Aviation Terminology & Jargon

Aviation Glossary

This glossary defines 491 aviation terms, from aileron to Zulu time. Most definitions are adapted from the FAA's Pilot's Handbook of Aeronautical Knowledge glossary and the FAA Pilot/Controller Glossary, both public documents, and edited for length. Rules are quoted from 14 CFR as published on the eCFR. For terms about specific aircraft types, see the guide to the types of planes.

Jump to a letter: # A B C D E F G H I J K L M N O P R S T U V W Z

#

100-hour inspection: An inspection identical in scope to an annual inspection. Conducted every 100 hours of flight on aircraft of under 12,500 pounds that are used to carry passengers for hire.

A

Absolute altitude: The actual distance between an aircraft and the terrain over which it is flying.

Accelerate-go distance: The distance required to accelerate to V1 with all engines at takeoff power, experience an engine failure at V1, and continue the takeoff on the remaining engine(s). The runway required includes the distance required to climb to 35 feet by which time V2 speed must be attained.

Accelerate-stop distance: The distance required to accelerate to V1 with all engines at takeoff power, experience an engine failure at V1, and abort the takeoff and bring the airplane to a stop using braking action only (use of thrust reversing is not considered).

Acceleration: Force involved in overcoming inertia, and which may be defined as a change in velocity per unit of time.

Adiabatic cooling: A process of cooling the air through expansion. For example, as air moves up slope it expands with the reduction of atmospheric pressure and cools as it expands.

Adjustable-pitch propeller: A propeller with blades whose pitch can be adjusted on the ground with the engine not running, but which cannot be adjusted in flight. Also referred to as a ground adjustable propeller. Sometimes also used to refer to constant-speed propellers that are adjustable in flight.

Adverse yaw: A condition of flight in which the nose of an airplane tends to yaw toward the outside of the turn. This is caused by the higher induced drag on the outside wing, which is also producing more lift. Induced drag is a by-product of the lift associated with the outside wing.

Aerodynamics: The science of the action of air on an object, and with the motion of air on other gases. Aerodynamics deals with the production of lift by the aircraft, the relative wind, and the atmosphere.

Aeronautical chart: A map used in air navigation containing all or part of the following: topographic features, hazards and obstructions, navigation aids, navigation routes, designated airspace, and airports.

Aeronautical decision-making (ADM): A systematic approach to the mental process used by pilots to consistently determine the best course of action in response to a given set of circumstances.

Affirmative: Yes.

Agonic line: An irregular imaginary line across the surface of the Earth along which the magnetic and geographic poles are in alignment, and along which there is no magnetic variation.

Ailerons: Primary flight control surfaces mounted on the trailing edge of an airplane wing, near the tip. Ailerons control roll about the longitudinal axis.

Air mass: An extensive body of air having fairly uniform properties of temperature and moisture.

Air route traffic control center (ARTCC): Provides ATC service to aircraft operating on IFR flight plans within controlled airspace and principally during the en route phase of flight.

Airborne: An aircraft is airborne when all parts of the aircraft are off the ground.

Aircraft: A device that is used, or intended to be used, for flight.

Aircraft altitude: The actual height above sea level at which the aircraft is flying.

Aircraft approach category: A performance grouping of aircraft based on a speed of 1.3 times the stall speed in the landing configuration at maximum gross landing weight.

Airfoil: Any surface, such as a wing, propeller, rudder, or even a trim tab, which provides aerodynamic force when it interacts with a moving stream of air.

AIRMET: Inflight weather advisory issued as an amendment to the area forecast, concerning weather phenomena of operational interest to all aircraft and that is potentially hazardous to aircraft with limited capability due to lack of equipment, instrumentation, or pilot qualifications.

Airplane: An engine-driven, fixed-wing aircraft heavier than air that is supported in flight by the dynamic reaction of air against its wings.

Airplane Flight Manual (AFM): A document developed by the airplane manufacturer and approved by the Federal Aviation Administration (FAA). It is specific to a particular make and model airplane by serial number and it contains operating procedures and limitations.

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

Airport diagram: The section of an instrument approach procedure chart that shows a detailed diagram of the airport. This diagram includes surface features and airport configuration information.

Airport surveillance radar (ASR): Approach control radar used to detect and display an aircraft's position in the terminal area.

Airspeed: Rate of the aircraft's progress through the air.

Airspeed indicator: A differential pressure gauge that measures the dynamic pressure of the air through which the aircraft is flying. Displays the craft's airspeed, typically in knots, to the pilot.

Airway: An airway is based on a centerline that extends from one navigation aid or intersection to another navigation aid (or through several navigation aids or intersections); used to establish a known route for en route procedures between terminal areas.

Airworthiness Certificate: A certificate issued by the FAA to all aircraft that have been proven to meet the minimum standards set down by the Code of Federal Regulations.

Airworthiness Directive: A regulatory notice sent out by the FAA to the registered owner of an aircraft informing the owner of a condition that prevents the aircraft from continuing to meet its conditions for airworthiness.

Alert area: An area in which there is a high volume of pilot training or an unusual type of aeronautical activity.

Alternate airport: An airport designated in an IFR flight plan, providing a suitable destination if a landing at the intended airport becomes inadvisable.

Altimeter: A flight instrument that indicates altitude by sensing pressure changes.

Altimeter setting: Station pressure (the barometric pressure at the location the reading is taken) which has been corrected for the height of the station above sea level.

Ammeter: An instrument installed in series with an electrical load used to measure the amount of current flowing through the load.

Aneroid barometer: An instrument that measures the absolute pressure of the atmosphere by balancing the weight of the air above it against the spring action of the aneroid.

Angle of attack: The angle of attack is the angle at which relative wind meets an airfoil. It is the angle that is formed by the chord of the airfoil and the direction of the relative wind or between the chord line and the flight path.

Angle of incidence: The acute angle formed between the chord line of an airfoil and the longitudinal axis of the aircraft on which it is mounted.

Anhedral: A downward slant from root to tip of an aircraft's wing or horizontal tail surface.

Annual inspection: A complete inspection of an aircraft and engine, required by the Code of Federal Regulations, to be accomplished every 12 calendar months on all certificated aircraft. Only an A&P technician holding an Inspection Authorization can conduct an annual inspection.

Anti-ice: Preventing the accumulation of ice on an aircraft structure via a system designed for that purpose.

Approach lighting system (ALS): Provides lights that will penetrate the atmosphere far enough from touchdown to give directional, distance, and glidepath information for safe transition from instrument to visual flight.

Apron: A defined area on an airport intended for loading or unloading passengers or cargo, refueling, parking or maintenance of aircraft.

Arm: The distance from a datum to the applied force.

Asymmetric thrust: Also known as P-factor. A tendency for an aircraft to yaw to the left due to the descending propeller blade on the right producing more thrust than the ascending blade on the left. This occurs when the aircraft's longitudinal axis is in a climbing attitude in relation to the relative wind.

ATC: Air Traffic Control.

Attitude: The orientation of an aircraft relative to the horizon, described by its pitch and bank.

Attitude and heading reference system (AHRS): A system composed of three-axis sensors that provide heading, attitude, and yaw information for aircraft. AHRS are designed to replace traditional mechanical gyroscopic flight instruments and provide superior reliability and accuracy.

Attitude indicator: The foundation for all instrument flight, this instrument reflects the airplane's attitude in relation to the horizon.

Attitude instrument flying: Controlling the aircraft by reference to the instruments rather than by outside visual cues.

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

Automated Weather Observing System (AWOS): Automated weather reporting system consisting of various sensors, a processor, a computer-generated voice subsystem, and a transmitter to broadcast weather data.

Automatic dependent surveillance-broadcast (ADS-B): A function on an aircraft or vehicle that periodically broadcasts its state vector (i.e., horizontal and vertical position, horizontal and vertical velocity) and other information.

Automatic direction finder (ADF): Electronic navigation equipment that operates in the low- and medium-frequency bands. Used in conjunction with the ground-based nondirectional beacon (NDB), the instrument displays the number of degrees clockwise from the nose of the aircraft to the station being received.

Automatic terminal information service (ATIS): The continuous broadcast of recorded non-control information in selected terminal areas. Its purpose is to improve controller effectiveness and relieve frequency congestion by automating repetitive transmission of essential but routine information.

Autopilot: An automatic flight control system which keeps an aircraft in level flight or on a set course. Automatic pilots can be directed by the pilot, or they may be coupled to a radio navigation signal.

Aviation medical examiner (AME): A physician with training in aviation medicine designated by the Civil Aerospace Medical Institute (CAMI).

Aviation Routine Weather Report (METAR): Observation of current surface weather reported in a standard international format.

Axes of an aircraft: Three imaginary lines that pass through an aircraft's center of gravity. The axes can be considered as imaginary axles around which the aircraft rotates. The three axes pass through the center of gravity at 90° angles to each other.

B

Back course (BC): The reciprocal of the localizer course for an ILS. When flying a back-course approach, an aircraft approaches the instrument runway from the end at which the localizer antennas are installed.

Balance tab: An auxiliary control mounted on a primary control surface, which automatically moves in the direction opposite the primary control to provide an aerodynamic assist in the movement of the control.

Barometric scale: A scale on the dial of an altimeter to which the pilot sets the barometric pressure level from which the altitude shown by the pointers is measured.

Base leg: A flight path at right angles to the landing runway, off its approach end, running from the downwind leg to the extended runway centerline.

Basic empty weight (GAMA): Basic empty weight includes the standard empty weight plus optional and special equipment that has been installed.

Bernoulli's principle: A principle that explains how the pressure of a moving fluid varies with its speed of motion. An increase in the speed of movement causes a decrease in the fluid's pressure.

Biplanes: Airplanes with two sets of wings.

Block altitude: A block of altitudes assigned by ATC to allow altitude deviations, for example "maintain block altitude 9 to 11 thousand."

Bypass ratio: The ratio of the mass airflow in pounds per second through the fan section of a turbofan engine to the mass airflow that passes through the gas generator portion of the engine.

C

Cabin altitude: Cabin pressure in terms of equivalent altitude above sea level.

Calibrated airspeed: The speed at which the aircraft is moving through the air, found by correcting IAS for instrument and position errors.

Camber: The camber of an airfoil is the characteristic curve of its upper and lower surfaces. The upper camber is more pronounced, while the lower camber is comparatively flat. This causes the velocity of the airflow immediately above the wing to be much higher than that below the wing.

Canard: A horizontal surface mounted ahead of the main wing to provide longitudinal stability and control. It may be a fixed, movable, or variable geometry surface, with or without control surfaces.

Canard configuration: A configuration in which the span of the forward wings is substantially less than that of the main wing.

Category (aircraft): For pilot certification, a broad classification of aircraft such as airplane, rotorcraft, glider and lighter-than-air. For aircraft certification, a grouping by intended use or operating limits, such as normal, utility or acrobatic (14 CFR 1.1).

Ceiling: The height above the earth's surface of the lowest layer of clouds, which is reported as broken or overcast, or the vertical visibility into an obscuration.

Center of gravity (CG): The point at which an airplane would balance if it were possible to suspend it at that point. It is the mass center of the airplane, or the theoretical point at which the entire weight of the airplane is assumed to be concentrated.

Center of gravity limits: The specified forward and aft points within which the CG must be located during flight. These limits are indicated on pertinent airplane specifications.

Center of pressure: A point along the wing chord line where lift is considered to be concentrated. For this reason, the center of pressure is commonly referred to as the center of lift.

Centrifugal force: An outward force that opposes centripetal force, resulting from the effect of inertia during a turn.

Chart Supplement: An FAA publication, formerly the Airport/Facility Directory, with information on airports, communications and navigation aids.

Checklist: A tool that is used as a human factors aid in aviation safety. It is a systematic and sequential list of all operations that must be performed to properly accomplish a task.

Chord line: An imaginary straight line drawn through an airfoil from the leading edge to the trailing edge.

Circling approach: A maneuver initiated by the pilot to align the aircraft with a runway for landing when a straightin landing from an instrument approach is not possible or is not desirable.

Class (aircraft): For pilot certification, a classification within a category of aircraft with similar operating characteristics, such as single-engine land or multiengine sea (14 CFR 1.1 and 61.5).

Class A airspace: Airspace from 18,000 feet MSL up to and including FL 600. All aircraft in it must operate under IFR.

Class B airspace: Airspace from the surface to 10,000 feet MSL surrounding the nation's busiest airports in terms of IFR operations or passenger numbers.

Class C airspace: Airspace from the surface to 4,000 feet above the airport elevation (charted in MSL) surrounding those airports having an operational control tower, serviced by radar approach control, and having a certain number of IFR operations or passenger numbers.

Class D airspace: Airspace from the surface to 2,500 feet above the airport elevation (charted in MSL) surrounding those airports that have an operational control tower.

Class E airspace: Controlled airspace that is not Class A, B, C or D, extending upward from the surface or from a designated altitude.

Class G airspace: Airspace that is uncontrolled, except when associated with a temporary control tower, and has not been designated as Class A, Class B, Class C, Class D, or Class E airspace.

Clean configuration: A configuration in which all flight control surfaces have been placed to create minimum drag. In most aircraft this means flaps and gear retracted.

Clear ice: Glossy, clear, or translucent ice formed by the relatively slow freezing of large, supercooled water droplets.

Clearance: ATC permission for an aircraft to proceed under specified traffic conditions within controlled airspace, for the purpose of providing separation between known aircraft.

Clearance delivery: Control tower position responsible for transmitting departure clearances to IFR flights.

Clearance limit: The fix, point, or location to which an aircraft is cleared when issued an air traffic clearance.

Clearance void time: Used by ATC, the time at which the departure clearance is automatically canceled if takeoff has not been made. The pilot must obtain a new clearance or cancel the IFR flight plan if not off by the specified time.

Cleared for the option: ATC authorization to make a touch-and-go, low approach, missed approach, stop-and-go or full-stop landing at the pilot's discretion. It is normally used in training.

Cleared to land: ATC authorization for an aircraft to land. It is based on known traffic and known physical airport conditions.

Closed traffic: Successive takeoffs and landings, or low approaches, where the aircraft does not leave the traffic pattern.

Coefficient of lift (CL): The ratio between lift pressure and dynamic pressure.

Cold front: The boundary between two air masses where cold air is replacing warm air.

Common traffic advisory frequency (CTAF): A frequency used for airport advisory practices when operating to or from an airport without an operating control tower. It may be a UNICOM, Multicom, FSS or tower frequency.

Compass locator: A low-power, low- or medium-frequency (L/MF) radio beacon installed at the site of the outer or middle marker of an ILS.

Compass rose: A small circle graduated in 360° increments, to show direction expressed in degrees.

Complex aircraft: An aircraft with retractable landing gear, flaps, and a controllable-pitch propeller.

Compressor stall: In gas turbine engines, a condition in an axial-flow compressor in which one or more stages of rotor blades fail to pass air smoothly to the succeeding stages. A stall condition is caused by a pressure ratio that is incompatible with the engine rpm.

Condensation: A change of state of water from a gas (water vapor) to a liquid.

Configuration: This is a general term, which normally refers to the position of the landing gear and flaps.

Constant-speed propeller: A controllable-pitch propeller whose pitch is automatically varied in flight by a governor to maintain a constant rpm in spite of varying air loads.

Controllability: A measure of the response of an aircraft relative to the pilot's flight control inputs.

Controllable-pitch propeller (CPP): A type of propeller with blades that can be rotated around their long axis to change their pitch. If the pitch can be set to negative values, the reversible propeller can also create reverse thrust for braking or reversing without the need of changing the direction of shaft revolutions.

Controlled airspace: An airspace of defined dimensions within which ATC service is provided to IFR and VFR flights in accordance with the airspace classification. It includes Class A, Class B, Class C, Class D, and Class E airspace.

Convective SIGMET: Weather advisory concerning convective weather significant to the safety of all aircraft, including thunderstorms, hail, and tornadoes.

Coordinated flight: Flight with a minimum disturbance of the forces maintaining equilibrium, established via effective control use.

Coriolis illusion: The illusion of rotation or movement in an entirely different axis, caused by an abrupt head movement, while in a prolonged constant-rate turn that has ceased to stimulate the brain's motion sensing system.

Course: The intended direction of flight in the horizontal plane measured in degrees from north.

Cowl flaps: Shutter-like devices arranged around certain air-cooled engine cowlings, which may be opened or closed to regulate the flow of air around the engine.

Crew resource management (CRM): The application of team management concepts in the flight deck environment. It was initially known as cockpit resource management, but as CRM programs evolved to include cabin crews, maintenance personnel, and others, the phrase "crew resource management" was adopted.

Critical altitude: The maximum altitude under standard atmospheric conditions at which a turbocharged engine can produce its rated horsepower.

Critical angle of attack: The angle of attack at which a wing stalls regardless of airspeed, flight attitude, or weight.

Cross-check: The first fundamental skill of instrument flight, also known as "scan," the continuous and logical observation of instruments for attitude and performance information.

Crosswind leg: A flight path at right angles to the landing runway, off its takeoff end.

D

Dark adaptation: Physical and chemical adjustments of the eye that make vision possible in relative darkness.

Datum (reference datum): An imaginary vertical plane or line from which all measurements of arm are taken. The datum is established by the manufacturer. Once the datum has been selected, all moment arms and the location of CG range are measured from this point.

Dead reckoning: Navigation of an airplane solely by means of computations based on airspeed, course, heading, wind direction and speed, groundspeed, and elapsed time.

Deadstick: Flying or landing without engine power. It is slang, and the airplane is flown as a glider.

Decision altitude (DA): A specified altitude on an approach with vertical guidance, charted in feet MSL, at which a missed approach must begin if the required visual references have not been established.

Decision height (DH): A specified height on an approach with vertical guidance, charted above the threshold elevation, at which the pilot must decide to continue the approach or fly the missed approach.

Deice: The act of removing ice accumulation from an aircraft structure.

Density altitude: Pressure altitude corrected for nonstandard temperature. Density altitude is used in computing the performance of an aircraft and its engines.

Departure procedure (DP): Preplanned IFR ATC departure, published for pilot use, in textual and graphic format.

Detonation: The sudden release of heat energy from fuel in an aircraft engine caused by the fuel-air mixture reaching its critical pressure and temperature. Detonation occurs as a violent explosion rather than a smooth burning process.

Deviation: A magnetic compass error caused by local magnetic fields within the aircraft. Deviation error is different on each heading.

Dew: Moisture that has condensed from water vapor. Usually found on cooler objects near the ground, such as grass, as the near-surface layer of air cools faster than the layers of air above it.

Dewpoint: The temperature at which air reaches a state where it can hold no more water.

Differential Global Positioning System (DGPS): A system that improves the accuracy of Global Navigation Satellite Systems (GNSS) by measuring changes in variables to provide satellite positioning corrections.

Dihedral: The positive acute angle between the lateral axis of an airplane and a line through the center of a wing or horizontal stabilizer. Dihedral contributes to the lateral stability of an airplane.

Directional stability: Stability about the vertical axis of an aircraft, whereby an aircraft tends to return, on its own, to flight aligned with the relative wind when disturbed from that equilibrium state. The vertical tail is the primary contributor to directional stability, causing an airplane in flight to align with the relative wind.

Distance measuring equipment (DME): A pulse-type electronic navigation system that shows the pilot, by an instrument-panel indication, the number of nautical miles between the aircraft and a ground station or waypoint.

Distress: A condition of being threatened by serious or imminent danger and of requiring immediate assistance.

DME arc: A flight track that is a constant distance from the station or waypoint.

Downwind leg: A flight path parallel to the landing runway in the opposite direction of landing.

Drag: The net aerodynamic force parallel to the relative wind, usually the sum of two components: induced drag and parasite drag.

Drift angle: Angle between heading and track.

Dutch roll: A combination of rolling and yawing oscillations that normally occurs when the dihedral effects of an aircraft are more powerful than the directional stability. Usually dynamically stable but objectionable in an airplane because of the oscillatory nature.

Dynamic hydroplaning: A condition that exists when landing on a surface with standing water deeper than the tread depth of the tires. When the brakes are applied, there is a possibility that the brake will lock up and the tire will ride on the surface of the water, much like a water ski.

Dynamic stability: The property of an aircraft that causes it, when disturbed from straight-and-level flight, to develop forces or moments that restore the original condition of straight and level.

E

Elevator: The horizontal, movable primary control surface in the tail section, or empennage, of an airplane. The elevator is hinged to the trailing edge of the fixed horizontal stabilizer.

Elevator illusion: The sensation of being in a climb or descent, caused by the kind of abrupt vertical accelerations that result from up- or downdrafts.

Emergency: A distress or urgent condition.

Emergency locator transmitter (ELT): A transmitter on an aircraft that sends a distress signal after a crash. 14 CFR 91.207 requires one on most U.S.-registered civil airplanes, with exceptions.

Empennage: The section of the airplane that consists of the vertical stabilizer, the horizontal stabilizer, and the associated control surfaces.

Encoding altimeter: A special type of pressure altimeter used to send a signal to the air traffic controller on the ground, showing the pressure altitude the aircraft is flying.

Exhaust gas temperature (EGT): The temperature of the exhaust gases as they leave the cylinders of a reciprocating engine or the turbine section of a turbine engine.

Expect-further-clearance (EFC): The time a pilot can expect to receive clearance beyond a clearance limit.

Expedite: Used by ATC when prompt compliance is needed to avoid an imminent situation. An expedite climb or descent normally means the approximate best rate should be used.

F

Federal airways: Class E airspace areas that extend upward from 1,200 feet to, but not including, 18,000 feet MSL, unless otherwise specified.

Final approach: The part of an instrument approach procedure in which alignment and descent for landing are accomplished.

Final approach (traffic pattern): A flight path in the direction of landing along the extended runway centerline, from the base leg to the runway.

Final approach fix (FAF): The fix from which the IFR final approach to an airport is executed, and which identifies the beginning of the final approach segment. An FAF is designated on government charts by a Maltese cross symbol for nonprecision approaches, and a lightning bolt symbol for precision approaches.

Fixed-pitch propellers: Propellers with fixed blade angles. Fixed-pitch propellers are designed as climb propellers, cruise propellers, or standard propellers.

Flameout: A condition in the operation of a gas turbine engine in which the fire in the engine goes out due to either too much or too little fuel sprayed into the combustors.

Flaps: Hinged portion of the trailing edge between the ailerons and fuselage. In some aircraft ailerons and flaps are interconnected to produce full-span "flaperons." In either case, flaps change the lift and drag on the wing.

Flight following: Radar-identified aircraft are observed while the pilot provides primary navigation, and the controller keeps the aircraft's identity matched to its radar target.

Flight level (FL): A measure of altitude in hundreds of feet, used above 18,000 feet with the altimeter set to 29.92 inches of mercury.

Flight management system (FMS): Provides pilot and crew with highly accurate and automatic long-range navigation capability, blending available inputs from long- and shortrange sensors.

Flight plan: Information about an intended flight, filed with a flight service station or an ATC facility, orally or in writing.

Flight review: Under 14 CFR 61.56, at least 1 hour of flight training and 1 hour of ground training, including a review of the Part 91 rules and the maneuvers the instructor chooses. A pilot needs one within the preceding 24 calendar months to act as pilot in command.

Fog: Cloud made of tiny water droplets and based at the surface. Unlike drizzle, the droplets stay suspended in the air.

Force (F): The energy applied to an object that attempts to cause the object to change its direction, speed, or motion. In aerodynamics, it is expressed as F, T (thrust), L (lift), W (weight), or D (drag), usually in pounds.

Foreign object damage (FOD): Damage to a gas turbine engine caused by some object being sucked into the engine while it is running. Debris from runways or taxiways can cause foreign object damage during ground operations, and the ingestion of ice and birds can cause FOD in flight.

Form drag: The drag created because of the shape of a component or the aircraft.

Front: The boundary between two different air masses.

Frost: Ice crystal deposits formed by sublimation when temperature and dewpoint are below freezing.

Fuel load: The expendable part of the load of the airplane. It includes only usable fuel, not fuel required to fill the lines or that which remains trapped in the tank sumps.

Fuselage: The section of the airplane that consists of the cabin and/or cockpit, containing seats for the occupants and the controls for the airplane.

G

Glider: A heavier-than-air aircraft supported in flight by the dynamic reaction of the air against its lifting surfaces, whose free flight does not depend principally on an engine (14 CFR 1.1).

Glideslope (GS): Part of the ILS that projects a radio beam upward at an angle of approximately 3° from the approach end of an instrument runway. The glideslope provides vertical guidance to aircraft on the final approach course for the aircraft to follow when making an ILS approach along the localizer path.

Global positioning system (GPS): Navigation system that uses satellite rather than ground-based transmitters for location information.

Go around: An instruction to abandon the approach to landing. A VFR aircraft should overfly the runway while climbing to traffic pattern altitude, and an IFR aircraft flies the published missed approach unless ATC says otherwise.

Graveyard spiral: The illusion of the cessation of a turn while still in a prolonged, coordinated, constant rate turn, which can lead a disoriented pilot to a loss of control of the aircraft.

Great circle route: The shortest distance across the surface of a sphere (the Earth) between two points on the surface.

Ground effect: The condition of slightly increased air pressure below an airplane wing or helicopter rotor system that increases the amount of lift produced. It exists within approximately one wing span or one rotor diameter from the ground.

Ground proximity warning system (GPWS): A system designed to determine an aircraft's clearance above the Earth and provides limited predictability about aircraft position relative to rising terrain.

Groundspeed: Speed over the ground, either closing speed to the station or waypoint, or speed over the ground in whatever direction the aircraft is going at the moment, depending upon the navigation system used.

Gyroplane: A rotorcraft whose rotors are not engine-driven except for initial starting, and are turned by the air as the aircraft moves, while a propeller provides propulsion (14 CFR 1.1).

Gyroscopic precession: An inherent quality of rotating bodies, which causes an applied force to be manifested 90° in the direction of rotation from the point where the force is applied.

H

Handoff: The transfer of radar identification of an aircraft from one controller to another, when the aircraft will enter the second controller's airspace and radio communications will transfer.

Hazardous attitudes: Five aeronautical decision-making attitudes that may contribute to poor pilot judgment: antiauthority, impulsivity, invulnerability, machismo, and resignation.

Hazardous Inflight Weather Advisory Service (HIWAS): An en route flight service station service that provides continuously updated automated broadcasts of hazardous weather within 150 nautical miles of selected VORs, available only in the conterminous 48 states.

Head-up display (HUD): A special type of flight viewing screen that allows the pilot to watch the flight instruments and other data while looking through the windshield of the aircraft for other traffic, the approach lights, or the runway.

Heading: The direction in which the nose of the aircraft is pointing during flight.

Heading indicator: An instrument which senses airplane movement and displays heading based on a 360° azimuth, with the final zero omitted. The heading indicator, also called a directional gyro (DG), is fundamentally a mechanical instrument designed to facilitate the use of the magnetic compass.

Height above touchdown elevation (HAT): The DA/DH or MDA above the highest runway elevation in the touchdown zone (first 3,000 feet of the runway).

High performance aircraft: An aircraft with an engine of more than 200 horsepower.

Hobbs meter: A meter that records the time an aircraft's engine runs, often used to bill aircraft rentals. It is different from the tach meter, which runs more slowly at low power.

Holding: A predetermined maneuver that keeps aircraft within a specified airspace while awaiting further clearance from ATC.

Holding pattern: A racetrack pattern, involving two turns and two legs, used to keep an aircraft within a prescribed airspace with respect to a geographic fix. A standard pattern uses right turns; nonstandard patterns use left turns.

Homing: Flying the aircraft on any heading required to keep the needle pointing to the 0° relative bearing position.

Horizontal situation indicator (HSI): A flight navigation instrument that combines the heading indicator with a CDI, in order to provide the pilot with better situational awareness of location with respect to the courseline.

Horsepower: The term, originated by inventor James Watt, means the amount of work a horse could do in one second. One horsepower equals 550 foot-pounds per second, or 33,000 foot-pounds per minute.

Human factors: A multidisciplinary field encompassing the behavioral and social sciences, engineering, and physiology, to consider the variables that influence individual and crew performance for the purpose of optimizing human performance and reducing errors.

Hydroplaning: A condition that exists when landing on a surface with standing water deeper than the tread depth of the tires. When the brakes are applied, there is a possibility that the brake will lock up and the tire will ride on the surface of the water, much like a water ski.

Hyperventilation: Occurs when an individual is experiencing emotional stress, fright, or pain, and the breathing rate and depth increase, although the carbon dioxide level in the blood is already at a reduced level.

Hypoxia: A state of oxygen deficiency in the body sufficient to impair functions of the brain and other organs.

I

Ident: Air Traffic Control request for a pilot to push the button on the transponder to identify return on the controller's scope.

ILS categories: Categories I, II and III of ILS approach, with progressively lower minimums. Categories II and III need special authorization.

Indicated airspeed (IAS): Shown on the dial of the instrument airspeed indicator on an aircraft. Indicated airspeed (IAS) is the airspeed indicator reading uncorrected for instrument, position, and other errors.

Indicated altitude: The altitude read directly from the altimeter (uncorrected) when it is set to the current altimeter setting.

Induced drag: Drag caused by the same factors that produce lift; its amount varies inversely with airspeed. As airspeed decreases, the angle of attack must increase, in turn increasing induced drag.

Induction icing: A type of ice in the induction system that reduces the amount of air available for combustion. The most commonly found induction icing is carburetor icing.

Initial approach fix (IAF): The fix depicted on IAP charts where the instrument approach procedure (IAP) begins unless otherwise authorized by ATC.

Inoperative components: Higher minimums are prescribed when the specified visual aids are not functioning; this information is listed in the Inoperative Components Table found in the United States Terminal Procedures Publications.

Instrument approach procedures (IAP): A series of predetermined maneuvers for the orderly transfer of an aircraft under IFR from the beginning of the initial approach to a landing or to a point from which a landing may be made visually.

Instrument flight rules (IFR): Rules and regulations established by the Federal Aviation Administration to govern flight under conditions in which flight by outside visual reference is not safe. IFR flight depends upon flying by reference to instruments in the flight deck, and navigation is accomplished by reference to electronic signals.

Instrument landing system (ILS): An electronic system that provides both horizontal and vertical guidance to a specific runway, used to execute a precision instrument approach procedure.

Instrument meteorological conditions (IMC): Meteorological conditions expressed in terms of visibility, distance from clouds, and ceiling less than the minimums specified for visual meteorological conditions, requiring operations to be conducted under IFR.

Instrument takeoff: Using the instruments rather than outside visual cues to maintain runway heading and execute a safe takeoff.

Interference drag: Drag generated by the collision of airstreams creating eddy currents, turbulence, or restrictions to smooth flow.

International Civil Aviation Organization (ICAO): The United Nations agency for developing the principles and techniques of international air navigation, and fostering planning and development of international civil air transport.

Inversion: An increase in temperature with altitude.

Isobars: Lines which connect points of equal barometric pressure.

J

Jet route: A route designated to serve flight operations from 18,000 feet MSL up to and including FL 450.

Jet stream: A high-velocity narrow stream of winds, usually found near the upper limit of the troposphere, which flows generally from west to east.

K

Knot: The knot is a unit of speed equal to one nautical mile (1.852 km) per hour, approximately 1.151 mph.

Kollsman window: A barometric scale window of a sensitive altimeter used to adjust the altitude for the altimeter setting.

L

Land and hold short operations (LAHSO): Operations where a landing aircraft is instructed to hold short of an intersecting runway or taxiway, a set point or an approach or departure flight path, so simultaneous operations can take place.

Land as soon as possible: Land without delay at the nearest suitable area, such as an open field, at which a safe approach and landing is assured.

Land as soon as practical: The landing site and duration of flight are at the discretion of the pilot. Extended flight beyond the nearest approved landing area is not recommended.

Land breeze: A coastal breeze flowing from land to sea caused by temperature differences when the sea surface is warmer than the adjacent land. The land breeze usually occurs at night and alternates with the sea breeze that blows in the opposite direction by day.

Land immediately: The urgency of the landing is paramount. The primary consideration is to ensure the survival of the occupants. Landing in trees, water, or other unsafe areas should be considered only as a last resort.

Lateral axis: An imaginary line passing through the center of gravity of an airplane and extending across the airplane from wingtip to wingtip.

Lateral stability (rolling): The stability about the longitudinal axis of an aircraft. Rolling stability or the ability of an airplane to return to level flight due to a disturbance that causes one of the wings to drop.

Latitude: Measurement north or south of the equator in degrees, minutes, and seconds. Lines of latitude are also referred to as parallels.

Leading edge: The part of an airfoil that meets the airflow first.

Leading edge devices: High lift devices which are found on the leading edge of the airfoil. The most common types are fixed slots, movable slats, and leading edge flaps.

Leading-edge flap: A portion of the leading edge of an airplane wing that folds downward to increase the camber, lift, and drag of the wing. The leading-edge flaps are extended for takeoffs and landings to increase the amount of aerodynamic lift that is produced at any given airspeed.

Lift: A component of the total aerodynamic force on an airfoil and acts perpendicular to the relative wind.

Light-sport aircraft: An aircraft that meets the light-sport category eligibility rules in 14 CFR 22.100. For an airplane, that includes up to four seats, a stall speed of no more than 61 knots CAS and a non-pressurized cabin.

Limit load factor: Amount of stress, or load factor, that an aircraft can withstand before structural damage or failure occurs.

Load factor: The ratio of a specified load to the total weight of the aircraft. The specified load is expressed in terms of any of the following: aerodynamic forces, inertial forces, or ground or water reactions.

Localizer (LOC): The portion of an ILS that gives left/right guidance information down the centerline of the instrument runway for final approach.

Localizer-type directional aid (LDA): A NAVAID used for nonprecision instrument approaches with utility and accuracy comparable to a localizer but which is not a part of a complete ILS and is not aligned with the runway. Some LDAs are equipped with a glideslope.

Longitude: Measurement east or west of the Prime Meridian in degrees, minutes, and seconds. The Prime Meridian is 0° longitude and runs through Greenwich, England. Lines of longitude are also referred to as meridians.

Longitudinal axis: An imaginary line through an aircraft from nose to tail, passing through its center of gravity. The longitudinal axis is also called the roll axis of the aircraft. Movement of the ailerons rotates an airplane about its longitudinal axis.

Longitudinal stability (pitching): Stability about the lateral axis. A desirable characteristic of an airplane whereby it tends to return to its trimmed angle of attack after displacement.

Low approach: An approach over an airport or runway after an instrument or VFR approach, including a go-around, where the pilot intentionally does not touch down.

Lubber line: The reference line used in a magnetic compass or heading indicator.

M

Mach number: The ratio of the true airspeed of the aircraft to the speed of sound in the same atmospheric conditions, named in honor of Ernst Mach, late 19th century physicist.

Magnetic bearing (MB): The direction to or from a radio transmitting station measured relative to magnetic north.

Magnetic compass: A device for determining direction measured from magnetic north.

Magnetic dip: A vertical attraction between a compass needle and the magnetic poles. The closer the aircraft is to a pole, the more severe the effect.

Magnetic heading (MH): The direction an aircraft is pointed with respect to magnetic north.

Magneto: A self-contained, engine-driven unit that supplies electrical current to the spark plugs; completely independent of the airplane's electrical system. Normally there are two magnetos per engine.

Mandatory altitude: An altitude depicted on an instrument approach chart with the altitude value both underscored and overscored. Aircraft are required to maintain altitude at the depicted value.

Maneuvering speed (VA): The design maneuvering speed. Operating at or below design maneuvering speed does not provide structural protection against multiple full control inputs in one axis or full control inputs in more than one axis at the same time.

Manifold absolute pressure: The absolute pressure of the fuel/air mixture within the intake manifold, usually indicated in inches of mercury.

Marker beacon: A low-powered transmitter that directs its signal upward in a small, fan-shaped pattern. Used along the flight path when approaching an airport for landing, marker beacons indicate both aurally and visually when the aircraft is directly over the facility.

Maximum landing weight: The greatest weight that an airplane normally is allowed to have at landing.

Maximum ramp weight: The total weight of a loaded aircraft, including all fuel. It is greater than the takeoff weight due to the fuel that will be burned during the taxi and runup operations. Ramp weight may also be referred to as taxi weight.

Maximum takeoff weight: The maximum allowable weight for takeoff.

Mayday: The international radiotelephony distress signal. Repeated three times, it indicates imminent and grave danger and that immediate assistance is requested.

Mean aerodynamic chord (MAC): The average distance from the leading edge to the trailing edge of the wing.

Mean sea level: The average height of the surface of the sea at a particular location for all stages of the tide over a 19-year period.

Microburst: A strong downdraft which normally occurs over horizontal distances of 1 NM or less and vertical distances of less than 1,000 feet. In spite of its small horizontal scale, an intense microburst could induce windspeeds greater than 100 knots and downdrafts as strong as 6,000 feet per minute.

Military operations area (MOA): Airspace established for the purpose of separating certain military training activities from IFR traffic.

Military training route (MTR): Airspace of defined vertical and lateral dimensions established for the conduct of military training at airspeeds in excess of 250 knots indicated airspeed (KIAS).

Minimum descent altitude (MDA): The lowest altitude (in feet MSL) to which descent is authorized on final approach, or during circle-to-land maneuvering in execution of a nonprecision approach.

Minimum en route altitude (MEA): The lowest published altitude between radio fixes that ensures acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes.

Minimum equipment list (MEL): A list developed for larger aircraft that outlines equipment that can be inoperative for various types of flight including IFR and icing conditions. This list is based on the master minimum equipment list (MMEL) developed by the FAA and must be approved by the FAA for use. It is specific to an individual aircraft make and model.

Minimum fuel: A term meaning the fuel supply has reached a state where the aircraft can accept little or no delay on reaching the destination. It is not an emergency, but one is possible if any undue delay occurs.

Minimum obstruction clearance altitude (MOCA): The lowest published altitude in effect between radio fixes on VOR airways, off-airway routes, or route segments, which meets obstacle clearance requirements for the entire route segment and which ensures acceptable navigational signal coverage only within 25 statute (22 nautical) miles of a VOR.

Minimum vectoring altitude (MVA): An IFR altitude lower than the minimum en route altitude (MEA) that provides terrain and obstacle clearance.

Missed approach: A maneuver conducted by a pilot when an instrument approach cannot be completed to a landing.

Missed approach point (MAP): A point prescribed in each instrument approach at which a missed approach procedure shall be executed if the required visual reference has not been established.

Mode C: Altitude reporting transponder mode.

Moment: The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches (lb-in). Total moment is the weight of the airplane multiplied by the distance between the datum and the CG.

Moment arm: The distance from a datum to the applied force.

Monocoque: A shell-like fuselage design in which the stressed outer skin is used to support the majority of imposed stresses. Monocoque fuselage design may include bulkheads but not stringers.

Monoplanes: Airplanes with a single set of wings.

N

Nacelle: A streamlined enclosure on an aircraft in which an engine is mounted. On multiengine propeller-driven airplanes, the nacelle is normally mounted on the leading edge of the wing.

National Airspace System (NAS): The common network of United States airspace--air navigation facilities, equipment and services, airports or landing areas; aeronautical charts, information and services; rules, regulations and procedures, technical information; and manpower and material.

National Transportation Safety Board (NTSB): A United States Government independent organization responsible for investigations of accidents involving aviation, highways, waterways, pipelines, and railroads in the United States. NTSB is charged by congress to investigate every civil aviation accident in the United States.

NAVAID: Navigational aid.

Negative: No, permission not granted, or that is not correct.

No-gyro approach: A radar approach that may be used in case of a malfunctioning gyro-compass or directional gyro. Instead of providing the pilot with headings to be flown, the controller observes the radar track and issues control instructions "turn right/left" or "stop turn," as appropriate.

Nondirectional radio beacon (NDB): A ground-based radio transmitter that transmits radio energy in all directions.

Nonprecision approach: A standard instrument approach procedure in which only horizontal guidance is provided.

NORDO: Short for no radio. It describes an aircraft with no radio, or with a radio that has failed.

Notice to Airmen (NOTAM): A notice filed with an aviation authority to alert aircraft pilots of any hazards en route or at a specific location. The authority in turn provides means of disseminating relevant NOTAMs to pilots.

O

Obstacle departure procedures (ODP): A preplanned instrument flight rule (IFR) departure procedure printed for pilot use in textual or graphic form to provide obstruction clearance via the least onerous route from the terminal area to the appropriate en route structure.

Occluded front: A frontal occlusion occurs when a fastmoving cold front catches up with a slow moving warm front. The difference in temperature within each frontal system is a major factor in determining whether a cold or warm front occlusion occurs.

Orientation: Awareness of the position of the aircraft and of oneself in relation to a specific reference point.

Outer marker: A marker beacon at or near the glideslope intercept altitude of an ILS approach. It is normally located four to seven miles from the runway threshold on the extended centerline of the runway.

Outside air temperature (OAT): The measured or indicated air temperature (IAT) corrected for compression and friction heating. Also referred to as true air temperature.

Overcontrolling: Using more movement in the control column than is necessary to achieve the desired pitch-and-bank condition.

P

P-factor: A tendency for an aircraft to yaw to the left due to the descending propeller blade on the right producing more thrust than the ascending blade on the left. This occurs when the aircraft's longitudinal axis is in a climbing attitude in relation to the relative wind.

Parasite drag: Drag caused by the friction of air moving over the aircraft structure; its amount varies directly with the airspeed.

Payload (GAMA): The weight of occupants, cargo, and baggage.

Phugoid oscillations: Long-period oscillations of an aircraft around its lateral axis. It is a slow change in pitch accompanied by equally slow changes in airspeed. Angle of attack remains constant, and the pilot often corrects for phugoid oscillations without even being aware of them.

Pilot in command (PIC): The pilot responsible for the operation and safety of an aircraft.

Pilot report (PIREP): Report of meteorological phenomena encountered by aircraft.

Pilot's Operating Handbook/Airplane Flight Manual (POH/AFM): FAA-approved documents published by the airframe manufacturer that list the operating conditions for a particular model of aircraft.

Pitot pressure: Ram air pressure used to measure airspeed.

Pitot-static head: A combination pickup used to sample pitot pressure and static air pressure.

Position error: Error in the indication of the altimeter, ASI, and VSI caused by the air at the static system entrance not being absolutely still.

Positive static stability: The initial tendency of an aircraft to return toward its original condition after it is disturbed.

Powered-lift: A heavier-than-air aircraft capable of vertical takeoff, vertical landing and low-speed flight, that depends mainly on engine-driven lift devices or engine thrust in those regimes and on non-rotating airfoils for lift in horizontal flight (14 CFR 1.1).

Powerplant: A complete engine and propeller combination with accessories.

Precipitation: Any or all forms of water particles (rain, sleet, hail, or snow) that fall from the atmosphere and reach the surface.

Precision approach: A standard instrument approach procedure in which both vertical and horizontal guidance is provided.

Precision approach path indicator (PAPI): A system of lights similar to the VASI, but consisting of one row of lights in two- or four-light systems. A pilot on the correct glideslope will see two white lights and two red lights. See VASI.

Precision approach radar (PAR): A type of radar used at an airport to guide an aircraft through the final stages of landing, providing horizontal and vertical guidance. The radar operator directs the pilot to change heading or adjust the descent rate to keep the aircraft on a path that allows it to touch down at the correct spot on the runway.

Preignition: Ignition occurring in the cylinder before the time of normal ignition. Preignition is often caused by a local hot spot in the combustion chamber igniting the fuel-air mixture.

Pressure altitude: Altitude above the standard 29.92 inches of mercury pressure level. It is read on the altimeter when it is set to 29.92.

Prevailing visibility: The greatest horizontal visibility equaled or exceeded throughout at least half the horizon circle (which is not necessarily continuous).

Preventive maintenance: Simple or minor preservative operations and the replacement of small standard parts not involving complex assembly operation as listed in 14 CFR part 43, appendix A. Certificated pilots may perform preventive maintenance on any aircraft that is owned or operated by them provided that the aircraft is not used in air carrier service.

Primary flight display (PFD): A display that provides increased situational awareness to the pilot by replacing the traditional six instruments used for instrument flight with an easy-to-scan display that provides the horizon, airspeed, altitude, vertical speed, trend, trim, and rate of turn among other key relevant indications.

Procedure turn: A maneuver prescribed when it is necessary to reverse direction to establish an aircraft on the intermediate approach segment or final approach course.

Prohibited area: Designated airspace within which flight of aircraft is prohibited.

Propeller: A device for propelling an aircraft that, when rotated, produces by its action on the air, a thrust approximately perpendicular to its plane of rotation. It includes the control components normally supplied by its manufacturer.

R

Radar: A system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, weather formations, and terrain. The term RADAR was coined in 1941 as an acronym for Radio Detection and Ranging.

Radar approach: The controller provides vectors while monitoring the progress of the flight with radar, guiding the pilot through the descent to the airport/heliport or to a specific runway.

Radar services: Services a controller provides using radar, such as radar vectors, traffic advisories and sequencing.

Radar vector: A heading issued by a controller to give navigational guidance to a radar-identified aircraft.

Radials: The courses oriented from a station.

Radio magnetic indicator (RMI): An electronic navigation instrument that combines a magnetic compass with an ADF or VOR. The card of the RMI acts as a gyro-stabilized magnetic compass, and shows the magnetic heading the aircraft is flying.

Radio or radar altimeter: An electronic altimeter that determines the height of an aircraft above the terrain by measuring the time needed for a pulse of radio-frequency energy to travel from the aircraft to the ground and return.

Read back: A request to repeat a message back to the sender. Pilots also read back clearances to show they understood them.

Receiver autonomous integrity monitoring (RAIM): A system used to verify the usability of the received GPS signals and warns the pilot of any malfunction in the navigation system. This system is required for IFR-certified GPS units.

Reduced vertical separation minimum (RVSM): Reduces the vertical separation between flight levels (FL) 290 and 410 from 2,000 feet to 1,000 feet, and makes six additional FLs available for operation.

Region of reverse command: Flight regime in which flight at a higher airspeed requires a lower power setting and a lower airspeed requires a higher power setting in order to maintain altitude.

Relative bearing (RB): The angular difference between the aircraft heading and the direction to the station, measured clockwise from the nose of the aircraft.

Relative humidity: The ratio of the existing amount of water vapor in the air at a given temperature to the maximum amount that could exist at that temperature; usually expressed in percent.

Relative wind: Direction of the airflow produced by an object moving through the air. The relative wind for an airplane in flight flows in a direction parallel with and opposite to the direction of flight; therefore, the actual flight path of the airplane determines the direction of the relative wind.

Restricted area: Airspace designated under 14 CFR part 73 within which the flight of aircraft, while not wholly prohibited, is subject to restriction.

Rigging: The final adjustment and alignment of an aircraft and its flight control system that provides the proper aerodynamic characteristics.

Rime ice: Rough, milky, opaque ice formed by the instantaneous freezing of small supercooled water droplets.

Risk: The future impact of a hazard that is not eliminated or controlled.

Risk management: The part of the decision-making process which relies on situational awareness, problem recognition, and good judgment to reduce risks associated with each flight.

Roger: I have received all of your last transmission. It does not mean yes or no, so it should not be used to answer a question that needs one of those answers.

Rotorcraft: A heavier-than-air aircraft that depends mainly on the lift generated by one or more rotors for support in flight (14 CFR 1.1).

Rudder: The movable primary control surface mounted on the trailing edge of the vertical fin of an airplane. Movement of the rudder rotates the airplane about its vertical axis.

Ruddervator: A pair of control surfaces on the tail of an aircraft arranged in the form of a V. These surfaces, when moved together by the control wheel, serve as elevators, and when moved differentially by the rudder pedals, serve as a rudder.

Runway centerline lights: Runway lighting which consists of flush centerline lights spaced at 50-foot intervals beginning 75 feet from the landing threshold.

Runway edge lights: A component of the runway lighting system that is used to outline the edges of runways at night or during low visibility conditions. These lights are classified according to the intensity they are capable of producing.

Runway end identifier lights (REIL): A pair of synchronized flashing lights, located laterally on each side of the runway threshold, providing rapid and positive identification of the approach end of a runway.

Runway heading: The magnetic direction that matches the runway centerline extended, not the painted runway number. Pilots are expected to fly that heading without applying drift correction.

S

Say again: A request to repeat all or part of the last transmission.

Sea breeze: A coastal breeze blowing from sea to land caused by the temperature difference when the land surface is warmer than the sea surface. The sea breeze usually occurs during the day and alternates with the land breeze that blows in the opposite direction at night.

Sectional aeronautical charts: Designed for visual navigation of slow- or medium-speed aircraft. Topographic information on these charts features the portrayal of relief, and a judicious selection of visual check points for VFR flight.

Service ceiling: The maximum density altitude where the best rate-of-climb airspeed will produce a 100-feet-per-minute climb at maximum weight while in a clean configuration with maximum continuous power.

Servo tab: An auxiliary control mounted on a primary control surface, which automatically moves in the direction opposite the primary control to provide an aerodynamic assist in the movement of the control.

SIGMET: The acronym for Significant Meteorological information. A weather advisory in abbreviated plain language concerning the occurrence or expected occurrence of potentially hazardous en route weather phenomena that may affect the safety of aircraft operations.

Simplified directional facility (SDF): A NAVAID used for nonprecision instrument approaches. The final approach course is similar to that of an ILS localizer; however, the SDF course may be offset from the runway, generally not more than 3°, and the course may be wider than the localizer, resulting in a lower degree of accuracy.

Single-pilot resource management (SRM): The ability for a pilot to manage all resources effectively to ensure the outcome of the flight is successful.

Situational awareness: Pilot knowledge of where the aircraft is in regard to location, air traffic control, weather, regulations, aircraft status, and other factors that may affect flight.

Skidding turn: An uncoordinated turn in which the rate of turn is too great for the angle of bank, pulling the aircraft to the outside of the turn.

Slipping turn: An uncoordinated turn in which the aircraft is banked too much for the rate of turn, so the horizontal lift component is greater than the centrifugal force, pulling the aircraft toward the inside of the turn.

Small airplane: An airplane of 12,500 pounds or less maximum certificated takeoff weight.

Spatial disorientation: The state of confusion due to misleading information being sent to the brain from various sensory organs, resulting in a lack of awareness of the aircraft position in relation to a specific reference point.

Special flight permit: A flight permit issued to an aircraft that does not meet airworthiness requirements but is capable of safe flight. A special flight permit can be issued to move an aircraft for the purposes of maintenance or repair, buyer delivery, manufacturer flight tests, evacuation from danger, or customer demonstration.

Special use airspace: Airspace in which flight activities are subject to restrictions that can create limitations on the mixed use of airspace. Consists of prohibited, restricted, warning, military operations, and alert areas.

Special VFR: Operations in Class B, C, D and E surface areas in weather below the basic VFR minimums, under an ATC clearance. The pilot must request it and ATC must approve it.

Spin: An aggravated stall that results in an airplane descending in a helical, or corkscrew path.

Spiral instability: A condition that exists when the static directional stability of the airplane is very strong as compared to the effect of its dihedral in maintaining lateral equilibrium.

Spoilers: High-drag devices that can be raised into the air flowing over an airfoil, reducing lift and increasing drag. Spoilers are used for roll control on some aircraft. Deploying spoilers on both wings at the same time allows the aircraft to descend without gaining speed.

Squawk: An ATC instruction to set a code or function on the aircraft transponder, for example "squawk five seven zero seven."

Stabilator: A single-piece horizontal tail surface on an airplane that pivots around a central hinge point. A stabilator serves the purposes of both the horizontal stabilizer and the elevators.

Stability: The inherent quality of an airplane to correct for conditions that may disturb its equilibrium, and to return or to continue on the original flight path. It is primarily an airplane design characteristic.

Stall: A rapid decrease in lift caused by the separation of airflow from the wing's surface, brought on by exceeding the critical angle of attack. A stall can occur at any pitch attitude or airspeed.

Stand by: The controller or pilot must pause for a few seconds, usually to deal with a higher-priority duty. It is not an approval or a denial.

Standard atmosphere: At sea level, the standard atmosphere consists of a barometric pressure of 29.92 inches of mercury (inHg) or 1013.2 millibars, and a temperature of 15 °C (59 °F). Pressure and temperature normally decrease as altitude increases.

Standard empty weight (GAMA): This weight consists of the airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the airplane including fixed ballast, hydraulic fluid, unusable fuel, and full engine oil.

Standard holding pattern: A holding pattern in which all turns are made to the right.

Standard instrument departure procedures (SIDS): Published procedures to expedite clearance delivery and to facilitate transition between takeoff and en route operations.

Standard rate turn: A turn at 3 degrees per second, which is 360 degrees in 2 minutes, for low- and medium-speed aircraft. For high-speed aircraft it is 1.5 degrees per second, or 360 degrees in 4 minutes.

Standard terminal arrival route (STAR): A preplanned IFR ATC arrival procedure published for pilot use in graphic and/or textual form.

Static pressure: Pressure of air that is still or not moving, measured perpendicular to the surface of the aircraft.

Static stability: The initial tendency an aircraft displays when disturbed from a state of equilibrium.

Station: A location in the airplane that is identified by a number designating its distance in inches from the datum. The datum is, therefore, identified as station zero. An item located at station +50 would have an arm of 50 inches.

Stationary front: A front that is moving at a speed of less than 5 knots.

Steep turns: In instrument flight, any turn greater than standard rate; in visual flight, anything greater than a 45° bank.

Sterile flight deck: The rule that flight crews of airlines may not do non-essential duties or activities during critical phases of flight (14 CFR 121.542).

Stop-and-go: A procedure in which an aircraft lands, makes a complete stop on the runway and then takes off again from that point.

Structural icing: The accumulation of ice on the exterior of the aircraft.

Supercharger: An engine- or exhaust-driven air compressor used to provide additional pressure to the induction air so the engine can produce additional power.

Supercooled water droplets: Water droplets that have been cooled below the freezing point, but are still in a liquid state.

Surface analysis chart: A report that depicts an analysis of the current surface weather. Shows the areas of high and low pressure, fronts, temperatures, dewpoints, wind directions and speeds, local weather, and visual obstructions.

Synthetic vision: A realistic display depiction of the aircraft in relation to terrain and flight path.

T

T-tail: An aircraft with the horizontal stabilizer mounted on the top of the vertical stabilizer, forming a T.

Takeoff decision speed (V1): The calibrated airspeed on the ground at which the pilot is assumed to have decided to continue or discontinue the takeoff after an engine failure or other problem.

Takeoff safety speed (V2): A referenced airspeed obtained after liftoff at which the required one-engine-inoperative climb performance can be achieved.

Taxiway lights: Omnidirectional lights that outline the edges of the taxiway and are blue in color.

Temporary flight restriction (TFR): A restriction on flight in a defined area, published by NOTAM, imposed for reasons such as protecting people and property, disaster relief or special events.

Terminal aerodrome forecast (TAF): A report established for the 5 statute mile radius around an airport. Utilizes the same descriptors and abbreviations as the METAR report.

Terminal arrival area (TAA): A procedure to provide a new transition method for arriving aircraft equipped with FMS and/or GPS navigational equipment. The TAA contains a "T" structure that normally provides a NoPT for aircraft using the approach.

Terminal radar service areas (TRSA): Areas where participating pilots can receive additional radar services. The purpose of the service is to provide separation between all IFR operations and participating VFR aircraft.

Terrain awareness and warning system (TAWS): A system that uses GPS position and a database of terrain and obstructions to warn the pilot of terrain and obstacles ahead.

The leans: A physical sensation caused by an abrupt correction of a banked attitude entered too slowly to stimulate the motion sensing system in the inner ear. The abrupt correction can create the illusion of banking in the opposite direction.

Thrust: The forward force produced by the powerplant, propeller or jet engine. It opposes or overcomes drag.

Thrust line: An imaginary line passing through the center of the propeller hub, perpendicular to the plane of the propeller rotation.

Torque: (1) A resistance to turning or twisting. (2) Forces that produce a twisting or rotating motion. (3) In an airplane, the tendency of the aircraft to turn (roll) in the opposite direction of rotation of the engine and propeller. (4) In helicopters with a single, main rotor system, the tendency of the helicopter to turn in the opposite direction of the main rotor rotation.

Touch-and-go: A landing followed immediately by a takeoff, without stopping or leaving the runway.

Touchdown zone elevation (TDZE): The highest elevation in the first 3,000 feet of the landing surface, TDZE is indicated on the instrument approach procedure chart when straight-in landing minimums are authorized.

Touchdown zone lights: Two rows of transverse light bars disposed symmetrically about the runway centerline in the runway touchdown zone.

Track: The actual path made over the ground in flight.

Tracking: Flying a heading that will maintain the desired track to or from the station regardless of crosswind conditions.

Traffic Alert Collision Avoidance System (TCAS): An airborne system developed by the FAA that operates independently from the ground-based Air Traffic Control system. Designed to increase flight deck awareness of proximate aircraft and to serve as a "last line of defense" for the prevention of midair collisions.

Traffic pattern: The standard flow of aircraft around an airport, made up of the upwind, crosswind, downwind, base and final legs.

Trailing edge: The portion of the airfoil where the airflow over the upper surface rejoins the lower surface airflow.

Transponder: The airborne portion of the ATC radar beacon system.

Transponder code: One of 4,096 four-digit discrete codes ATC assigns to distinguish between aircraft.

Tricycle gear: Landing gear employing a third wheel located on the nose of the aircraft.

Trim: To adjust the aerodynamic forces on the control surfaces so that the aircraft maintains the set attitude without any control input.

Trim tab: A small auxiliary hinged portion of a movable control surface that can be adjusted during flight to a position resulting in a balance of control forces.

Tropopause: The boundary layer between the troposphere and the stratosphere which acts as a lid to confine most of the water vapor, and the associated weather, to the troposphere.

Troposphere: The layer of the atmosphere extending from the surface to a height of 20,000 to 60,000 feet, depending on latitude.

True airspeed: Actual airspeed, determined by applying a correction for pressure altitude and temperature to the CAS.

True altitude: The vertical distance of the airplane above sea level--the actual altitude. It is often expressed as feet above mean sea level (MSL). Airport, terrain, and obstacle elevations on aeronautical charts are true altitudes.

Turbine engine: An aircraft engine which consists of an air compressor, a combustion section, and a turbine. Thrust is produced by increasing the velocity of the air flowing through the engine.

Turbocharger: An air compressor driven by exhaust gases, which increases the pressure of the air going into the engine through the carburetor or fuel injection system.

Turbofan engine: A fanlike turbojet engine designed to create additional thrust by diverting a secondary airflow around the combustion chamber.

Turbojet engine: A turbine engine that produces thrust by increasing the velocity of the air flowing through the engine.

Turboprop engine: A turbine engine which drives a propeller through a reduction gearing arrangement. Most of the energy in the exhaust gases is converted into torque, rather than using its acceleration to drive the aircraft.

Turboshaft engine: A gas turbine engine that delivers power through a shaft to operate something other than a propeller.

Turn coordinator: A rate gyro that senses both roll and yaw due to the gimbal being canted. Has largely replaced the turn-and-slip indicator in modern aircraft.

Turn-and-slip indicator: A flight instrument consisting of a rate gyro to indicate the rate of yaw and a curved glass inclinometer to indicate the relationship between gravity and centrifugal force. The turn-and-slip indicator indicates the relationship between angle of bank and rate of yaw. Also called a turn-and-bank indicator.

Type rating: A rating required to act as pilot in command of a large aircraft over 12,500 pounds maximum certificated takeoff weight, a turbojet-powered airplane or a powered-lift aircraft (14 CFR 61.31).

U

Unable: Indicates inability to comply with a specific instruction, request or clearance.

Uncontrolled airspace: Class G airspace that has not been designated as Class A, B, C, D, or E. It is airspace in which air traffic control has no authority or responsibility to control air traffic; however, pilots should remember there are VFR minimums which apply to this airspace.

UNICOM: A nongovernment communication facility that may provide airport information at certain airports. Automated UNICOM systems provide weather and radio check, selectable by microphone clicks.

Upwind leg: A flight path that begins after departure and continues straight ahead along the extended runway centerline.

Urgency: A condition of being concerned about safety and of requiring timely but not immediate assistance. It is a potential distress condition.

Useful load: The weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil. It is the basic empty weight subtracted from the maximum allowable gross weight. This term applies to general aviation aircraft only.

V

V-G diagram: A chart that relates velocity to load factor. It is valid only for a specific weight, configuration and altitude and shows the maximum amount of positive or negative lift the airplane is capable of generating at a given speed.

V-tail: A design which utilizes two slanted tail surfaces to perform the same functions as the surfaces of a conventional elevator and rudder configuration. The fixed surfaces act as both horizontal and vertical stabilizers.

Vapor lock: A problem that mostly affects gasoline-fuelled internal combustion engines. It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system.

Variation: Compass error caused by the difference in the physical locations of the magnetic north pole and the geographic north pole.

Vector (force): A graphic representation of a force that shows both its magnitude and direction.

Velocity: The speed or rate of movement in a certain direction.

Venturi tube: A specially shaped tube attached to the outside of an aircraft to produce suction to allow proper operation of gyro instruments.

Verify: A request to confirm information, for example "verify assigned altitude."

Vertical axis: An imaginary line passing vertically through the center of gravity of an aircraft. The vertical axis is called the z-axis or the yaw axis.

Vertical speed indicator (VSI): A rate-of-pressure change instrument that gives an indication of any deviation from a constant pressure level.

Very-high frequency omnidirectional range (VOR): Electronic navigation equipment in which the flight deck instrument identifies the radial or line from the VOR station, measured in degrees clockwise from magnetic north, along which the aircraft is located.

VFE: The maximum speed with the flaps extended. The upper limit of the white arc.

VFR on top: ATC authorization for an IFR aircraft to operate in VFR conditions at any appropriate VFR altitude.

VFR terminal area chart: At a scale of 1:250,000, a chart that depicts Class B airspace, which provides for the control or segregation of all the aircraft within the Class B airspace.

Victor airways: Airways based on a centerline that extends from one VOR or VORTAC navigation aid or intersection, to another navigation aid (or through several navigation aids or intersections); used to establish a known route for en route procedures between terminal areas.

Visual approach: An approach on an IFR flight plan that lets the pilot proceed visually and clear of clouds to the airport. The pilot must have the airport or the preceding aircraft in sight, and the weather must be a ceiling of at least 1,000 feet and visibility of at least 3 miles.

Visual approach slope indicator (VASI): A visual aid of lights arranged to provide descent guidance information during the approach to the runway. A pilot on the correct glideslope will see red lights over white lights.

Visual descent point (VDP): A defined point on the final approach course of a nonprecision straight-in approach procedure from which normal descent from the MDA to the runway touchdown point may be commenced, provided the runway environment is clearly visible to the pilot.

Visual flight rules (VFR): Flight rules adopted by the FAA governing aircraft flight using visual references. VFR operations specify the amount of ceiling and the visibility the pilot must have in order to operate according to these rules.

Visual meteorological conditions (VMC): Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling meeting or exceeding the minimums specified for VFR.

VLE: Landing gear extended speed. The maximum speed at which an airplane can be safely flown with the landing gear extended.

VLO: Landing gear operating speed. The maximum speed for extending or retracting the landing gear if using an airplane equipped with retractable landing gear.

VNE: The never-exceed speed. Operating above this speed is prohibited since it may result in damage or structural failure. The red line on the airspeed indicator.

VNO: The maximum structural cruising speed. Do not exceed this speed except in smooth air. The upper limit of the green arc.

VOR test facility (VOT): A ground facility which emits a test signal to check VOR receiver accuracy. Some VOTs are available to the user while airborne, while others are limited to ground use only.

VORTAC: A facility consisting of two components, VOR and TACAN, which provides three individual services: VOR azimuth, TACAN azimuth, and TACAN distance (DME) at one site.

VS0: The stalling speed or the minimum steady flight speed in the landing configuration. In small airplanes, this is the power-off stall speed at the maximum landing weight in the landing configuration (gear and flaps down). The lower limit of the white arc.

VS1: The stalling speed or the minimum steady flight speed obtained in a specified configuration. For most airplanes, this is the power-off stall speed at the maximum takeoff weight in the clean configuration (gear up, if retractable, and flaps up). The lower limit of the green arc.

VX: Best angle-of-climb speed. The airspeed at which an airplane gains the greatest amount of altitude in a given distance. It is used during a short-field takeoff to clear an obstacle.

VY: Best rate-of-climb speed. This airspeed provides the most altitude gain in a given period of time.

VYSE: Best rate-of-climb speed with one engine inoperative. This airspeed provides the most altitude gain in a given period of time in a light, twin-engine airplane following an engine failure.

W

Wake turbulence: Wingtip vortices that are created when an airplane generates lift. When an airplane generates lift, air spills over the wingtips from the high pressure areas below the wings to the low pressure areas above them. This flow causes rapidly rotating whirlpools of air called wingtip vortices or wake turbulence.

Warm front: The boundary area formed when a warm air mass contacts and flows over a colder air mass. Warm fronts cause low ceilings and rain.

Warning area: An area containing hazards to any aircraft not participating in the activities being conducted in the area. Warning areas may contain intensive military training, gunnery exercises, or special weapons testing.

Waypoint: A designated geographical location used for route definition or progress-reporting purposes and is defined in terms of latitude/longitude coordinates.

Weather depiction chart: Details surface conditions as derived from METAR and other surface observations.

Weight: The force exerted by an aircraft from the pull of gravity.

Wide area augmentation system (WAAS): A differential global positioning system (DGPS) that improves the accuracy of the system by determining position error from the GPS satellites, then transmitting the error, or corrective factors, to the airborne GPS receiver.

Wilco: I have received your message, understand it and will comply with it.

Wind correction angle (WCA): The angle between the desired track and the heading of the aircraft necessary to keep the aircraft tracking over the desired track.

Wind direction indicators: Indicators that include a wind sock, wind tee, or tetrahedron. Visual reference will determine wind direction and runway in use.

Wind shear: A sudden, drastic shift in windspeed, direction, or both that may occur in the horizontal or vertical plane.

Winds and temperature aloft forecast (FB): A twice daily forecast that provides wind and temperature forecasts for specific locations in the contiguous United States.

Wing area: The total surface of the wing (in square feet), which includes control surfaces and may include wing area covered by the fuselage (main body of the airplane), and engine nacelles.

Wing span: The maximum distance from wingtip to wingtip.

Wings: Airfoils attached to each side of the fuselage and are the main lifting surfaces that support the airplane in flight.

Wingtip vortices: The rapidly rotating air that spills over an airplane's wings during flight. The intensity of the turbulence depends on the airplane's weight, speed, and configuration. Also referred to as wake turbulence. Vortices from heavy aircraft may be extremely hazardous to small aircraft.

World Aeronautical Charts (WAC): A standard series of aeronautical charts covering land areas of the world at a size and scale convenient for navigation (1:1,000,000) by moderate speed aircraft. Topographic information includes cities and towns, principal roads, railroads, distinctive landmarks, drainage, and relief.

Z

Zulu time: A term used in aviation for coordinated universal time (UTC) which places the entire world on one time standard.

If we are missing a term you expected to find, let us know here.

Sources

FAA. Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Glossary. https://www.faa.gov/sites/faa.gov/files/21_phak_glossary.pdf
FAA. Pilot/Controller Glossary. https://www.faa.gov/air_traffic/publications/atpubs/pcg_html/index.html
FAA. Aeronautical Information Manual, Chapter 4, Section 3: Airport Operations (traffic pattern legs). https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap4_section_3.html
Electronic Code of Federal Regulations. 14 CFR 1.1, General definitions. https://www.ecfr.gov/current/title-14/section-1.1
Electronic Code of Federal Regulations. 14 CFR 22.100, Light-sport category eligibility. https://www.ecfr.gov/current/title-14/section-22.100
Electronic Code of Federal Regulations. 14 CFR 61.31 and 61.56, Type rating requirements and flight review. https://www.ecfr.gov/current/title-14/section-61.56
Electronic Code of Federal Regulations. 14 CFR 91.207, Emergency locator transmitters. https://www.ecfr.gov/current/title-14/section-91.207
Electronic Code of Federal Regulations. 14 CFR 121.542, Flight crewmember duties. https://www.ecfr.gov/current/title-14/section-121.542

Frequently Asked Questions

Where do these definitions come from?

Most come from the FAA's Pilot's Handbook of Aeronautical Knowledge glossary and the FAA Pilot/Controller Glossary, adapted for length. A few are drawn from 14 CFR and the Aeronautical Information Manual.

What does Roger mean in aviation?

In radio use it means "I have received all of your last transmission." It does not mean yes or no.

What does Wilco mean?

It means "I have received your message, understand it and will comply with it."

What does Mayday mean?

It is the international radiotelephony distress signal. Repeated three times, it indicates imminent and grave danger and that immediate assistance is requested.

What is Zulu time?

Zulu time is the aviation name for coordinated universal time (UTC), which puts the entire world on one time standard.

Keep PilotPassion in your Google results

Add us as a preferred source and we are more likely to appear in your Top Stories.

Aviation Terminology & Jargon

Aviation Glossary

#

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

R

S

T

U

V

W

Z

Sources

Frequently Asked Questions

Where do these definitions come from?

What does Roger mean in aviation?

What does Wilco mean?

What does Mayday mean?

What is Zulu time?

Read Next

How Much Does An Aeronca Champ Cost? (2026 Market Price)

How Much Does A Beechcraft G36 Bonanza Cost?

How Much Does A Cessna 150 Cost?