Airline Handbook Glossary

Aileron
A control surface located on the trailing edge of each wing tip. Deflection of these surfaces controls the roll or bank angle of the aircraft.

Airfoil
Any surface such as an airplane wing, aileron, or rudder designed to obtain a useful reaction from the air moving past it.

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

Altimeter
An instrument which displays the altitude above mean sea level (MSL) of an aircraft.

Artificial Horizon
An instrument which 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.

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.

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

Cockpit Voice Recorder (CVR)
A device that records the sounds audible in the cockpit, as well as all radio transmissions made and received by the aircraft, and all intercom and public address announcements made in the aircraft. It generally is a continuous loop recorder that retains the sounds of the last 30 minutes.

Codesharing
A marketing practice in which two airlines share the same two-letter code used to identify carriers in the computer reservation systems used by travel agents.

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

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.

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

Deregulation
The term commonly used in referring to the Airlines Deregulation Act of 1978, which 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.

Elevator
A control surface, usually on the trailing edge of the horizontal stabilizer, which is used to control the pitch attitude of an aircraft. Movement of the elevator will force the nose of an aircraft up or down.

Empennage
A collective term that refers to all of the various tail surfaces of an aircraft, i,e., the vertical and horizontal stabilizers.

Enplanements
The number of passengers boarding a flight, including origination, stopovers and connections.

En Route Center
Formally known as an Air Route Traffic Control Center (ARTCC), it houses the air traffic controllers and equipment needed to identify and direct aircraft, primarily during the en route portion of their flights.

Essential Air Service
Government subsidized airline service to rural areas of the United States, which continued after the Airline Deregulation Act of 1978.

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 which provides grants from the Airport and Airway Trust Fund for airport development.

Flaps
Control surfaces installed on the trailing edge of a wing and used to increase the amount of lift generated by the wing at slower speeds. Flaps also have the effect of slowing an aircraft during its landing approach.

Flight Data Recorder (FDR)
Records pertinent technical information about a flight. An FDR will record information about the performance of various aircraft systems, as well as the aircraft's speed, altitude, heading and other flight parameters. Like a cockpit voice recorder (CVR), a flight data recorder is designed to withstand the forces of a crash so that its information may be used to reconstruct the circumstances leading up to the accident (in some cases, a digital flight data recorder, or DFDR).

Flight Deck
Also called the cockpit, it the section of an aircraft where pilots sit and control the aircraft.

Flight Plan
A required planning document that covers the expected operational details of a flight such as destination, route, fuel on board, etc. It is filed with the appropriate FAA air traffic control facility. There are both VFR and IFR flight plans. VFR plans are not mandatory.

Flight Service Station (FSS)
An FAA facility that provides specialized flight-related services to pilots. It can provide weather briefings and en route advisories, among other things.

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 cashed in later for free flights or upgrades in cabin service, or in some instances, non-airline services or items.

Fuselage
The main body of an aircraft, cylindrical in shape. It contains the cockpit, main cabin and cargo compartments.

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

Horizontal Stabilizer
The small wings at the rear of an aircraft's fuselage that balance the lift forces generated by the main wings farther forward on the fuselage. The stabilizer also usually contains the elevator.

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.

Instrument Flight Rules (IFR)
Rules governing flight in certain limited visibility and cloud 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)
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.

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

Knot
An abbreviation for one nautical mile per hour. Since a nautical mile is 15 percent longer than a statute mile, a speed expressed in knots is 15% higher than it would be if expressed in miles per hour.

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.

Load Factor
The percentage of available seats that are filled with paying passengers, or the percent of freight capacity that is utilized. Technically, revenue passenger miles divided by available seat miles or cargo ton miles divided by available cargo ton miles.

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

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 approved by the FAA.

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

Nonstop Flight
A flight with no intermediate stops.

Part 121 of the Federal Aviation Regulations
The FAA safety regulations covering operators of aircraft with 10 or more seats.

Part 135 of the Federal Aviation Regulations
The FAA safety regulations covering operators of aircraft with fewer than 10 seats.

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 passenger airfare. It is designed to help pay for airport improvements that enhance safety and capacity and is not revenue for airlines.

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

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

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

Pylon
The part of an aircraft's structure which connects an engine to either a wing or the fuselage.

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.

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

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

Rudder
A control surface, usually installed on the trailing edge of the vertical stabilizer, which controls the yaw motion of the aircraft - that is, the motion of the nose of the aircraft left and right.

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.

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

Slats
Special surfaces attached to or actually part of the leading edge of the wing. During takeoff and landing, they are extended to produce extra lift.

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.

Spoilers
Special panels built into the upper surface of the wing that, when raised, "spoil" the flow of air across the wing and thereby reduce the amount of lift generated. They are useful for expediting a descent.

Stage 2 Aircraft
Term used to describe jets which meet Stage 2 Federal Aviation Regulation (FAR) Part 36 noise parameters on takeoff and landing.

Stage 3 Aircraft
Term used to describe aircraft that meet quieter Stage 3 noise requirements under FAR Part 36.

Stall
Results when a wing exceeds its angle of attack (angle between airfoil and relative flow of wind), the airflow is disrupted, and the wing no longer produces lift, with sudden drop and possible loss of control.

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

Terminal Control Area (TCA)
A designated zone around and above the busiest airports. A flight in TCAs carries stringent requirements for pilot experience, aircraft equipment and communications capability.

Terminal Radar Approach Control Facility (TRACON)
Controls aircraft immediately after and prior to landings and takeoffs, or during the climb and approach phases of flight.

Thrust
The force produced by a jet engine or propeller. As defined by Newtonian physics, it is the forward reaction to the rearward movement of a jet exhaust.

Traffic Alert and Collision Avoidance System (TCAS)
Installed in commercial jets to search for and alert pilots to the presence of other aircraft. Enhanced versions of TCAS also advise pilots on actions to take to avoid aircraft that are getting too close.

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.

Turbofan
A type of jet engine in which a certain portion of the engine's airflow bypasses 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.

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

Vertical Stabilizer
The large "tail" surface normally found on top of the rear of the fuselage. The rudder is usually installed at the trailing edge of the vertical stabilizer.

Visual Flight Rules (VFR)
Rules governing flight during periods of generally good visibility and limited cloud cover. 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.

Widebody 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 Industries' A300 and A310. Technically, any aircraft with a fuselage diameter in excess of 200 inches may be considered a widebody.

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

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
Average revenue per revenue passenger mile or revenue ton mile, expressed in cents per mile.

Yield Management
Also known as revenue management, 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.