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Glossary of Terms

Above Ground Level (AGL)
Actual height above the surface of the earth, either land or water.

Absolute Altitude
Actual height above the surface of the earth, either land or water; commonly referred to as height above ground level (AGL).

Absolute Ceiling
The altitude where a particular airplane's climb rate reaches zero.

Accident
An occurrence that causes serious injury or death, or substantial damage to an aircraft.

Aileron
Control surfaces on the trailing edge of the wing. Ailerons on each side of the airplane deflect in opposite directions to control the roll, or bank, of the aircraft. Movement of the ailerons is controlled by either the control yoke or sidestick. A trim system minimizes the force needed to hold the ailerons in the proper position for various flight conditions.

Air Carrier
A person who undertakes directly, by lease or other arrangement, to engage in air transportation.

Air Circulation System
The aircraft system that using fresh air, conditions and distributes this air throughout the aircraft. This air is used to power pneumatic systems and pressurize the aircraft, as well as heat and cool the passenger cabin and some of the cargo compartments.

Air Defense Identification Zone (ADIZ)
The area of airspace over land or water that extends upward from the surface and within which the ready identification, the location and the control of aircraft are required in the interest of national security.

  • Domestic Air Defense Identification Zone (ADIZ) An ADIZ within the United States along an international boundary of the United States.
  • Coastal Air Defense Identification Zone An  ADIZ over the coastal waters of the United States.
  • Distant Early Warning Identification Zone (DEWIZ) An ADIZ over the coastal waters of the state of Alaska. ADIZ locations and operating and flight plan requirements for civil aircraft operations are specified in FAR Part 99.

Air Route Traffic Control Center (ARTCC)
or En Route Center A facility established to provide air traffic control service to aircraft operating on IFR flight plans within controlled airspace and principally during the en route phase of flight. When equipment capabilities and controller workload permit, certain advisory/assistance services may be provided to VFR aircraft.

Air Taxi
An aircraft operator who conducts operations for hire or compensation in accordance with FAR Part 135 in an aircraft with 30 or fewer passenger seats and a payload capacity of 7,500 pounds or less. An air taxi operates "on-demand" and does not meet the "flight scheduled" qualifications of a commuter.

Air Traffic Control (ATC)
A service operated by the appropriate authority to promote the safe, orderly and expeditious flow of air traffic.

Aircraft Certification Systems Evaluation Program (ACSEP)
FAA ACSEP teams perform safety audits on manufacturers and suppliers. The program monitors aviation safety performance and ensures continued operational safety of aircraft by providing a systematic and consistent evaluation of compliance with prescribed safety standards, maximizing cooperation with industry; and identifying technological trends that require development of new or revised regulations, policy, guidance, and training.

Airfoil
Any surface such as an aileron, propeller, wing or rudder that controls an aircraft’s lift, stability, direction, thrust or propulsion as air moves past the surface.

Airport
An area on land or water that is used or intended to be used for the landing and takeoff of aircraft and includes its buildings and facilities, if any.

Airport Advisory Area
The area within 10 statute miles of an airport where a flight service station is located, but where there is no control tower in operation.

Airport Surveillance Radar (ASR)
Approach and departure control radar used to detect and display an aircraft's position in the terminal area and to provide aircraft with range and azimuth information.

Airport Traffic Control Tower (ATCT)
A terminal facility that uses air/ground communications, visual signaling, and other devices to provide ATC services to aircraft operating in the vicinity of an airport or on the movement area. The ATCT authorizes aircraft to land or takeoff at the airport controlled by the tower or to transit the Class D airspace area regardless of flight plan or weather conditions IFR or VFR). A tower also may provide approach control services (radar or nonradar).

Airspace
see Class A Airspace, Class B Airspace, Class C Airspace, Class D Airspace, Class E Airspace or Class G Airspace

Airspeed
see Indicated Airspeed (IAS), Calibrated Airspeed (CAS), True Airspeed (TAS)

Airworthiness
A term used to describe both the legal and mechanical status of an aircraft with regard to its readiness for flight.

Airworthiness Directive (AD)
An FAA order mandating aircraft inspection, maintenance or modification.

Alert Area
Special use airspace which may contain a high volume of pilot training activities or an unusual type of aerial activity.

Alpha
The phonetic alphabet word for the letter A.

Altimeter
A pressure-sensing instrument that displays the altitude of an aircraft above the mean sea level (MSL).

Altimeter Setting
The barometric pressure setting used to adjust a pressure altimeter for variations in existing atmospheric pressure and temperature.

Altitude
The height expressed in units of distance above a reference plane, usually above mean sea level or above ground level.

Angle of Attack
The angle between a wing and the relative wind.

Anti-icing fluid
A gel-like fluid designed to remove frozen contamination from an aircraft and prevent re-contamination by frost, snow or ice. See Type 1, Type 2, Type 3, Type 4

Artificial Horizon
An instrument that enables a pilot to determine the attitude of the aircraft in relation to the horizon i.e., whether the aircraft is nose-up, nose-down, or banking left or right.

Attitude
An aircraft's position in relation to the horizon (i.e., whether the aircraft is flying level, nose up, nose down, or banking left or right).

Automated Surface Observation System (ASOS)
Weather reporting system which provides surface observations every minute via digitized voice broadcasts and printed reports.

Automated Weather Observation System (AWOS)
Automated weather reporting system consisting of various sensors, a processor, a computer-generated voice subsystem and a transmitter to broadcast local, minute-by-minute weather data directly to the pilot.

Automatic Direction Finder (ADF)
An aircraft radio navigation system which senses and indicates the direction to a low/medium frequency (L/MF), nondirectional radio beacon (NDB) or commercial broadcast station.

Automatic Terminal Information Service (ATIS)
A prerecorded continuous broadcast information service provided by ATC at high- activity terminal areas. Provides a repetitive transmission of essential but routine information, such as weather, visibility and runway information.

Autopilot
A gyroscope-controlled device that, when programmed by a pilot, can keep an aircraft in a predetermined flight path.

Auxiliary Power Unit (APU)
A small jet engine used to start the main engines and provide power to the aircraft while on the ground. In most aircraft, the APU can be used for backup power during flight.

Available Seat Mile (ASM)
One seat flown one mile. An airliner with 100 passenger seats, flown a distance of 100 miles, represents 10,000 available seat miles (ASMs).

Aviation Trust Fund
Fund established by Congress to pay for improvements to the nation's airports and air traffic control system. Money in the fund comes solely from users of the system - primarily a tax on domestic airline tickets.

Avionics
The computers and other electronic systems that monitor and control an aircraft's electrical and mechanical systems.

Azimuth
The direction or angle between the radar site and an aircraft; measured clockwise from north in a horizontal plane.

Bearing
The horizontal direction to or from any point, usually measured clockwise from true north (true bearing) magnetic north (magnetic bearing), or some other reference point, through 360o.

Best Angle-of-Climb Airspeed (Vx)
Produces the greatest gain in altitude for horizontal distance traveled.

Best Rate-of-Climb Airspeed (Vy)
Produces the maximum gain in altitude per unit of time.

Bravo
The phonetic alphabet word for the letter B.

Calibrated Airspeed (CAS)
Indicated airspeed of an aircraft, corrected for installation and instrument errors.

Camber
The curve of an airfoil section from the leading edge to the trailing edge.

Captain
Commands the aircraft and is responsible for safety; requires an air transport pilot (ATP) certificate.

Cargo
Anything other than passengers, carried for hire, including both mail and freight.

Category
(1) As used with respect to the certification, ratings, privileges and limitations or airmen, means a broad classification of aircraft (airplane, rotorcraft, glider and lighter-than-air).(2) As used with respect to the certification of aircraft, means a grouping of aircraft by intended use or operating limitations (transport, normal, utility, acrobatic, limited, restricted and provisional).

Ceiling
The height above the earth’s surface of the lowest layer of clouds or obscuring phenomena that is reported as broken, overcast or obscuration, and not classified as thin or partial.

Center
An Air Route Traffic Control Center (ARTCC).

Center of Gravity (CG)
The theoretical point where the entire weight of the airplane is considered to be concentrated.

Certificated Airport
An airport operating under FAR Part 139. The FAA issues airport operating certificates to all airports serving scheduled or unscheduled air carrier aircraft designed for more than 30 passenger seats. Certificated airports must meet minimum safety standards in accordance with FAR Part 139.

Charlie
The phonetic alphabet word for the letter C.

Class
(1) As used with respect to the certification, ratings, privileges and limitations of airmen, means a classification of aircraft within a category having similar operating characteristics (single engine, multi-engine, land, water, gyroplane, helicopter, airship and free balloon). (2) As used with respect to certification of aircraft, means a broad grouping of aircraft having similar characteristics of propulsion, flight or landing (airplane, rotorcraft, glider, balloon, landplane and seaplane).

Class A Airspace
(formerly PCA - Positive Control Area) Generally, that airspace from 18,000 feet MSL up to and including flight level (FL) 600 (60,000 feet pressure altitude), including the airspace overlying the waters within 12 nautical miles of the coast of the 48 contiguous United States and Alaska. Unless otherwise authorized, all persons must operate their aircraft under IFR in this airspace. For specific designations and descriptions of the airspace classes, please refer to FAR Part 71.

Class B Airspace
(formerly TCA - Terminal Control Area) Generally, that airspace from the surface to 10,000 feet MSL surrounding the nation's busiest airports in terms of airport operations or passenger enplanements. The configuration of each Class B airspace area is individually tailored and consists of a surface area and two or more layers (some Class B airspace areas resemble upside down wedding cakes), and is designed to contain all published instrument procedures once an aircraft enters the airspace. An ATC clearance is required for all aircraft to operate in the area, and all aircraft that are so cleared receive separation services within the airspace. The cloud clearance requirement for VFR operations is "clear of clouds." For specific designations and descriptions of the airspace classes, please refer to FAR Part 71.

Class C Airspace
(formerly ARSA - Airport Radar Service Area) Generally, that airspace from the surface to 4,000 feet above the airport elevation [charted in MSL] surrounding those airports that have an operational control tower, are serviced by a radar approach control, and that have a certain number of IFR operations or passenger enplanements. Although the configuration of each Class C Airspace area is individually tailored, usually consists of a surface area with a five nautical mile (NM) radius, an outer circle with a 10 NM radius that extends from 1,200 feet to 4,000 feet above the airport elevation, and an outer area. Each person must establish two-way radio communications with the ATC facility providing air traffic services prior to entering the Class C Airspace and thereafter maintain those communications while within the airspace. VFR aircraft are only separated from IFR aircraft within the airspace. For specific designations and descriptions of the airspace classes, please refer to FAR Part 71.

Class D Airspace
(formerly ATA - Airport Traffic Area and CZ Control Zone) Generally, that airspace from the surface to 2,500 feet above the airport elevation [charted in MSL] surrounding those airports that have an operational control tower. The configuration of each Class D airspace area is individually tailored and when instrument procedures are published, the airspace normally will be designed to contain the procedures. Arrival extensions for instrument approach procedures may be Class D or Class E airspace. Unless otherwise authorized, each person must establish two-way radio communications with the ATC facility providing air traffic services prior to entering the airspace and thereafter maintain those communications while in the airspace. No separation services are provided to VFR aircraft. For specific designations and descriptions of the airspace classes, please refer to FAR Part 71.

Class E Airspace
(formerly General Controlled Airspace) Generally, if the airspace is not Class A, Class B, Class C or Class D, and it is controlled airspace, it is Class E airspace. Class E airspace extends upward from either the surface or a designated altitude to the overlying or adjacent controlled airspace. When designated as a surface area, the airspace will be configured to contain all instrument procedures. Also in this class are Federal airways, airspace beginning at either 700 or 1,200 feet AGL used to transition to/from the terminal or en route environment, en route domestic and offshore airspace areas designated below 18,000 feet MSL. Unless designated at a lower altitude, Class E airspace begins at 14,500 feet MSL over the United States, including that airspace overlying the waters within 12 nautical miles of the coast of the 48 contiguous states and Alaska, up to, but not including 18,000 feet MSL, and the airspace above flight level (FL) 600. For specific designations and descriptions of the airspace classes, please refer to FAR Part 71.

Class G Airspace
Airspace that has not been designated as Class A,B,C,D or E, and within which air traffic control is not exercised; uncontrolled airspace. For specific designations and descriptions of the airspace classes, please refer to FAR Part 71.

Clean Aircraft
The principle that a pilot should not attempt a takeoff if there is frost, snow or ice adhering to:

  1. any propeller, windshield, or powerplant installation or to an airspeed, altimeter, rate of climb, or flight attitude instrument system,
  2. when snow or ice is "adhering to the wings or stabilizing or control surfaces, or
  3. when any frost is adhering to the wings or stabilizing or control surfaces, unless that frost has been polished to make it smooth.
  4. In the U.S., these are requirements spelled out in Federal Aviation Regulations (FARs). See FAR 91.527 and similar sections of FAR Parts 121, 125, and 135.

Clear Air Turbulence
Turbulence that occurs in clear air, and is commonly applied to high-level turbulence associated with wind shear.It is often encountered near the jet stream, and it is not the same as turbulence associated with cumuliform clouds or thunderstorms.

Clear ice
Generally, the formation of a layer or mass of ice which is relatively transparent because of its homogeneous structure and small number and size of air spaces; used commonly as synonymous with glaze. Factors which favor clear icing are large drop size, rapid accretion of supercooled water and slow dissipation of latent heat of fusion.

Cockpit
The compartment which houses the pilots and contains all of the controls and navigation equipment with which to fly the aircraft. Also known as the flight deck.

Cockpit Voice Recorder (CVR)
The CVR records radio transmissions and sounds in the cockpit, such as the pilot's voices, engine noises and warnings on four channels. The CVR is either a magnetic tape, which records 30 minutes of data, or solid state digital, which records two hours of data. From the sounds recorded on the CVR, parameters such as engine rpm, system failures, speed and the time at which certain events occur can often be determined. Communications with Air Traffic Control, automated radio weather briefings, and conversation between the pilots and ground or cabin crew also are recorded.

Though known as a "black box," the CVR is actually orange so that it is more visible. CVRs are typically located in the tail of the aircraft and are designed to withstand an impact of 3400 Gs, a fire of 1100° Cfor 30 minutes and 20,000 feet of water pressure. Each recorder is equipped with an underwater locator beacon (ULB) to assist in locating it in the event of an overwater accident.

Congress has required that the NTSB not release any part of a CVR tape recording, though written transcripts are made public.

Code Sharing
A marketing practice in which two airlines share the same two-letter code used to identify carriers in the computer reservation systems.

Combi aircraft
A type of aircraft whose main deck is divided into two sections, one of which is fitted with passenger seats and one of which is used for cargo.

Combined Center/RAPCON (CERAP)
An air traffic facility that combines the functions of an Air Route Traffic Control Center (ARTCC) and a radar approach control facility.

Common Traffic Advisory Frequency (CTAF)
A frequency designed for the purpose of carrying out airport advisory practices while operating to or from an airport without an operating control tower. The CTAF may be a UNICOM, Multicom, FSS or tower frequency and is identified in appropriate aeronautical publications.

Commuter
An air carrier operator operating under 14 CFR 135 that carries passengers on at least five round trips per week on at least one route between two or more points according to its published flight schedules that specify the times, day of the week and places between which these flights are performed. The aircraft that a commuter operates has 30 or fewer passenger seats and a payload capability of 7,500 pounds or less.

Compressor
A fan-like disk, or several disks, at the front end of a jet engine that draws air into the engine and compresses the air. The compressed air is then passed into a combustion chamber where it is mixed with fuel and burned, producing thermodynamic energy.

Computer Reservation System (CRS)
A system for reserving seats on commercial flights electronically. Several airlines own and market such systems, which are used by travel agents and other travel services.

Configuration
The interior layout of an airplane (e.g., number and class of passenger seats, space between rows, number of aisles, size of overhead luggage bins).

Connecting Flight
A flight requiring passengers to change aircraft and/or airlines at an intermediate stop.

Controlled Airspace
An airspace of defined dimensions within which air traffic control service is provided to IFR flights and to VFR flights in accordance with the airspace classification. Controlled airspace is a generic term that covers Class A, Class B, Class C, Class D and Class E airspace. Controlled airspace also is that airspace within which all aircraft operators are subject to certain pilot qualifications, operating rules and equipment requirements in FAR Part 91 (for specific operating requirements, please refer to FAR Part 91). For IFR operations in any class of controlled airspace, a pilot must file an IFR flight plan and receive an appropriate ATC clearance. Each Class B, Class C and Class D airspace area designated for an airport contains at least one primary airport around which the airspace is designated (for specific designations and descriptions of the airspace classes, please refer to FAR Part 71).

Controlled Flight Into Terrain (CFIT)
An accident that occurs when an otherwise functioning aircraft collides with a land mass or body of water because the pilots lost their sense of the airplane’s relation to terrain features.

Course
The intended or desired direction of flight in the horizontal plane measured in degrees from true or magnetic north.

Crosswind
Wind blowing at a right angle to the runway or the flight path of an aircraft.

Decision Height (DH)
With respect to the operation of aircraft, means the height at which a decision must be made during an instrument approach to either continue the approach or execute a missed approach.

De-icing fluid
A fluid designed to remove frozen contamination from an aircraft. See Type 1; Type 2; Type 3; Type 4

Delay
Delays are incurred when any action is taken by a controller that prevents an aircraft from proceeding normally to its destination for an interval of 15 minutes or more. This includes actions to delay departing or enroute, or arriving aircraft as well as actions taken to delay aircraft at departing airports due to conditions en route or at destination airports.

Delta
The phonetic alphabet word for the letter D.

Departures
The number of aircraft take offs actually performed in domestic and international scheduled and non-scheduled passenger/cargo and all-cargo revenue services.

Deregulation
The term commonly used in referring to the Airlines Deregulation Act of 1978 that ended government regulation of airline routes and rates.

Direct Flight
A flight with one or more intermediate stops, but no change of aircraft.

Dispatcher
An airline employee who is responsible for authorizing the departure of an aircraft. The dispatcher must ensure, among other things, that the aircraft's crew have all the proper information necessary for their flight and that the aircraft is in proper mechanical condition.

Distance Measuring Equipment (DME)
Equipment (airborne and ground) to measure, in nautical miles, the slant range distance of an aircraft from the DME navigation aid.

Domestic Operations
Operations within and between: the 50 states of the United States, the District of Columbia, the Commonwealth of Puerto Rico, the United States Virgin Islands, Canadian transborder operations, and (for certain carriers) Mexican transborder operations.

Downburst
A strong downdraft that induces an outburst of damaging winds on or near the ground. Damaging winds, either straight or curved, are highly divergent. The sizes of downbursts vary from 1/2 miles or less to more than 10 miles.

Drag
The air's resistance to moving objects.

Echo
The phonetic alphabet word for the letter E.

EFAS
See Enroute Flight Advisory Service - is a collection and dissemination point for PIREP's

Electric System
The system that uses power generated by the engines and the APU to provide electricity to the aircraft.

Elevator
A control surface on the trailing edge of the horizontal stabilizer used to control the up or down movement of the airplane's nose. In some airplanes, the entire horizontal stabilizer can move, acting as the elevator. Movement of the elevator is controlled by either the control yoke or sidestick. A trim system minimizes the force needed to hold the elevator in the proper position for climb, cruise, descent, and other flight conditions.

Empennage
The entire tail section of the aircraft containing all the various tail surfaces, including the vertical and horizontal stabilizers, elevator and rudder.

En Route Air Traffic Control Services
Air traffic control services provided to aircraft on IFR flight plans, generally by centers, when these aircraft are operating between departure and destination terminal areas. When equipment, capabilities and controller workload permit, certain advisory/assistance services may be provided to VFR aircraft.

En Route Center
see Air Route Traffic Control Center (ARTCC)

Engines
Produce thrust to propel the aircraft forward. Also provide power to the aircraft through accessories, such as engine-driven generators and hydraulic pumps.

Enplanements
The number of passengers boarding a flight.

Enroute Flight Advisory Service (EFAS)
a service by which air traffic controllers collect and disseminate pilot reports (PIREPs) on adverse airborne conditions.

Essential Air Service
Government subsidized airline service to rural areas of the United States enacted along with the Airline Deregulation Act of 1978.

Extended-Range Twin-Engine Operations (ETOPS)
Refers to the portion of a flight by a twin-engine airplane usually over an ocean that is more than one hour from an airport. ETOPS certification means that a twin-engine airplane model has reliably demonstrated the ability to fly safely from one to three hours from the nearest airport even if one engine fails.

Fatigue
Weakness in aircraft structural material resulting from prolonged stress.

Federal Aviation Administration (FAA)
The government agency responsible for air safety and operation of the air traffic control system. The FAA also administers a program that provides grants from the Airport and Airway Trust Fund for airport development.

Federal Aviation Regulation (FAR)
14 Code of Federal Regulations.

Ferry Flight
A flight for the purpose of: returning an aircraft to base, delivering an aircraft from one location to another, or moving an aircraft to and from a maintenance base. Ferry flights, under certain conditions, may be conducted under terms of a special flight permit. They do not carry revenue passengers.

First Officer
Assists and relieves the captain; requires a commercial pilot certificate or license with instrument rating.

Flaps
Control surfaces on the trailing edge of the wing which are used to increase the amount of lift generated by the wings at slower speeds. Allow aircraft to takeoff and land at slower speeds.

Flight Data Recorder (FDR)
FDRs record many different operating conditions of the flight. By regulation, newly manufactured aircraft must monitor at least 28 important parameters such as time, altitude, airspeed, heading and aircraft attitude. In addition, some FDRs can record the status of more than 300 other in-flight characteristics that can aid in an incident or accident investigation. The items monitored can be anything from flap position to auto-pilot mode or even smoke alarms. FDRs are either a magnetic tape or solid state digital and record 25 hours of data.

Though known as a "black box," the FDR is actually orange so that it is more visible. FDRs, which are typically located in the tail of the aircraft, are designed to withstand an impact of 3,400 Gs, a fire of 1,100° C for 30 minutes and 20,000 feet of water pressure. Each recorder is equipped with an Underwater Locator Beacon (ULB) to assist in locating it in the event of an overwater accident.

Flight Deck
The compartment which houses the pilots and contains all of the controls and navigation equipment with which to fly the aircraft. Also known as the cockpit.

Flight Level (FL)
A level of constant atmospheric pressure related to a reference datum of 29.92 inches of mercury. Each is stated in three digits that represent hundreds of feet. For example, flight level 250 represents a barometric altimeter indication of 25,000 feet; flight level 255, an indication of 25,500 feet.

Flight Operations Quality Assurance (FOQA)
FOQA programs would give the FAA access to in-flight recorded data collected by airlines to improve safety in the following areas: flight crew performance; training; air traffic procedures; airport maintenance and design; and aircraft operations and design. Airline participation is voluntary. The FAA, labor and industry are working with NASA Ames on research and development. A model program has been initiated with some major airlines.

Flight Plan
A planning document that covers the expected operational details of a flight such as destination, route and fuel on board. It is filed with an FSS or an ATC facility either orally or in writing. There are both VFR and IFR flight plans. VFR plans are not mandatory.

Flight Service Station (FSS)
Air traffic facilities that provide pilot briefing, enroute communications and VFR search and rescue services; assist lost aircraft and aircraft in emergency situations; relay ATC clearances; originate NOTAMS; broadcast aviation weather and NAS information; receive and process IFR flight plans; and monitor NAVAIDs. In addition, at selected locations, FSSs provide En route Flight Advisory Service (Flight Watch), take weather observations, issue airport advisories and advise Customs and Immigration of transborder flights.

Flight Simulator
A ground-based device, used to train pilots, that simulates flight scenarios, including emergency situations.

Fly-by-Wire (FBW)
A term frequently used for electronic or digital flight controls.

Flying Pilot (FP)
The pilot at the controls of the aircraft.

Foxtrot
The phonetic alphabet word for the letter F.

Freedom Of Information Act (FOIA)
Allows all U.S. citizens and residents to request any records in possession of the executive branch of the federal government. The term "records" includes documents, papers, reports, letters, films, photographs, sound recordings, computer tapes and disks. An object that cannot be reproduced is not considered a record in this case. The FOIA covers the President's cabinet agencies, independent agencies, regulatory commissions and government-owned corporations. Congress is exempt, as are the federal court and state and local governments. Some states and municipalities have laws modeled after the FOIA. The federal act includes nine exemptions that agencies may claim as a basis for withholding information. An administrative appeal can be filed that argues for disclosure based on benefits to the public vs. privacy. If a good argument is made, appellate reviewers may waive an exemption.

Freight
All air cargo excluding mail.

Freight-Ton Mile
A ton of freight moved one mile. It is the standard measure of air freight activity.

Frequent-Flyer Programs
Airline marketing programs designed to win customer loyalty by giving them "points" for each mile flown. Points can be redeemed later for free flights or upgrades in cabin service.

Frost
Ice crystal deposits formed by sublimation when temperature and dew point are below freezing.

Fuel System
A series of compartments in the wings from which fuel is supplied to the engines. Some aircraft have additional fuel storage in the empennage.

Fuselage
The central body portion of an aircraft. Houses the crew, passengers and cargo and is pressurized and temperature controlled. An aircraft's wing and tail are not considered part of the fuselage.

General Aviation
All aviation that is not commercial or military.

Glass Cockpit
A term used to refer to the cockpits of modern airliners containing state-of-the-art flat panel, liquid crystal displays.

Glaze
A coating of ice, generally clear and smooth, formed by freezing of supercooled water on a surface.

Glideslope
The ideal descent path to a runway. It can be electronically defined by radio signals transmitted from the ground such as during an ILS approach. An aircraft carrying a special ILS radio receiver can detect this electronic glidepath and follow it down to the runway.

Global Analysis Information Network (GAIN)
GAIN is designed to help the aviation industry prevent accidents by making safety information available to aviation professionals worldwide who can use it to improve safety. By learning more about potential problems, the GAIN participants can use the information to address problems proactively. Actions could include pilot training, procedural changes to manuals, modifications to air traffic control procedures, changes to maintenance or manufacturing procedures, and design changes. The privately owned and operated international system will draw from various worldwide aviation information sources.

Global Positioning System (GPS)
A constellation of orbiting satellites that enables flight crews and ground-based controllers to continuously chart an aircraft's exact position in longitude, latitude and altitude. GPS allows air-traffic controllers to monitor aircraft locations anywhere in the world without the use of ground-based radar. GPS technology also enables pilots to select more direct flight paths, find runways and make pinpoint, computer-assisted landings regardless of visibility.

Golf
The phonetic alphabet word for the letter G.

Ground Proximity Warning System (GPWS)
A multiple warning system integrated with aircraft altimeters and activated within 2,500 feet of the ground that alerts a flight crew of an excessive descent, flight into rapidly rising terrain or unusually low descent on the approach to a landing.

Groundspeed
Speed of the aircraft in relation to the ground.

Gust
A sudden brief increase in wind. According to the U.S. weather-observing practice, gusts are reported when the variation in wind speed between peaks and lulls is at least 10 knots.

Gyroplane
A rotorcraft whose rotors are not engine-driven, except for initial starting, but are made to rotate by action of the air when the rotorcraft is moving; and whose means of propulsion, consisting usually of conventional propellers, is independent of the rotor system.

Heading
The direction in which the longitudinal axis of the airplane points with respect to true or magnetic north. Heading is equal to course plus or minus any wind correction angle.

Helicopter
A rotorcraft that, for its horizontal motion, depends principally on its engine-driven rotors.

Holdover time
the estimated time that de-icing or anti-icing fluid will prevent the formation of frost or ice and the accumulation of snow on an aircraft to which it has been applied. The time starts when the final application of fluid starts and expires when the fluid loses its effectiveness. Pilots are provided with Holdover Timetables. These help them determine whether they can take off before the fluid loses its effectiveness. Holdover times are only guidelines because many variables can reduce the effectiveness of de-icing and anti-icing fluids, including the precipitation rate, wind speed, aircraft skin temperature and jet blast from other aircraft.

Horizontal Stabilizer
The airfoil or small wing at the rear of the aircraft that balances lift forces generated by the wings and increases stability. In some airplanes, the stabilizer is fixed and the elevator attached to its trailing edge. In other airplanes, the entire stabilizer can move, acting as the elevator, which controls the up or down movement of the airplane's nose. A trim system minimizes the force needed to hold the elevator in the proper position for climb, cruise, descent, and other flight conditions.

Hotel
The phonetic alphabet word for the letter H.

Hours Flown
The airborne hours in domestic and international scheduled and non-scheduled revenue service, computed from the moment an aircraft leaves the ground until it touches the ground again.

Hub and Spoke
A system for deploying aircraft that enables a carrier to increase service options at all airports encompassed by the system. It entails the use of a strategically located airport (the hub) as a passenger exchange point for flights to and from outlying towns and cities (the spokes).

Hypersonic Flight
Flight conducted at speeds greater than Mach 5, or five times the speed of sound.

Hypoxia
The effects on the human body of an insufficient supply of oxygen.

Ice Crystal Clouds
Clouds that exist at very cold temperatures at which their moisture has frozen to the solid or crystal state.

Ice Fog
A type of fog composed of minute suspended particles of ice; occurs at very low temperatures and may cause a halo phenomenon.

Icing
The accumulation of frozen precipitation on an aircraft's wings, control surfaces, engine inlets or propellers and other components. The build-up of even small amounts of ice can reduce an aircraft's lift, making it difficult or impossible to maintain control. There are generally three types of ice:

  1. Rime - Rough, milky, opaque ice formed by instantaneous freezing of small supercooled water droplets.
  2. Clear - glossy, clear or translucent ice formed by the relatively slow freezing of large supercooled water droplets.
  3. Mixed - Mixture of rime and clear ice.
  4. In addition, icing is currently classified into four severity categories:
  1. Trace - Ice becomes perceptible. Rate of accumulation slightly greater than rate of sublimation. It is not hazardous even though deicing/anti-icing equipment is not utilized, unless encountered for an extended period of time - over one hour.
  2. The rate of accumulation may create a problem if flight is prolonged in this environment (over one hour). Occasional use of deicing/anti-icing equipment removes/prevents accumulation. It does not present a problem if the deicing/anti-icing equipment is used.
  3. The rate of accumulation is such that even short encounters become potentially hazardous and use of deicing/anti-icing equipment or diversion is necessary.
  4. The rate of accumulation is such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary.
(SOURCE: National Center for Atmospheric Research, Second Aviation Weather Workshop, Nov. 17, 1993)

IFR Aircraft/IFR Flight
An aircraft conducting flight in accordance with instrument flight rules.

Incident
An occurrence other than an accident associated with the operation of an aircraft that affects or could affect the safety of operations.

India
The phonetic alphabet word for the letter I.

Indicated Airspeed (IAS)
The speed of an aircraft as shown on the airspeed indicator.

Instrument Flight Rules (IFR)
A set of rules governing the conduct of flight under instrument meteorological conditions. Under IFR, an aircraft is required to be in contact with air traffic control facilities and is separated by ATC from all other IFR aircraft.

Instrument Landing System (ILS)
An aircraft landing system that provides radio-based horizontal and vertical guidance to an aircraft approaching a runway. It is used to guide landing aircraft during conditions of low visibility.

Instrument Meteorological Conditions (IMC)
Meteorological conditions expressed in terms of visibility, distance from clouds and ceiling less than minima specified for visual meteorological conditions.

Instrument Operations
Arrivals or departures of an aircraft in accordance with an IFR flight plan or special VFR procedures, or an operation where IFR separation between aircraft is provided by a terminal control facility. There are three kinds of instrument operations:

  • Primary Instrument Operations arrivals and departures at the primary airport that is normally the airport at which the approach control facility is located.
  • Secondary Instrument Operations arrivals and departures at airports other than the primary airport.
  • Overflights operations in which an aircraft transits the area without intent to land.

Jet Stream
A narrow band of winds with speeds of 50 knots and greater embedded in the westerlies in the high troposphere.

Jetway
A registered trademark for a certain kind of aircraft loading bridge that allows passengers direct, protected access to an aircraft from the terminal.

Juliett
The phonetic alphabet word for the letter J.

Kilo
The phonetic alphabet word for the letter K.

Knot
An abbreviation for one nautical mile per hour. In terms of distance, a knot is 15 percent longer than a statute mile. Therefore, a knot is equal to 1.15 statute miles or 1.85 kilometers.

Landing Gear
Those components comprising the tires, wheels and related assembly upon which an aircraft lands, and which provides mobility for the aircraft while on the ground. Includes all supporting components, such as the tail wheel or tail skid. Retracted during flight.

Latitude
Measurement north or south of the equator in degrees, minutes and seconds.

Lift
The force generated by the movement of air across the wings of an aircraft. When enough lift is generated to overcome the weight of an aircraft, the aircraft rises.

Lima
The phonetic alphabet word for the letter L.

Load Factor
The percentage of available seats that are filled with paying passengers. Technically, load factor is equal to revenue passenger miles divided by available seat miles.

Localizer
Part of an ILS that provides lateral or horizontal course guidance throughout the descent path to the runway threshold.

Long Range Navigation (LORAN)
An electronic navigational system by which lines of position are determined by measuring the difference in the time of reception of synchronized pulse signals from fixed transmitters. LORAN-C operates in the 100-110 kHz frequency band.

Longitude
Measurement east or west of the prime meridian in degrees, minutes and seconds.

Loss of control
An unintentional upset defined by one or more of the following: pitch attitude more that 25 degrees nose up; pitch attitude more than 10 degrees nose down; bank angle greater than 45 degrees; flight within those parameters at airspeeds inappropriate for the conditions.

Lower hold
The bottom section of a plane's fuselage, used for stowing cargo.

Magnetic Course
True course corrected for magnetic variation.

Major Carrier
An airline with annual revenue of more than $1 billion.

Maneuvering Speed (Va)
The maximum speed at which full and abrupt control movements will not overstress the airplane.

Mean Sea Level (MSL)
The average height of the surface of the sea for all stages of tide that is used as a reference for elevations throughout the United States.

Medical Certificates

Microburst
A small downburst with outbursts of damaging winds extending 2.5 miles or less. In spite of its small horizontal scale, an intense microburst can induce wind speeds as high as 150 knots.

Mike
The phonetic alphabet word for the letter M.

Miles Flown
The miles (computed in airport-to-airport distances) for each inter-airport leg actually completed in domestic and international revenue services, scheduled and non-scheduled. In cases where the inter-airport distances are not applicable, aircraft miles flown are determined by multiplying the normal cruising speed for the aircraft type by the airborne hours.

Military Operations Area (MOA)
Special use airspace of defined vertical and lateral limits established to help VFR traffic identify locations where military activities are conducted.

Military Training Route (MTR)
Route depicted on an aeronautical chart for the conduct of military flight training at speeds above 250 knots.

Minimum Equipment List (MEL)
A list of aircraft equipment that must be in good working order before an aircraft may legally take off with passengers. Repairs to some items not essential to an aircraft's airworthiness may be deferred for limited periods of time as approved by the FAA.

Minimum Safe Altitude Warning System (MSAW)
Designed to alert ATC when an aircraft is in unsafe proximity to terrain or obstructions.

Movement Area
Runways, taxiways and other areas of an airport used by aircraft for taxi, takeoff and landing, excluding ramps and parking areas.

Nacelle
Cone shaped covering, which houses the engines.

National Airspace System (NAS)
The common network of U.S. airspace; air navigation facilities, equipment and services, airports or landing areas; aeronautical charts, information and services; rules, regulations and procedures; technical information; and human resources and material. Included are system components shared jointly with the military.

National Aviation Safety Data Analysis Center (NASDAC)
The NASDAC is an automated support capability that enables users to apply powerful state-of-the-art analysis tools to an integrated database containing safety data from multiple sources. The NASDAC database currently includes data from over 20 source systems. A walk-in NASDAC facility is open in the FAA Headquarters building.

National Carrier
An airline with annual revenues of between $100 million and $1 billion.

Nautical Mile
Equal to 1.15 statute miles or 1.85 kilometers.

Navigational Aid (NAVAID)
Any visual or electronic device airborne or on the surface which provides point-to-point guidance information or position data to aircraft in flight.

Near Midair Collision (NMAC)
A situation where aircraft fly within 500 feet of one another, or any time a member of a flightcrew reports that two aircraft were in danger of colliding. The degrees of hazard are:

  • Critical A situation in which collision avoidance was due to chance rather than an act on the part of the pilot. Less than 100 feet of aircraft separation would be considered critical.
  • Potential An incident which would probably have resulted in a collision if no action had been taken by either pilot. Closest proximity of less than 500 feet would usually be required in this case.
  • No hazard A situation in which direction and altitude would have made a midair collision improbable regardless of evasive action taken.

Nondirectional Beacon (NDB)
A low/medium frequency (L/MF) or UHF radio beacon transmitting nondirectional signals whereby the pilot of an aircraft equipped with direction finding equipment can determine his bearing to or from the radio beacon and "home" on or track to or from the station. When the radio beacon is installed in conjunction with the Instrument Landing System marker, it is normally called a Compass Locator.

Non-Scheduled Service
Revenue flights, such as charter flights, that are not operated in regular scheduled service and all nonrevenue flights.

Nonstop Flight
A flight with no intermediate stops.

Notice of Proposed Rulemaking (NPRM)
A public notice issued by th FAA preliminary to rulemaking, and is most cases establishing a period for public comment.

Notice to Airmen (NOTAMS)
A notice containing a recent change to any component in the National Airspace System that is considered essential to persons concerned with flight operations.

November
The phonetic alphabet word for the letter N.

Operational Deviation (OD)
An occurrence where applicable separation minima, as referenced in the operational error definition below were maintained, but: (1) less than the applicable separation minima existed between an aircraft and protected airspace without prior approval, (2) an aircraft penetrated airspace that was delegated to another position of operation or another facility without prior coordination and approval, (3) an aircraft penetrated airspace that was delegated to another position of operation of another facility at an altitude or route contrary to the altitude or route requested and approved in direct coordination or as specified in a Letter of Agreement, pre-coordination or internal procedure, (4) an aircraft, vehicle, equipment or personnel encroached upon a landing area that was delegated to another position of operation without prior coordination and approval.

Operational Error (OE)
An occurrence attributable to an element of the air traffic control system that results in less than the applicable separation minima between two or more aircraft, or between an aircraft and terrain or obstacles.

Oscar
The phonetic alphabet word for the letter O.

Papa
The phonetic alphabet word for the letter P.

Part 121 of the Federal Aviation Regulations
The FAA safety regulations covering operators of scheduled passenger-carrying operations in airplanes that have passenger-seating configurations of 10 or more seats (excluding any crewmember seat) and those conducting scheduled passenger-carrying operations in turbojet airplanes regardless of seating configuration.

Part 135 of the Federal Aviation Regulations
The FAA safety regulations covering operators of aircraft having fewer than 10 seats generally commuter and on-demand aircraft.

Passenger Facility Charge (PFC)
A tax authorized by Congress, approved by the Federal Aviation Administration, assessed by airports and collected by airlines as an add-on to the fare. It is designed to help pay for airport improvements that enhance safety and capacity.

Payload
The total passenger and cargo weight an aircraft is carrying or is capable of carrying.

Phonetic Alphabet
Adopted by ICAO to avoid misunderstanding of letters which sound alike, especially during radio communication. Phonetic alphabet chart.

Phonetic Alphabet Card
PHONETIC ALPHABET
LETTER WORD SPOKEN AS
A ALPHA AL FAH
B BRAVO BRAH VOH
C CHARLIE CHAR LEE
SHAR LEE
D DELTA DELL TAH
E ECHO ECK OH
F FOXTROT FOKS TROT
G GOLF GOLF
H HOTEL HOH TELL
I INDIA IN DEE AH
J JULIETT JEW LEE ETT
K KILO KEY LOH
L LIMA LEE MAH
M MIKE MIKE
LETTER WORD SPOKEN AS
N NOVEMBER NO VEM BER
O OSCAR OSS CAH
P PAPA PAH PAH
Q QUEBEC KEH BECK
R ROMEO ROW ME OH
S SIERRA SEE AIR RAH
T TANGO TANG GO
U UNIFORM YOU NEE FORM/
OO NEE FORM
V VICTOR VIK TAH
W WHISKEY WISS KEY
X XRAY ECKS RAY
Y YANKEE YANG KEY
Z ZULU ZOO LOO

Pilot Deviation (PD)
The actions of a pilot which result in the violation of a Federal Aviation Regulation (FAR) or a North American Aerospace Defense Command (NORAD) Air Defense Identification Zone (ADIZ) tolerance.

Pilot in Command (PIC)
The pilot responsible for the operation and safety of an aircraft during flight time.

Pilot Report
See PIREP

PIREP
A report by a pilot to air traffic controllers, and through the controllers to other pilots, on airborne conditions, particularly adverse ones. FAA air traffic control facilities solicit PIREPs when bad weather conditions are reported or forecast. The reports are voluntary, but their information is extremely helpful to other pilots planning flights. A PIREP should include the type and identification number of the aircraft from which the report is made; the location, time and altitude at which the conditions were observed; weather conditons, and other pertinent remarks.

Pitch
A description of the movement of the nose of an aircraft up or down in relation to its previous attitude.

Positive Control
The separation of all air traffic within designated airspace by air traffic control.

Pressurized Aircraft
An aircraft that is kept at a designated atmospheric pressure to enable passengers and crew to breath normally.

Propfan
One of several terms used to describe new generations of jet engines that typically turn very large, multi-bladed propeller-like fans in order to produce the thrust needed for flight.

Prop-jet
Aircraft that use turbine engines to drive external propellers (see turboprop).

Pylon
An aircraft part that connects an engine to either a wing or the fuselage.

Quebec
The phonetic alphabet word for the letter Q.

Radar
Term coined from the phrase "Radio Detecting and Ranging." It is based on the principle that ultra-high frequency radio waves travel at a precise speed and are reflected from objects they strike. It is used to determine an object's direction and distance.

Ramp
The aircraft parking area at an airport, usually adjacent to a terminal.

Range
The maximum distance, based on fuel capacity and rate of fuel consumption, that an aircraft is capable of transporting passengers and/or freight.

Rating
A statement that, as part of a certification, sets forth special conditions, privileges or limitations.

Regional Carrier
An airline with annual revenues of less than $100 million whose service generally is focused on a particular geographic region.

Revenue
Money paid for carriage of passengers or cargo.

Revenue Passenger Mile (RPM)
One paying passenger flown one mile. It is the principal measure of airline passenger traffic.

Rime Ice
The formation of a white or milky and opaque granular deposit of ice formed by the rapid freezing of supercooled water droplets as they impinge on an exposed aircraft.

Roll
A description of the rolling or banking movement of an aircraft to the left or right. The wing ailerons control roll.

Romeo
The phonetic alphabet word for the letter R.

Rotorcraft
An aircraft that depends principally on the lift generated by one or more rotors to support its flight. Includes helicopters and gyroplanes.

Rudder
A control surface on the trailing edge of the vertical stabilizer that controls the yaw motion of the aircraft - that is, the motion of the nose of the aircraft left or right. A trim system minimizes the force needed to hold the rudder in the proper position for various flight conditions.

Runway Incursion
Any airport occurrence that involves an aircraft, ground vehicle, person or object on the ground, and that creates a collision hazard or results in loss of separation with an aircraft taking off, intending to takeoff, landing or intending to land.

Safety Performance Analysis System (SPAS)
SPAS is a computer-based system designed to help inspectors identify potential safety risks by tracking the performance of operators, aircraft and personnel.

Scheduled Air Carrier
An air carrier that operates scheduled service.

Scheduled Service
Transport service operated pursuant to published flight schedules, including extra sections and related nonrevenue flights.

Seat Pitch
The distance between seats in an aircraft's passenger cabin as measured from any point on a given seat to the corresponding point on the seat in front of or behind it for example, from the front edge of a seat cushion to the front edge of another seat cushion in the next row.

Second Officer
A pilot who assists in flight operations and ensures that the mechanical and electronic devices are operational; requires a flight engineer’s certificate from the FAA.

Separation Minima
The minimum longitudinal, lateral or vertical distances by which aircraft are spaced through the application of air traffic control procedures.

Service Bulletin
An advisory from an airplane manufacturer to airlines and government regulators regarding recommended aircraft inspections, maintenance or modifications.

Sierra
The phonetic alphabet word for the letter S.

Slats
Moveable surfaces on the leading edge of the wing. During takeoff and landing, they are extended to produce extra lift.

SLW
See supercooled liquid water

Special Use Airspace (SUA)
Airspace of defined dimensions identified by an area on the surface of the earth wherein activities must be confined because of their nature and/or wherein limitations may be imposed upon aircraft operations that are not a part of those activities. Types of special use airspace are:

  • Alert Area Airspace which may contain a high volume of pilot training activities or an unusual type of aerial activity, neither of which is hazardous to aircraft. Alert Areas are depicted on aeronautical charts for the information of nonparticipating pilots. All activities within an Alert Area are conducted in accordance with Federal Aviation Regulations. Pilots of participating aircraft as well as pilots transiting the area are equally responsible for collision avoidance.
  • Controlled Firing Area Airspace wherein activities are conducted under conditions so controlled as to eliminate hazards to nonparticipating aircraft and to ensure the safety of persons and property on the ground.
  • Military Operations Area (MOA) Airspace established outside of Class A airspace area to separate or segregate certain nonhazardous military activities from IFR traffic and to identify for VFR traffic where these activities are conducted. (Refer to Airman's Information Manual)
  • Prohibited Area Airspace designated under FAR Part 73 within which no person may operate an aircraft without the permission of the using agency. (Refer to En route Charts, AIM)
  • Restricted Area Airspace designated under FAR Part 73, within which the flight of aircraft, while not wholly prohibited, is subject to restriction. Most restricted areas are designated joint use and IFR/VFR operations in the area may be authorized by the controlling ATC facility when that airspace is not being utilized by the using agency. Restricted areas are depicted on en route charts. Where joint use is authorized, the name of the ATC controlling facility is also shown. (Refer to FAR Part 73 and AIM)
  • Warning Area Airspace of defined dimensions extending from three nautical miles outward from the coast of the United States that contains activity potentially hazardous to nonparticipating aircraft. The purpose of such warning area is to warn nonparticipating pilots of the potential danger. A warning area may be located over domestic or international waters, or both.

Speed Brakes
Also known as air brakes, they are surfaces that are normally flush with the wing or fuselage in which they are mounted, but which can be extended into the airflow to create more drag and slow the aircraft.

Spin
AA maneuver, intentional or unintentional, in which an airplane after stalling descends nearly vertically, nose low, with its tail revolving around the near vertical axis of descent.

Spoilers
Panels on the upper surface of the wing that, when raised, "spoil" the airflow across the wing, both increasing drag and decreasing lift. Outboard spoilers are used during flight to slow the aircraft and expedite descent. Both inboard and outboard spoilers are used during landing to aid in slowing the aircraft upon touchdown.

Stage 2
Term used to describe jets that meet certain noise parameters on takeoff and landing.

Stage 3
Term used to describe the quietest jets in service. All new jets being manufactured are "stage 3."

Stall
An aerodynamic condition, this type of stall has nothing to do with a failure of the airplane's engines. An aerodynamic stall occurs when a wing exceeds its critical angle of attack and suddenly loses the ability to generate enough lift to keep the airplane flying. At the same time, drag on the wing suddenly increases. Typically, when an airplane enters a stall, its nose will drop, decreasing the angle of attack and increasing the airspeed to aid in recovering from the stall. Aircraft are designed so that a stall is preceded by a vibration, or buffet, that alerts the pilot to the impending loss of lift. Many aircraft are fitted with other devices, such as stall-warning horns and "stick shakers" that also alert the pilot. In addition, airplanes are designed so that if a stall is encountered, both wings will stall at once, which helps keep the wings level and avoid a spin.

Stall Speed
The speed at which air flow separates from a wing, causing a sudden drop in lift and a sudden increase in drag. The stall speed varies with: a) the wing's angle of attack; b) with different types of aircraft; c) with the position of flaps, slats, landing gear and other devices on an aircraft, and d) with the degree and rate of the turn that an aircraft may be making. In normal use, the term means the slowest speed at which an aircraft can maintain straight and level flight. However, an aircraft can stall at virtually any speed if an acceptable angle of attack is exceeded.

Stick Shaker
A warning device in the cockpit which alerts pilots that their aircraft is approaching a stall-producing angle of attack. The device creates a shaking action in the pilot's control stick or control column.

Supercooled Clouds
Clouds containing water droplets that have remained in the liquid state even though the ambient temperature may be below freezing. The droplets typically are very small (five to 100 microns--one micron [or micrometer] is one millionth of one meter or .00003937 inches. By comparison, rain droplets range from 500 to 2,000 microns, and freezing drizzle droplets are less than 500 microns in size.) These droplets freeze on impact with another object. Water droplets have been observed to remain liquid even at temperatures as low as minus 40 deg. Fahrenheit.

Supercooled Liquid Water
Water that remains liquid even though its temperature is below freezing. When a cold aircraft strikes a supercooled liquid water droplet, part of the droplet freezes instantly, adhering to the aircraft's skin. Friction warms the remaining portion of the supercooled water, but aerodynamic cooling can cause it to refreeze.

Supersonic Flight
Flight at speeds greater than the speed of sound, that varies according to altitude, but is more than 700 miles per hour at sea level.

Tailwind
Any wind more than 90 degrees from the heading of the runway.

Tango
The phonetic alphabet word for the letter T.

Terrain Alert Warning System (TAWS)
A device installed in aircraft that provides pilots with a detailed, moving map of nearby terrain to help them maintain proper altitude and terrain clearance. An audio alert automatically sounds in the cockpit if an airplane approaches threatening proximity to terrain. (See Enhanced Ground Proximity Warning System).

Threshold
The beginning of the landing area of the runway.

Thrust
The force produced by a jet engine or propeller. It can also be defined as the forward reaction to the rearward movement of a jet exhaust.

Thrust Reverser
Provides a method of reversing the thrust of the engine to assist in slowing the aircraft upon landing. There are several methods of obtaining reverse thrust on turbo-jet engines, including blocker doors which move into the air flow to redirect it, and clam shells, which extend into the exhaust from behind the engine.

Track
The actual flight path of an aircraft over the ground.

Traffic Advisories
Advisories issued to alert pilots of other known or observed air traffic which may be in such proximity to their position or intended route of flight as to warrant their attention.

Traffic Alert and Collision Avoidance System (TCAS)
An electronic system installed in aircraft that searchs for and alerts pilots to the presence of other aircraft. More advanced versions of TCAS also advise pilots of actions to take to avoid approaching aircraft, if warranted.

Traffic Pattern
The traffic flow that is prescribed for aircraft landing and taking off from an airport.

Transponder
An electronic device that "responds" to interrogation by ground-based radar with a special four-digit code that specifically identifies the aircraft on which it is located. Certain transponders have the ability to transmit automatically the altitude of the aircraft in addition to the special code.

Trim System
The position of the flight control surfaces needed to maintain an airplane in a constant attitude changes depending on the flight condition - climb, cruise, descent, banking, landing, etc. Trim systems minimize, or "trim out" the forces needed to hold the flight controls in the proper position for these various conditions of flight. The ailerons, elevators (or, in some aircraft, horizontal stabilizers), rudders, or other flight control surfaces of most airplanes each have a trim system.

True Airspeed (TAS)
The speed at which an aircraft is moving through the surrounding air.

True Altitude
The actual height of an object above mean sea level.

True Course (TC)
The intended or desired direction of flight as measured on a chart clockwise from true north.

True Heading
The direction the longitudinal axis of the airplane points with respect to true north. True heading is equal to true course plus or minus any wind correction angle.

Turbofan
A type of jet engine in which a certain portion of the engine's airflow bypasses the combustion chamber, passing instead through a fan that surrounds the combustion chamber.

Turbojet
The original designation for a "pure" jet engine whose power is solely the result of its jet exhaust.

Turboprop
A type of engine that uses a jet engine to turn a propeller. Turboprops are often used on regional and business aircraft because of their relative efficiency at speeds slower than, and altitudes lower than, those of a typical jet.

Type 1
A fluid made to SAE or ISO standards so that it contains a minimum of 80% glycol. The fluid has a low viscosity and is considered "unthickened." It used heated and diluted for de-icing aircraft.

Type 2
A fluid made to SAE or ISO standards so that it contains a minimum of 50% glycol. It has a thickening agent added to increase its viscosity and enable the fluid to be deposited in a thicker film that remains on the aircraft's surfaces until takeoff. Handled and applied properly, Type 2 should remain on an aircraft's wings during ground operations or short-term storage to provide anti-icing protection, then will be shed off the surfaces during takeoff roll without adverse effect on aerodynamic performance. Type 2 fluids are designed to be used only on aircraft with a takeoff rotation speed greater than 85 knots.

Type 3
A fluid made to SAE or ISO standards for anti-icing protection of aircraft with takeoff rotation speed greater than 60 knots. The glycol-based fluid contains a thickening agent that increases its viscosity and enables it be deposited in a film that remains on the aircraft's surfaces until takeoff rotation speed is reached. Handled and applied properly, Type 3 should remain on an aircraft's wings during ground operations or short-term storage to provide anti-icing protection, then will be shed off the surfaces during takeoff roll without adverse effect on aerodynamic performance.

Type 4
A fluid made to SAE or ISO standards so that it contains a minimum of 50% glycol. It has a thickening agent added to increase its viscosity and enable the fluid to be deposited in a thicker film that remains on the aircraft's surfaces until takeoff. Handled and applied properly, Type 4 will remain on an aircraft's wings during ground operations or short-term storage to provide anti-icing protection, then will be shed off the surfaces during takeoff roll without adverse effect on aerodynamic performance. Type 2 fluids are designed to be used only on aircraft with a rotation speed greater than 100 knots.

Ultralight Vehicle
An aeronautical vehicle operated for sport or recreational purposes which does not require FAA registration, an airworthiness certificate or pilot certification. They are primarily single occupant vehicles, although some two-person vehicles are authorized for training purposes. Operation of an ultralight vehicle in certain airspace requires authorization from ATC.

Uncontrolled Airspace
Known as Class G Airspace. Consists of the airspace not designated controlled airspace (Class A, B, C, D and E).

Unducted Fan
A kind of engine that uses the basic core of a jet engine to drive large, fan-like blades that produce the major thrust component of the engine. A propfan is one kind of unducted fan.

Uniform
The phonetic alphabet word for the letter U.

Unscheduled Air Carrier
An air carrier operating in an on-demand capacity, without a set time schedule.

Vehicle/Pedestrian Deviation (VPD)
An entry or movement on an airport movement area by a vehicle operator or pedestrian that has not been authorized by air traffic control (includes aircraft operated by a non-pilot).

Vertical Stabilizer
The large "tail" surface on the top rear of the fuselage used to increase stability. The rudder is attached to the trailing edge of the vertical stabilizer and controls the left or right movement of the airplane's nose. A trim system minimizes the force needed to hold the rudder in the proper position for various flight conditions.

Very High Frequency Omnidirectional Range (VOR)
A ground-based electronic navigation aid transmitting very high frequency navigation signals, 360-degrees in azimuth, oriented from magnetic north. VOR is used as the basis for navigation in the National Airspace System. The VOR periodically identifies itself by Morse Code and may have an additional voice identification feature. Voice features may be used by ATC or FSS for transmitting instructions/information to pilots.

Victor
The phonetic alphabet word for the letter V.

Visual Flight Rules (VFR)
Rules that govern the procedures for conducting flight under visual meteorological conditions (VMC). Aircraft flying under VFR are not required to be in contact with air traffic controllers and are responsible for their own separation from other aircraft. The term also is used in the United States to indicate weather conditions that are equal to or greater than minimum VFR requirements. In addition, it is used by pilots and controllers to indicate a type of flight plan.

Visual Meteorological Conditions (VMC)
Meteorological conditions expressed in terms of visibility, distance from clouds and ceiling equal to or better than specified minima.

VORTAC
A navigational system that provides both VOR and TACAN course guidance, plus distance (DME) information.

Vortices
See wingtip vortices

Warning Area
Special use airspace that may contain hazards to nonparticipating aircraft over international and coastal waters.

Weight
The gravitational force pulling downward on an aircraft; the opposite of lift.

Whiskey
The phonetic alphabet word for the letter W.

Wide-body Aircraft
Generally considered to be any airliner with more than one aisle in the passenger cabin. Examples of widebody aircraft include the Boeing 747, 767 and 777; the Lockheed L-1011; the McDonnell Douglas DC-10; and Airbus Industrie's A300 and A310. Technically, any aircraft with a fuselage diameter in excess of 200 inches may be considered a wide-body.

Windshear
Weather phenomenon entailing a strong downdraft of air that can result in the loss of lift for an aircraft passing through it.

Wing
A general term applied to the airfoil, or one of the airfoils, designed to develop a major part of the lift of an aircraft. Air pressure over and under the wings creates lift.

Wingtip Vortices
Circular patterns of air created by an airfoil when generating lift. Vortices from medium to heavy aircraft may be extremely hazardous to small aircraft trailing too close.

X-ray
The phonetic alphabet word for the letter X.

Yankee
The phonetic alphabet word for the letter Y.

Yaw
A description of the movement of the nose of an aircraft from side to side, or left and right. Yaw motion is controlled by the vertical stabilizer and the rudder.

Yield
A measure of airline revenue derived by dividing passenger revenue by passenger miles. It is expressed in cents per mile.

Yield Management
The term used to describe the process airlines use to set prices for a flight. The goal is to find the mix of seat prices that produces the most revenue for any given flight.

Zulu
(1) The phonetic alphabet word for the letT) (also Universal Time Coordinate), used to log events (such as pushback, tater Z. (2) The designator for Greenwich Mean Time (GMkeoff, landing) in an aviation operation.

 




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