from an
airport. Also called a "circuit" in Britain. A complete landing
pattern includes a downwind leg, a base leg, and a final leg. Aircraft taking
off typically fly an upwind leg and crosswind leg to depart the airport traffic
pattern.
trainer
Aircraft used for pilot training. They are usually (not always) single-engine
light aircraft. Popular models for pilot training include the Cessna 152, 172,
and 182.
transmissometer
An instrument system that measures the transmission of light through the
atmosphere. The transmission value is converted either automatically or manually
into visibility, runway visual range (RVR), or both.
translating tendency
The tendency of a helicopter to drift in the direction of the tail rotor thrust.
transonic
Speeds close to the speed of sound in which both subsonic and supersonic airflow
conditions exist. Transonic speeds range from about Mach 0.8 to Mach 1.4.
transponder
An airborne transceiver that receives signals from air traffic control (ATC)
radar and replies with a preset identification code, or "squawk," set
by the pilot. A computer uses the code to display information about each
aircraft on an air traffic controller's radar display. Most aircraft today are
also equipped with altitude encoders, which transmit the aircraft's altitude
along with the transponder code. In the United States, aircraft operating under
visual flight rules (VFR) squawk code 1200 unless they are using air traffic
control services and are assigned a specific code by ATC. Under instrument
flight rules (IFR), all aircraft are assigned transponder codes by ATC.
transverse flow effect
A decrease in lift in the aft portion of a helicopter rotor disk when in forward
flight or hovering in a wind.
tricycle-gear
A landing gear system that includes a nosewheel assembly and two main gear
assemblies. Because the center of gravity of a tricycle-gear airplane lies ahead
of the main gear, this geometry is much more stable on the ground than the
so-called conventional gear or "taildragger" arrangement, which has
two main gear assemblies and a tailwheel.
trim
To adjust a movable tab on a control surface, usually the elevator, to relieve
pressure on the flight controls. Trim is necessary because as an aircraft
changes speed, the amount of air flowing over the control surfaces varies.
Without trim, a pilot would have to hold forward or back pressure on the yoke or
column to maintain a specific airspeed or pitch attitude. Larger aircraft also
have aileron and rudder trim.
tropopause
A thin layer in the upper atmosphere that forms the boundary between the
troposphere and stratosphere. The tropopause is usually characterized by an
abrupt change in lapse rate. The height of the tropopause varies from about
65,000 feet (19.8 kilometers) over the equator to 20,000 feet (6,096 meters) or
lower over the poles. Temperature and wind vary greatly in the vicinity of the
tropopause. Maximum winds generally occur at levels near the tropopause. These
strong winds create narrow zones of wind shear, which often generate hazardous
high-altitude turbulence.
troposphere
The layer of the atmosphere from the surface to an average altitude of about 7
miles (11 kilometers). Most weather occurs within the troposphere. Temperature
generally decreases with altitude in the troposphere at an average rate of 2 C
(3.6 F) per 1,000 feet (305 meters). The height of the troposphere varies with
latitude and seasons. It slopes from about 20,000 feet (6,096 meters) over the
poles to about 65,000 feet (19.8 kilometers) over the equator. It is higher in
summer than in winter. A very thin layer called the tropopause marks the
boundary between the troposphere and the next highest layer, the stratosphere.
trough
In meteorology, an elongated area of relatively low atmospheric pressure. A
trough is usually associated with and most clearly identified as an area of
maximum cyclonic curvature of the wind flow.
true airspeed (TAS)
An aircraft's actual speed through the surrounding air. As an aircraft climbs,
the surrounding air becomes less dense. Therefore, indicated airspeed tends to
decrease as altitude increases. To determine how fast the airplane is really
moving through the air, the pilot calculates TAS based on the aircraft's current
pressure altitude and the outside air temperature. A pilot must know TAS to
solve navigation problems and file flight plans. As a rule of thumb, at a given
indicated airspeed, true airspeed increases about 2 percent for each 1,000 feet
(305 meters) of altitude. Therefore, an aircraft flying at an indicated airspeed
of 100 knots at 10,000 feet (3,050 meters) is actually flying at about 120 knots
through the air.
true altitude
An aircraft's actual height above mean sea level. True altitude is the altitude
shown on the altimeter, corrected for nonstandard temperature. If the
temperature at a particular indicated altitude is warmer than the standard
temperature for that altitude, an aircraft's altimeter senses higher-than-normal
pressure and shows an altitude lower than the aircraft is actually flying. If
the temperature is cooler than the standard temperature for a particular
altitude, the altimeter senses lower-than-normal pressure and shows an altitude
higher than the aircraft is actually flying. Variations from nonstandard
temperature usually cause only small errors in the altimeter. When flying
without visual references over mountainous terrain, however, or when
temperatures aloft differ significantly from the standard temperatures, a pilot
should check the aircraft's true altitude to ensure obstacle clearance.
true north
A heading, or course, pointed directly at the earth's geographic North Pole. The
earth's magnetic North Pole is offset from the geographic North Pole, so course
lines drawn on a chart are usually referenced to lines of longitude, which
indicate true north. To solve navigation problems, pilots convert true courses,
or headings, into magnetic courses and headings that they can fly by referencing
the aircraft's compass. The difference between true north and magnetic north is
called "variation." The actual value of the variation depends on your
location. Many weather reports and forecasts indicate wind direction in
reference to true north.
turbine
The fan-like portion of a jet engine or turboprop engine that compresses the
incoming air.
turbine inlet temperature (TIT)
Air temperature measured as it enters the turbine inlet guide-vanes or the first
stage of a turbocharger or a turbine engine. TIT is the highest temperature
inside a turbocharged engine and is a limiting factor of the amount of power an
engine can produce.
turbocharger
A device on a piston engine that compresses the air entering the engine to
maintain power output at high altitudes. Exhaust gas from the engine spins a
turbine in the turbocharger at high speed. A compressor attached to the same
shaft as the turbine compresses the air entering the intake manifold,
"boosting" the engine's power as the density of the outside air
decreases with altitude. Turbochargers increase the temperature of the air
entering the engine, so pilots must monitor engine temperatures carefully.
turbofan
A jet engine in which most of the air entering the engine is accelerated by a
large fan and does not pass through the combustion chamber of the engine.
Turbofan engines have largely replaced turbojet engines, in which most of the
air entering the engine passes through the combustion chamber. Turbofan engines
are much more efficient and significantly quieter than turbojets.
turbojet
A jet engine in which most of the air entering the engine passes through several
compressing turbines and then enters the combustion chamber. In a turbojet
engine, the exhaust stream produces most of the engine's thrust. Turbojet
engines have largely been replaced by more efficient and quieter turbofan
engines.
turboprop
A jet engine that drives a propeller to create thrust. Turboprop aircraft are
less noisy and burn less fuel than turbojet aircraft, but they are also
efficient only at speeds up to about 640 kilometers per hour (400 mph). Also
called a propjet.
turn coordinator
One of the six primary flight instruments, the turn coordinator shows the rate
of turn and the quality of a turn—whether the aircraft is slipping, skidding,
or in a balanced turn. In most modern light aircraft, the turn coordinator has
replaced the "needle and ball," which served the same function.
TWEB
Abbreviation for "transcribed weather broadcast." These recorded
weather reports and forecasts, prepared by a Flight Service Station (FSS) in the
United States, are broadcast over many navigation facilities, especially VORs.
Pilots can monitor TWEB broadcasts while en route to stay up-to-date with the
latest weather information.
type certificate
An official document that certifies that an aircraft or engine design has met
all the criteria specified in the regulations governing the certification and
testing of aircraft. In the United States, the FAA issues normal, utility,
transport, aerobatic, experimental, limited, restricted, and provisional type
certificates.
type rating
In the United States, an authorization added to a pilot certificate that permits
a person to act as pilot in command of a specific type of aircraft, usually a
heavy, turbojet-powered, or rotary wing aircraft. Type ratings are required for
all aircraft with a maximum certified takeoff weight of more than 12,500 pounds
(5,670 kilograms) and all turbojet-powered aircraft, regardless of maximum
takeoff weight. A type rating is also required to act as pilot in command of a
helicopter if the operation also requires that the pilot hold an airline
transport pilot certificate.
ultralight
Single-seat, lightweight aircraft designed for recreational flying. Also known
as "microlights" in Britain. In the United States, ultralight aircraft
are not certified by the FAA and no pilot certificate is required to fly them.
According to United States regulations (FAR Part 103), an aircraft qualifies as
an ultralight if it has an empty weight of no more than 254 pounds(115
kilograms), if it is equipped with an engine, can carry no more than 5 gallons
(18.9 liters) of fuel, cannot fly more than 55 knots in level flight at full
power, and has a power-off stall speed no greater than 24 knots.
uncontrolled airspace
Airspace in which air traffic control does not provide services and in which an
ATC clearance is not required to operate, regardless of weather conditions.
uncoordinated flight
Slipping or skidding flight caused by yawing forces produced by a turn, by the
action of the propeller and slipstream, or by an imbalance of power in a
multiengine aircraft. The inclinometer (ball) of the turn coordinator shows
whether the yawing forces are properly balanced. If the ball is on the inside of
a turn, the airplane is slipping. If the ball moves to the outside of a turn,
the airplane is skidding.
under the hood
See hood.
undercast
A solid cloud layer as viewed from above the layer.
UNICOM
A privately owned radio station on an airport used to give advisories to pilots.
UNICOM cannot be used to control traffic.
updraft
A localized upward current of air.
upslope fog
Fog formed when air flows upward over rising terrain and is cooled to or below
its initial dew point. Once the upslope wind ceases, the fog dissipates. Unlike
radiation fog, upslope fog can form under cloudy skies. It often is quite dense
and extends to high altitudes.
upwind
That leg of a standard traffic pattern aligned with the runway on takeoff. The
aircraft is said to be on the upwind leg until it is turned 90 degrees onto the
crosswind leg.
useful load
The maximum allowable weight of an aircraft minus its empty weight. The useful
load includes the weight of the fuel, oil, crew, passengers and their baggage,
and any cargo carried.
UTC (Universal Coordinated Time)
The official time used in air navigation. Also known as Zulu time, or Greenwich
Mean Time (GMT). UTC is based on the 24-hour clock; for example, 6 P.M. is 1800
hours. Departure and arrival times, air traffic control clearances, the valid
time of weather reports and forecasts, and other time-sensitive information in
aviation is expressed in UTC.
vector
A heading given by an air traffic controller to a pilot for the purpose of
navigation or traffic avoidance.
vertical axis
An imaginary vertical line running through the center of an aircraft. Rotation
about the vertical axis is called "yaw" and is controlled by the
rudder.
vertical speed indicator
One of the six basic flight instruments, the vertical speed indicator shows an
aircraft's rate of climb or descent, usually in feet per minute. Also known as
the rate of climb indicator (RCI) or vertical velocity indicator (VVI). Large
aircraft are typically equipped with a sophisticated version of this instrument,
called an "instantaneous vertical speed indicator" (IVSI) that reacts
immediately to changes in altitude.
vertical stabilizer
The vertical tail surface on an aircraft; sometimes called a "fin."
The vertical stabilizer is fixed on most aircraft. With the attached rudder, the
vertical stabilizer provides directional stability by controlling movement about
the vertical (yaw) axis.
vertigo
A state of temporary spatial confusion resulting from misleading information
sent to the brain by various sensory organs; also called "spatial
disorientation." Vertigo typically occurs when a pilot cannot see the
ground or other references due to clouds or darkness. Turns and other maneuvers
can cause the vestibular system—a set of tubes and other sensory organs in the
inner ear—to send conflicting signals about the aircraft's orientation and
movement. Without visual references to overcome those sensations, the pilot
quickly becomes disoriented and unable to tell whether the airplane is flying
straight and level, turning, climbing, or descending. To avoid or overcome
vertigo, a pilot must rely on the flight instruments to verify the aircraft's
attitude and maintain control.
very high frequency (VHF)
The portion of the radio spectrum used in civil aviation for primary radio
navigation and communications. Voice communications are assigned frequencies
between 118.0 and 136.975 MHz. VORs operate on frequencies between 108.0 and
177.95 MHz.
very high frequency omnidirectional radio (VOR) range
A ground-based radio transmitter that sends signals in 360 radials. Some of
these radials define airways, but pilots can track any radial to fly a specific
path over the ground. VORs operate on frequencies between 108.0 to 177.95 MHz in
the VHF band. Although satellite-based navigation systems are rapidly coming
into widespread use, VORs still remain the primary electronic navigation system
in use today.
VFR sectional charts
Navigational charts published for use by pilots flying under visual flight rules
(VFR). The charts depict navaids, landmarks, Victor airways, terrain elevations,
and other important information relevant to VFR flight.
Victor airways
Airways delineated by navigational radio signals for low routes (below 18,000
feet). Sometimes referred to as highways in the sky. Jet airways are used for
high-altitude routes.
view-limiting device
See hood.
virga
Water or ice particles falling from a cloud, usually in wisps or streaks, that
evaporate before reaching the ground.
virtual airline
Airlines created on the World Wide Web by and for pilots of flight simulators.
Virtual airlines simulate the world of commercial aviation by hiring, training,
and assigning routes to virtual pilots. There has been a great increase in
interest in these airlines in recent years, and some operations are quite
elaborate.
visibility
The ability to see and identify prominent, unlighted objects by day and
prominent, lighted objects at night. Visibility is expressed in units of
distance (statute miles, hundreds of feet, or meters). Atmospheric conditions
determine the distance.
visual approach slope indicator
A lighting system that indicates an airplane's position relative to the desired
glideslope to a particular runway.
visual flight rules (VFR)
The "rules of the road" that govern flight when the visibility and
ceiling allow pilots to navigate and avoid obstacles and other aircraft by
visual reference. In the United States, VFR flight is generally permitted when
the visibility is at least 3 miles (5 kilometers) and a pilot is able to operate
at a safe altitude that is at least 500 ft (152 meters) below and 1,000 feet
(304 meters) above any clouds. In addition, the pilot must remain at least 2,000
feet (608 meters) horizontally from any clouds. Specific requirements for VFR
depend on the type of airspace, time of day, and height above the terrain.
visual meteorological conditions
Weather conditions that permit flight under visual flight rules (VFR). In
controlled airspace in the United States, VMC conditions generally mean that the
ceiling is at least 1,000 feet (305 meters) and flight visibility is at least 3
miles (5 kilometers).
VOR approach
A nonprecision instrument approach in which a VOR is the initial approach fix.
VOR hold
A holding pattern over a VOR station.
VOR intercept
Tuning in, identifying, and turning toward a VOR station.
vortices
Rotating air currents created by wings and other airfoils that are producing
lift. Vortices are typically created when high-pressure air below a wing
circulates toward the low-pressure area above a wing. These vortices are the
primary source of induced drag, a by-product of lift. Vortices created by large,
heavy aircraft (called "wake turbulence") are a serious hazard to
smaller aircraft, especially during takeoff and landing.
V-speeds
Used to designate speeds during specific flight conditions.
VTOL
Abbreviation for "vertical takeoff and landing," describing aircraft
that can take off straight up and land straight down without the need of a
runway. The most successful application of VTOL technology, based on the
vectored-thrust engine, is the British Harrier jump jet.
Wagstaff, Patty
1951– . American aerobatic pilot. Wagstaff was the 1993 International
Aerobatic Club Champion and a three-time United States National Aerobatic
Champion. A member of the United States Aerobatic Team, she is also an
aerobatics coach, an aerial competition judge, and a movie stunt pilot.
wake turbulence
Turbulence caused by a moving aircraft. More specifically, the powerful vortices
generated by the wing tips of a large, heavy aircraft.
warm front
Any nonoccluded front in which warmer air replaces colder air.
waypoint
A predetermined navigational point in space along a route of flight. Waypoints
can be electronically stored in some navigation devices, such as RNAV and GPS
units.
weather areas
In Flight Simulator, regions with similar weather characteristics. Flight
Simulator has a global weather area, and you can create two local weather areas.
You can define the size of the local weather areas and specify the type of
clouds, visibility, temperature, wind, atmospheric pressure, and other
characteristics of each area.
weathercock
(Verb) To display a tendency to veer in the direction of the wind.
weathervane effect
The tendency of an aircraft to pivot around its center of gravity and point into
the wind.
weight
One of the four basic forces at work on an aircraft in flight. Lift opposes
weight (more accurately, the sum of all downward forces), which always acts
directly toward the center of the earth. In most calculations, aeronautical
engineers assume that all of an aircraft's weight is concentrated at a point
called the center of gravity.
wet wing
An aircraft wing in which fuel is stored directly inside the skin of the wing as
opposed to enclosing the fuel in a rubber bladder inside the wing.
Whitcomb, Richard
1921– American engineer. At the laboratory of the National Advisory Committee
for Aeronautics (NACA), Whitcomb developed the "area rule" for
reducing drag at transonic speeds by pinching the fuselage where it meets the
wing. In 1955, he won aviation's prestigious Collier Trophy for inventing this
"Coke-bottle effect" during his breakthrough redesign of the fuselage
of the Convair YF-102.
Whittle, Frank
1907–1996. English engineer and RAF officer who invented the turbojet aircraft
engine. Whittle published his theory of jet propulsion in 1928, but the British
Air Ministry didn't become interested in the idea until 1938. Whittle developed
a working jet aircraft by 1941; however, it wasn't until 1944 that the first
military jet aircraft, the Gloster Meteor, was put into service.
wilco
Used in radio transmissions as shorthand for "will comply."
wind layer
In Flight Simulator, a user-specified weather option that includes wind speed,
direction, gust factor, and turbulence between two altitudes. You select these
options on the Wind tab in the Advanced Weather dialog box. You can create two
wind layers in each weather area.
wind shear
A sudden, sharp change in wind direction or speed, often associated with a
violent, downward burst of air called a microburst or a low-level temperature
inversion. Wind shear is particularly dangerous to aircraft during takeoff and
landing, where it can cause large variations in airspeed and lead to a rate of
sink that can push an aircraft into the ground.
wind tunnel
A device for studying the effects of airflow on aircraft and other vehicles or
structures. To simulate the conditions of flight, an aircraft model is mounted
in the tunnel and subjected to a stream of air. Sensors gather data on lift and
drag, pressure, and other forces acting on the model.
wing loading
An aircraft's weight divided by the area of its wings. For example, an aircraft
weighing 4,000 pounds (1,814 kilograms) that has 400 square feet of wing area
has a wing loading of 10 pounds per square foot.
winglets
Vertical extensions added to the ends of a main wing. Winglets reduce induced
drag by increasing the effective aspect ratio of the wing, thereby decreasing
the intensity of wingtip vortices produced as a by-product of lift.
wingspan
The distance from one wing tip to the other.
wingtip vortex
Rapidly rotating air at an aircraft's wing tips created when a wing produces
lift. At the tips, high-pressure air below the wing spirals up to the
low-pressure area above the wing. Large, heavy aircraft produce intense vortices
that are extremely hazardous to small aircraft, especially during takeoff and
landing. For example, a small aircraft that flies into a wingtip vortex can be
rolled inverted because the rotation of the vortex exceeds the rolling
capability produced by the ailerons. Also known as "wake turbulence."
Wright brothers
American aviation pioneers Wilbur (1867–1912) and Orville (1871–1948) Wright
made the first powered flight in a heavier-than-air craft. They began
experimenting with double-winged kites and gliders, and in 1900, made their
first test flights at Kitty Hawk. In 1901, they built the first wind tunnel in
the United States, testing over 200 models of wing surfaces. After building an
engine for their Flyer, they made their historic flight on December 17, 1903.
yaw
Movement of an aircraft about its vertical axis, as when the nose turns left or
right. Along with roll and pitch, yaw is one of an airplane's three basic
movements. The vertical stabilizer and rudder are designed to control yaw.
Yeager, Chuck
1923– American Air Force officer and fighter pilot, test pilot, and the first
person to fly faster than the speed of sound (1947). Yeager, who achieved the
rank of brigadier general in 1968, received numerous decorations, including the
Distinguished Service Medal, the Purple Heart, and the Presidential Medal of
Freedom. Yeager made his most famous flight despite two broken ribs he sustained
in a riding accident just days before.
yoke
See control yoke.
zeppelin
An airship with rigid internal bracing. The helium or hydrogen used to lift a
zeppelin is usually contained in large cells. The largest of airships, zeppelins
were used as bombers in World War I, but they caused little damage; instead,
most were lost to accidents and enemy fire. In 1937, the "Hindenburg"
disaster brought a swift end to the use of the rigid airship as a civil
transport.
Zeppelin, Count Ferdinand von
1838–1917. German aeronaut, inventor, and army general who rode in observation
balloons with Union forces during the American Civil War. In 1898, he founded an
airship factory in Germany and constructed the first rigid type of airship. By
1910, his zeppelins carried passengers on excursions between German cities, and
in 1912, the German navy ordered the first military zeppelin.
Zulu time
See Greenwich Mean Time.