Aviation Glossary

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ABSOLUTE ALTITUDE Measurable height of an aircraft above the actual terrain.

ABSOLUTE CEILING The maximum altitude above sea level at which an aircraft can maintain level flight under Standard Air conditions.

AGL (Above Ground Level) Altitude expressed as feet above terrain or airport elevation (see MSL).

AILERONS An aircraft control surface hinged to the rear, outer section of the wing for banking (“tilting”) the aircraft. A bank causes an aircraft to turn. Controlled by right or left movement of the control yoke or stick.

AIRCRAFT MANAGEMENT Describes services provided by a management company for an aircraft owner. Under a turn-key management program, all aspects of aircraft preparation, crew management and aircraft maintenance are handled by the management company.

AIRFOIL The shape of any flying surface, but principally a wing, as seen in side-view (cross section).

AIR TRAFFIC CONTROLLER Ground-based personnel responsible for coordinating, directing, and guiding airplanes through their landing and takeoff procedures. They also monitor weather systems that can affect planes and ensure safe travel once planes are airborne.

AIRWORTHINESS DIRECTIVE (AD) Notification to aircraft owner/operators of a known safety issue with a particular model of aircraft, engine, avionics or other system. ADs in the U.S. are issued by the FAA and may be categorized as voluntary, mandatory or emergency.

ALTIMETER A highly sensitive barometer that shows an aircraft’s altitude above mean sea level by measuring atmospheric pressure.

ANGLE OF ATTACK The angle between the airfoil’s chord line and the direction in which the aircraft is currently moving. The amount of lift generated by a wing is directly related to the angle of attack.

APPROACH (DEPARTURE) CONTROL Radar-based air traffic control, associated with the tower at larger airports. Provides traffic separation services from outside the immediate airport area to a distance of about 40 miles.

APRON Hard-surfaced or paved area around a hangar. Also “Ramp.”

ARG/US (Aviation Research Group/U.S., Inc.) A leader in the field of corporate aviation safety and operational information, ARG/US conducts objective, non-intrusive, and fact-based safety analysis for Part 135 charter operators called The CHEQ report (Charter Evaluation and Qualification report). The CHEQ system has three major components: Historical Safety Ratings, Current Aircraft and Pilot Data, and On-Site Safety Audits. Sterling Aviation is ARG/US Gold Rated.

ASOS (Automated Surface Observation System) The primary surface weather observing system in the U.S., supporting aviation operations and weather forecasting. Automated sensors record wind direction and speed, visibility, cloud ceiling, precipitation, etc. Data is sent automatically to the National Weather Service. At many locations, a computer-generated voice broadcasts the minute-by-minute weather reports to pilots on a discrete radio frequency.

ATC (Air Traffic Control) The FAA service providing separation services to participating airborne traffic and clearances to land, take off or taxi at airports with a control tower.

ATIS (Automated Terminal Information System) A continuous broadcast on a separate ATC frequency of an airport's current weather (updated at least hourly). Eliminates controller requirement to read local weather data to each landing or departing aircraft.

AVIONICS The electronic control systems airplanes use for flight such as communications, autopilots, and navigation.

BLOCK RATES A lower “contract rate” for scheduling significant amounts of charter time in advance on a prearranged agreement.

BLOCK FLYING TIME Time between an aircraft first moving from its parking place for the purpose of taking off until it comes to rest on the designated parking position and until all engines are stopped.

CEILING (1) The heights above the earth’s surface of the lowest layers of clouds or obscuring phenomena that is reported as “broken,” “overcast,” or “obscuration,” and not classified as “thin” or “partial.” (2) The maximum height above sea level in Standard Air attainable by an aircraft under given conditions.

CERTIFICATE FAA-issued license (sometimes referred to as ticket, Part 135 license, etc.) to carry passengers for hire.

CHARTER The “renting” of an aircraft with crew for a personal, business, or cargo flight from one point to another.

CHARTER CARD Pre-paid air charter plan, either for a block of charter hours at a pre-defined fee, or a set debit balance in dollars.

CHARTER OPERATOR A company or individual that holds aircraft charter certificates and provides charter services to retail and wholesale customers.

CLASS I NAVIGATION Operation of aircraft under VFR in visual meteorological conditions primarily based on “see and avoid” procedures for all obstacles along the flight route as well as other aircraft.

CLASS II NAVIGATION Any en route flight operation that is not Class I. Often instrument-based navigation dependent on the use of a Long Range Navigation System.

CLEARANCE Formal instructions from air traffic control authorizing a specific route or action (climb or descend, entry into controlled airspace). Pilots may deviate from an ATC clearance in an emergency or when compliance would threaten safety of flight.

CONTRAILS Streaks of condensed water vapor created in the air by aircraft flying at high altitudes; aka vapor trails.

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, B, C, D and E airspace.

CLASS A Airspace Airspace between 18,000 and 60,000 feet MSL over the conterminous United States. IFR clearances are required for all aircraft operating in CLASS A airspace. Formerly called the Positive Control Area.

CLASS B Airspace Airspace area around the busiest U.S. hub airports, typically to a radius of 20 nautical miles and up to 10,000 feet above ground level. Operations within CLASS B airspace require an ATC clearance and at least a Private pilot certificate (local waivers available), radio communication, and an altitude-reporting (Mode C) transponder. Formerly called TCA.

CLASS C Airspace Airspace area around busy U.S. airports (other than CLASS B). Radio contact with approach control is mandatory for all traffic. Typically includes an area from the surface to 1,200 feet AGL out to 5 miles and from 1,200 to 4,000 feet AGL to 10 miles from the airport. Formerly called Airport Radar Service Area (ARSA).

CLASS D Airspace Airspace around an airport with an operating control tower; typically to a radius of 5 miles from the surface to 2,500 feet AGL. Radio contact with the control tower required prior to entry. Formerly called Airport Traffic Area (ATA).

CLASS E Airspace General controlled airspace comprising control areas, transition areas, Victor airways, the Continental Control Area, etc.

CLASS F Airspace International airspace designation not used in the U.S.

CLASS G Airspace Uncontrolled airspace, generally the airspace from the surface up to 700 or 1,200 feet AGL in most of the U.S., but up to as high as 14,500 feet in some remote Western and sparsely populated areas.

CRUISE SPEED The normal speed attained at altitude once the aircraft is no longer climbing and is en route.

DEADHEAD To fly the return leg of a trip without cargo or passengers.

DECISION HEIGHT When flying an aircraft, the height at which a decision must be made during an instrument approach to either continue the approach or to execute a missed approach (abort).

DEPRECIATION Method to account for assets whose value decrease over time because of factors such as age, wear or market conditions. In practice, depreciation serves as an income tax deduction that allows a taxpayer to recover the cost of assets placed in service.

DRAG Resisting force exerted on an aircraft in its line of flight opposite in direction to its motion. Opposite of thrust.

DUTY TIME That portion of the day when a crew member is on duty in any capacity (not just in the air). There are FAA-imposed limits on the amount of time allowed on duty.

E FIS (Electronic Flight Information Systems) Glass cockpit avionics that integrate all flight parameters into one optimized instrument. These modern systems offer enhanced reliability, reduced weight, simplified installation and overall cost savings.

EGPWS (Enhanced Ground Proximity Warning System) Uses aircraft inputs such as position, attitude, air speed and glide slope, which along with internal terrain, obstacles, and airport databases predict a potential conflict between the aircraft's flight path and terrain or an obstacle.

ELEVATOR An aircraft control surface hinged to the rear of the left and right horizontal stabilizer of the aircraft tail. Changes the aircraft pitch attitude nose-up or nose-down, as during climb or descent. Controlled by pushing or pulling on control yoke or stick.

ELT (Emergency Locator Transmitter) A radio transmitter activated automatically by the impact of an accident. Emits a warbling tone on the international emergency frequencies of 121.5 MHz, 243 MHz and (newer models) 406 MHz. ELT signals can be received by nearby FAA facilities, aircraft overhead, and search and rescue (SARSAT) satellites.

EMPTY LEG Also known as “one-way availability.” These are usually posted as available for travel between two airports during a certain time period.
FAA (Federal Aviation Administration) The Department of Transportation's agency for aviation. In addition to regulating airports, aircraft manufacturing and parts certification, aircraft operation and pilot certification ("licensing"), the FAA operates Air Traffic Control, purchases and maintains navigation equipment, certifies airports and aids airport development, among other activities.

FAR (Federal Aviation Regulations) The Federal Aviation Regulations under which aircraft are certified and operate in the U.S. Codified into Parts. (See “Part 91, 135.”)

FBO (Fixed Base Operator) A business operating an airport terminal for non-airline, general aviation aircraft.

FERRY FLIGHT A flight for the purpose of (1) returning an aircraft to base; (2) delivering an aircraft from one location to another; (3) moving an aircraft to and from a maintenance base.

FLAPS Hinged surfaces on the inboard rear of wings, deployed to increase wing curvature (and thus, lift), primarily used to control angle of descent and to decrease landing touchdown speeds.

FLIGHT PLAN Filed by radio, telephone, computer, or in person with Flight Service Stations, a record of aircraft number; type and equipment, estimated time of departure and time en route, route and altitude to be flown, amount of fuel and number of persons aboard, home base and contact phone number; and other information.
  • VFR Flight Plan Voluntary filing for cross-country flights under Visual Flight Rules. For search and rescue use only, it has no air traffic control role.
  • IFR Flight Plan Mandatory filing (at least one-half hour) before a flight under Instrument Flight Rules. Based on flight plan information, ATC can issue (immediately before departure) an IFR clearance to enter clouds or low visibility conditions for instrument rather than visual flight.

FLIGHT STANDARDS DISTRICT OFFICE (FSDO) A regional office of the United States Federal Aviation Administration that concentrates on enforcing regulations. There are over 80 FSDOs nationwide. Contact an FSDO when spotting low-flying aircraft; to report an accident; to obtain aircraft modifications and permits; for certification and surveillance of air operators, air agencies, and airmen; for enforcement and investigation or for aviation safety education and training.

FLIGHT SERVICE STATION (FSS) Air traffic facilities that provide pilot briefing, en route communications and VFR search and rescue services, assist lost aircraft and aircraft in emergency situations, relay ATC clearances, originate Notices or Airmen, 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 trans-border flights.

FLIGHT TIME Portion of the trip actually spent in the air.

FMS (Flight Management System) A computerized avionics component found on commercial and business aircraft. Consists of the Flight Management Computer (FMC), the Auto Flight System (AFS) and the Navigation System, which includes the Inertial Reference System (IRS) and the Global Positioning System (GPS).

FRACTIONAL OWNERSHIP The purchase of a “share” of an aircraft, typically in increments of 1/16th, each of which represents 50 hours of flight time per year. Fractional owners are guaranteed access to an aircraft but not necessarily the one they own. They also pay a monthly maintenance fee and an hourly fee.

FUEL SURCHARGE A charge for the increased price of fuel to cover fuel price increases.

FUSELAGE An aircraft’s main body structure housing the flight crew, passengers, and cargo.

GENERAL AVIATION Portion of civil aviation which encompasses all facets of aviation except air carriers holding a certificate of public convenience and necessity from the Civil Aeronautics Board and large aircraft commercial operators. Includes 92% of U.S. aircraft and more than 65% of U.S. flight hours flown by other than major and regional airlines or the military. Often misunderstood as only small, propeller-driven aircraft. Even a large jet or cargo plane operated under FAR Part 91 can be a general aviation aircraft.

GPS (Global Positioning System) Satellite-based navigation system operated by Department of Defense, providing extremely accurate position, time, and speed information to civilian and military users. Based on a "constellation" of 24 satellites.

GPWS (Ground Proximity Warning System) System designed to alert pilots if their aircraft is in immediate danger of flying into the ground. Also called Ground-Collision Warning System.

GROUND SPEED Actual speed that an aircraft travels over the ground also called “shadow speed.” It combines the aircraft’s air speed and the wind speed relative to the aircraft’s direction of flight.

HANGAR An enclosed structure for housing aircraft. Originated with lake-based floating homes of the original German Zeppelins in which they were “hung” from cables.

HEAVY JETS See “Large-Cabin Jets.”

HORSEPOWER The motive energy required to raise 550 lbs. one foot in one second, friction disregarded.

IFR (Instrument Flight Rules) Rules of the road for flights permitted to penetrate clouds and low visibility conditions by reference to cockpit flight instruments and radio navigation. Aircraft must be equipped and pilots qualified and current for IFR flight. Flight plans and ATC clearances are required. Flights are monitored and traffic separated by Air Traffic Control, usually by radar.

ILS (Instrument Landing System) A precision instrument approach system utilizing radio transmitters at the runway ends which provide precise left-right and up-down indications to the pilot permitting aircraft to land during periods of low ceilings or poor visibility.

IAS (Indicated Airspeed) A direct instrument reading obtained from an air speed indicator uncorrected for altitude, temperature, atmospheric density, or instrument error.

JOINT OWNERSHIP Purchase or lease of a complete aircraft by a relatively small number of owners, often through a partnership or limited liability corporation.

KNOT (Nautical Mile per Hour) Most common measure of aircraft speed equaling 6,080 feet or about 1.15 miles. (For mph, multiply knots by 1.15.)

KTAS True airspeed, in knots.

LAAS Local Area Augmentation System, an enhancement of the Global Positioning System (GPS) providing greater navigation accuracy and system integrity.

LARGE-CABIN JETS The largest size aircraft that doesn't require a major airport runway, while still covering long distances. Typical capacity 9-15 passengers.

LAYOVER A night spent in the middle of the trip in a city other than home base for the aircraft and crew.

LEG Describes one direction of travel between two points. Commonly used in referring to a planned itinerary, it may not indicate all landings such as fuel stops.

LIFT Any aircraft engaged for transport, or the upward force generated by an aircraft wing as it moved through the air.

LIGHT JETS See “Small-Cabin Jets.”

MACH (m.) A number representing the ratio of the speed of an object to the speed of sound in the surrounding air or medium in which it is moving.

MACRS (Modified Accelerated Cost Recovery System) The current method of accelerated asset depreciation required by the United States tax code; enacted in 1986.

MANAGEMENT See “Aircraft Management”

MID-CABIN JETS (Also “Midsize Jets.”) Typical capacity 7-9 passengers.

MSL (Mean Sea Level) The average height of the surface of the sea for all stages of tide; used as a reference for elevations, and differentiated from AGL.

NAUTICAL MILE Historically, a minute of arc along a meridian of the Earth. Since 1929, it has been defined internationally as equivalent to 1,852 meters or 1.15 statute miles.

NONTOWERED AIRPORT An airport without a control tower – the majority of America's 13,000 airports. Only 680 airports have control towers. Non-towered airports are not “uncontrolled.” Pilots follow traffic pattern procedures and self-announce positions and intentions using the Common Traffic Advisory Frequency (CTAF), usually called the UNICOM frequency.

N-NUMBERS Federal Government aircraft registration numbers. U.S.-registered aircraft numbers begin with “N,” Canadian numbers with “C” or “CF,” German numbers with “D,” United Kingdom numbers with “G,” French numbers with “F,” Japanese numbers with “JA,” etc. (See also “Tail Number.”)

NMAC (Near Mid-Air Collision) Defined by FAA as a potential collision situation between aircraft within 500 feet of each other.

NTSB (National Transportation Safety Board) The independent federal agency charged with investigating and finding "probable cause" of transportation accidents.

PART 91, 135 The parts of Federal Aviation Regulations (FARs) covering non-commercial operations such as corporate flight departments (Part 91), and charter carriers (Part 135).

PART 145 REPAIR STATION FAA Certificate allowing an organization to perform maintenance and alterations on U.S.-registered aircraft and engines. A facility must undergo government inspection and comply with the highest levels of conduct, documentation, and credentials to obtain the designation.

PATTERN The path of aircraft traffic around an airfield, at an established height and direction. At tower-controlled fields, air traffic controllers supervise the pattern by radio (or in non-radio or emergency conditions by red and green light signals.

PAYLOAD Anything that an aircraft carries beyond what is required for its operation during flight, theoretically cargo or passengers from which revenue is derived.

PITCH (1) One of the three axes in flight, this specifies the vertical action, the up-and-down movement. (2) The angle of a propeller or rotor blade in relation to its arc; also the distance advanced by a blade in one full rotation.

POSITIONING Ferrying aircraft for departure from other than originating airport.

PROHIBITED AREA An airspace area where flight is prohibited except by prior arrangement with the controlling agency. An example is the P-56 area over downtown Washington, D.C., prohibiting flight over the White House.

PROPJET See “Turboprop.”

RADAR System that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations and terrain.

RAMP The apron or open “tarmac” in front of an FBO or terminal facility. This space is busy, used for deplaning, parking of aircraft, etc.

RELEASE TIME A departure time restriction issued to a pilot by ATC (either directly or through an authorized relay) when necessary to separate a departing aircraft from other traffic.

REPOSITIONING See “Positioning.”

RESTRICTED AREA Airspace that (when “Active” or “Hot”) usually excludes civilian aircraft. Examples: airspace for rocket flights, practice air-to-air combat or ground-based artillery practice. Temporary restricted areas are established for events such as forest fires, natural disasters or major news stories. The “controlling agency” or FAA may authorize flight through a restricted area.

ROLL One of three axes in flight, specifying the action around a central point.

ROTATE In flight, any aircraft will rotate about its center of gravity, a point which is the average location of the mass of the aircraft. The three-dimensional axes that determine the attitude or orientation of an aircraft are described as the yaw, pitch and roll.

RUDDER Aircraft control surface attached to the rear of the vertical stabilizer (fin) of the aircraft tail. Forces the tail left or right, correspondingly “yawing” the aircraft right or left. Rudder movement “coordinates” with the banking of wings to balance a turn. Controlled by left and right rudder (foot) pedals.

SEE-AND-AVOID The FAA requirement that all pilots are ultimately responsible for separation from other aircraft when visual conditions permit spotting traffic. Even IFR flights when operating in visual weather conditions or VFR flights being issued radar advisories are responsible for visual scanning to see-and-avoid other traffic.

SEGMENT Describes the unit of flight between take-off and landing. Sometimes used interchangeably with the term leg.
SLATS Small, aerodynamic surfaces on the leading edge of the wings of fixed aircraft which, when deployed, allow the wing to operate at a higher angle of attack. They are usually used while landing or performing maneuvers but are retracted in normal flight to minimize drag.

SLIPSTREAM The flow of air driven backward by a propeller or downward by a rotor.

SMALL-CABIN JETS Typical capacity 5-8 passengers.

SQUAWK A four-digit number that a pilot dials into his transponder to identify his aircraft to air traffic controllers.

STATUTE MILE A unit of length equal to 5,280 feet.

TAIL NUMBER An airplane’s registration number. (See also “N-Number.”)

TARMAC (1) A bituminous material used in paving; a trade name for Tar MacAdam. (2) An airport surface paved with the substance, especially a runway or an apron at a hangar.

TAWS (Terrain Awareness and Warning System) An advanced type of GPWS that provides the flight crew earlier aural and visual warning of impending terrain, forward looking capability and continued operation in the landing configuration.

TAXI TIME Portion of the trip spent rolling between the gate, terminal, or ramp and runway.

TCA (Terminal Control Area) (See CLASS B Airspace.)

TCAD A proprietary low cost anti-collision system detecting and alerting pilots to nearby transponders but not providing evasive instructions or coordination with other aircraft.

TCAS (Traffic Alert and Collision Avoidance System) A cockpit system to detect other transponder-equipped aircraft, alert pilots, and command/coordinate evasive action between aircraft.

TETRAHEDRON Ground-based, free-rotating, triangular-shaped wind direction indicator, generally placed near a runway.

THRUST The driving force of a propeller or the forward force produced in reaction to the gases expelled rearward from a jet engine. Opposite of drag.

TRAILING EDGE The rearmost edge of an airfoil.

TRANSPONDER An airborne transmitter that responds to ground-based interrogation signals to provide air traffic controllers with more accurate and reliable position information than would be possible with “passive” radar; may also provided air traffic control with an aircraft’s altitude.

TRAFFIC PATTERN A standard rectangular flight pattern around the landing runway at an airport. Includes 45-degree or crosswind entry to the rectangle, with downwind, base and final legs as sides of the rectangle. Standard are 90-degree left turns around the rectangle (non-standard right-hand traffic pattern is noted in Airport Facility Directories) with downwind flown at a specified altitude, usually 1,000 or 1,500 feet above the airport elevation. At airports with a control tower; the pattern may be modified or short-cut according to ATC instructions.

TURBINE Engine that uses compressed air to generate thrust to spin a metal shaft inside the motor. Turbines are vital components in jet engines and also power turboprop aircraft.

TURBOPROP An aircraft in which the propeller is driven by a jet-style turbine rather than a piston.

UNICOM (Universal Communication) A common radio frequency (usually 121.0 mHz) used at controlled (non-tower) airports for local pilot communication. UNICOM is also used by a Fixed Base Operator for general administrative uses, including fuel orders, parking instructions, etc.

VERY LIGHT JETS (VLJ) Newly emerging class of small jet aircraft approved for single-pilot operation with a maximum take-off weight of under 10,000 lb (4,540 kg). Typical capacity 3-7 passengers.

VFR (Visual Flight Rules) A defined set of FAA regulations and “rules of the road” covering operation of aircraft primarily by visual reference to the horizon (for aircraft control) and see-and-avoid procedures (for traffic separation).

VOR (VHF Omnidirectional Range) Ground-based radio navigation aid. More than 1,000 VORs electronically define Victor Airways and Jet Airways, “highways in the sky.” Most IFR and many VFR flights follow airway routes.

VORTICES Regions of high velocity that develop at the tip of a wing as it flies through the air.

WAAS (Wide Area Augmentation System) An enhancement to the GPS system providing greater navigation accuracy and system integrity and permitting GPS to be used for precision instrument approaches to most airports.

WAITING TIME Time that the charted aircraft and crew must wait on the ground during any portion of the trip.

WAKE TURBULENCE Turbulent air condition caused by small, tornado-like horizontal whirlwinds trailing an aircraft’s wingtips (wingtip vortices). Wake turbulence associated with larger aircraft flying at slow speeds (as on take-off or landing approach) is the most severe and can cause loss of control for smaller aircraft following close behind. Controllers use defined separation standards to avoid the problem for take-off, landing, approach and departure operations.

WEATHER MINIMUMS Lowest (worst) visibility conditions under which an aircraft may legally be flown under visual flight rules. When visibility is less than specified minimums, an aircraft must fly under instrument flight rules or not at all.

WIND SHEAR Large changes in either wind speed or direction at different altitudes that can cause sudden gain or loss of airspeed.

WINGLET A small, stabilizing, rudder-like addition to the tips of a wing to control or employ air movement, thereby increasing fuel economy.

YAW One of the three axes in flight, specifying the side-to-side movement of an aircraft on its vertical axis.

YOKE The control wheel of an aircraft, akin to an automobile steering wheel.
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