Aeronautical Terms beginning with A
Absolute accuracy
The ability to determine present position in space independently, and is most often used by pilots.
Absolute altitude
The actual distance between an aircraft and the terrain over which it is flying.
Absolute pressure
Pressure measured from the reference of zero pressure, or a vacuum.
Acceleration error
A magnetic compass error apparent when the aircraft accelerates while flying on an easterly or westerly heading, causing the compass card to rotate toward North.
Accelerometer
A part of an inertial navigation system (INS) that accurately measures the force of acceleration in one direction.
Adverse yaw
A flight condition at the beginning of a turn in which the nose of the aircraft starts to move in the direction opposite the direction the turn is being made, caused by the induced drag produced by the downward-deflected aileron holding back the wing as it begins to rise.
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.
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.
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.
Air data computer (ADC)
An aircraft computer that receives and processes pitot pressure, static pressure, and temperature to calculate very precise altitude, indicated airspeed, true airspeed, and air temperature.
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/Facility Directory (A/FD)
An FAA publication containing information on all airports, communications, and NAVAIDs. Title changed to Chart Supplement.
Airport surface detection equipment (ASDE)
Radar equipment specifically designed to detect all principal features and traffic on the surface of an airport, presenting the entire image on the control tower console; used to augment visual observation by tower personnel of aircraft and/or vehicular movements on runways and taxiways.
Airport surveillance radar (ASR)
Approach control radar used to detect and display an aircrafts position in the terminal area.
Airport surveillance radar approach
An instrument approach in which ATC issues instructions for pilot compliance based on aircraft position in relation to the final approach course and the distance from the end of the runway as displayed on the controllers radar scope.
Air route surveillance radar (ARSR)
Air route traffic control center (ARTCC) radar used primarily to detect and display an aircrafts position while en route between terminal areas.
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.
Airspeed indicator
A differential pressure gauge that measures the dynamic pressure of the air through which the aircraft is flying. Displays the crafts airspeed, typically in knots, to the pilot.
Air traffic control radar beacon system (ATCRBS).
Sometimes called secondary surveillance radar (SSR), which utilizes a transponder in the aircraft. The ground equipment is an interrogating unit, in which the beacon antenna is mounted so it rotates with the surveillance antenna. The interrogating unit transmits a coded pulse sequence that actuates the aircraft transponder. The transponder answers the coded sequence by transmitting a preselected coded sequence back to the ground equipment, providing a strong return signal and positive aircraft identification, as well as other special data.
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.
Alert area
An area in which there is a high volume of pilot training or an unusual type of aeronautical activity.
Almanac data
Information the global positioning system (GPS) receiver can obtain from one satellite which describes the approximate orbital positioning of all satellites in the constellation. This information is necessary for the GPS receiver to know what satellites to look for in the sky at a given time.
Alternate airport
An airport designated in an IFR flight plan, providing a suitable destination if a landing at the intended airport becomes inadvisable.
Alternate static source valve
A valve in the instrument static air system that supplies reference air pressure to the altimeter, airspeed indicator, and vertical speed indicator if the normal static pickup should become clogged or iced over.
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.
Amendment status
The circulation date and revision number of an instrument approach procedure, printed above the procedure identification.
Ammeter
An instrument installed in series with an electrical load used to measure the amount of current flowing through the load.
Aneroid
The sensitive component in an altimeter or barometer that measures the absolute pressure of the air. It is a sealed, flat capsule made of thin disks of corrugated metal soldered together and evacuated by pumping all of the air out of it.
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 acute angle formed between the chord line of an airfoil and the direction of the air striking the airfoil.
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 glide path information for safe transition from instrument to visual flight.
Area chart
Part of the low-altitude en route chart series, this chart furnishes terminal data at a larger scale for congested areas.
Area navigation (RNAV)
Allows a pilot to fly a selected course to a predetermined point without the need to overfly ground-based navigation facilities, by using waypoints.
Atmospheric propagation delay
A bending of the electromagnetic (EM) wave from the satellite that creates an error in the GPS system.
Attitude and heading reference systems (AHRS)
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 director indicator (ADI)
An aircraft attitude indicator that incorporates flight command bars to provide pitch and roll commands.
Attitude indicator
The foundation for all instrument flight, this instrument reflects the airplanes attitude in relation to the horizon.
Attitude instrument flying
Controlling the aircraft by reference to the instruments rather than by outside visual cues.
Autokinesis
Nighttime visual illusion that a stationary light is moving, which becomes apparent after several seconds of staring at the light.
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.
Automated Surface Observing Station (ASOS)
Weather reporting system which provides surface observations every minute via digitized voice broadcasts and printed reports.
Automatic dependent surveillance broadcast (ADS-B)
A device used in aircraft that repeatedly broadcasts a message that includes position (such as latitude, longitude, and altitude), velocity, and possibly 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.
Aviation medical examiner (AME)
A physician with training in aviation medicine designated by the Civil Aerospace Medical Institute (CAMI).
Azimuth card
A card that may be set, gyroscopically controlled, or driven by a remote compass.
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