Aeronautical Terms beginning with A
A-RNAV
Advanced Area Navigation
A.C.
Alternating Current.
A/FD
Airport/Facility Directory—obsolete. Changed to Chart Supplement.
Abbreviated IFR Flight Plans
An authorization by ATC requiring pilots to submit only that information needed for the purpose of ATC. It includes only a small portion of the usual IFR flight plan information. In certain instances, this may be only aircraft identification, location, and pilot request. Other information may be requested if needed by ATC for separation/control purposes. It is frequently used by aircraft which are airborne and desire an instrument approach or by aircraft which are on the ground and desire a climb to VFR-on-top.
Abeam Fix
A fix, NAVAID, point, or object positioned approximately 90 degrees to the right or left of the aircraft track along a route of flight. Abeam indicates a general position rather than a precise point.
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.
AC
Advisory Circular
ACAS
Airborne Collision Avoidance System
Accelerate-Stop Distance Available (ASDA)
The runway plus stopway length declared available and suitable for the acceleration and deceleration of an airplane aborting a takeoff.
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.
ADF
Automatic Direction Finder.
ADI
Attitude Director Indicator.
ADM
Aeronautical Decision-Making.
ADS
Automatic Dependent Surveillance
ADSB
Automatic Dependent Surveillance Broadcast.
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.
AER
Approach End of Runway
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.
AFM
Airplane Flight Manual or Aircraft Flight Manual
AFSS
Automated Flight Service Station
AGL
Above Ground Level
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.
AIM
Aeronautical Information Manual
AIP
Aeronautical Information Publication
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.
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)
A facility established to provide air traffic control service to aircraft operating on IFR flight plans within controlled airspace and principally during the en route phase of flight
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.
Air Traffic Service (ATS)
Air traffic service is an ICAO generic term meaning variously, flight information service, alerting service, air traffic advisory service, air traffic control service (area control service, approach control service, or aerodrome control service).
Air Traffic Service (ATS) route
A specified route designated for channeling the flow of traffic as necessary for the provision of air traffic services. The term “ATS route” refers to a variety of airways, including jet routes, area navigation (RNAV) routes, and arrival and departure routes. An ATS route is defined by route specifications, which may include:
(1) An ATS route designator;
(2) The path to or from significant points;
(3) Distance between significant points;
(4) Reporting requirements; and
(5) The lowest safe altitude determined by the appropriate authority.
Aircraft Approach Category
A grouping of aircraft based on a speed of 1.3 times the stall speed in the landing configuration at maximum gross landing weight. An aircraft must fit in only one category. If it is necessary to maneuver at speeds in excess of the upper limit of a speed range for a category, the minimums for the category for that speed must be used. For example, an aircraft which falls in Category A, but is circling to land at a speed in excess of 91 knots, must use the approach Category B minimums when circling to land. The categories are A-E.
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.
Airport Diagram
A full-page depiction of the airport that includes the same features of the airport sketch plus additional details such as taxiway identifiers, airport latitude and longitude, and building identification. Airport diagrams are located in the U.S. Terminal Procedures booklet following the instrument approach charts for a particular airport.
Airport Sketch
Depicts the runways and their length, width, and slope, the touchdown zone elevation, the lighting system installed on the end of the runway, and taxiways. Airport sketches are located on the lower left or right portion of the instrument approach chart.
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.
Airport/Facility Directory (A/FD)
Regional booklets published by the National Aeronautical Charting Office. Title changed to Chart Supplement. (NACO) that provide textual information about all airports, both VFR and IFR. The A/FD includes runway length and width, runway surface, load bearing capacity, runway slope, airport services, and hazards such as birds and reduced visibility.
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.
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.
AIS
Airmen’s Information System
ALAR
Approach and Landing Accident Reduction
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.
ALS
Approach Lighting System.
ALSF-1
Approach Light System With Sequenced Flashing Lights In ILS CAT-I Configuration
ALSF-2
Approach Light System With Sequenced Flashing Lights In ILS Cat-II Configuration. The ALSF-2 May Operate As An SSALR When Weather Conditions Permit
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
An instrument which determines the altitude of an object with respect to a fixed level. A pressure altimeter.
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.
AMASS
Airport Movement Area Safety System
AME
Aviation Medical Examiner.
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.
ANP
Actual Navigation Performance
ANR
Advanced Navigation Route
Anti-ice
Preventing the accumulation of ice on an aircraft structure via a system designed for that purpose.
AOA
Airport Operating Area
AP
Autopilot System
Approach Clearance
Authorization by ATC for a pilot to conduct an instrument approach. The type of instrument approach for which a clearance and other pertinent information is provided in the approach clearance when required.
Approach End of Runway (AER)
The first portion of the runway available for landing. If the runway threshold is displaced, use the displaced threshold latitude/longitude as the AER.
Approach Fix
From a database coding standpoint, an approach fix is considered to be an identifiable point in space from the intermediate fix (IF) inbound. A fix located between the initial approach fix (IAF) and the IF is considered to be associated with the approach transition or feeder route.
Approach Gate
An imaginary point used by ATC to vector aircraft to the final approach course. The approach gate is established along the final approach course 1 NM from the final approach fix (FAF) on the side away from the airport and is located no closer than 5 NM from the landing threshold.
Approach Light System (ALS)
An airport lighting facility which provides visual guidance to landing aircraft by radiating light beams in a directional pattern by which the pilot aligns the aircraft with the extended centerline of the runway on his/her final approach for landing. Condenser-Discharge Sequential Flashing Lights/Sequenced Flashing Lights may be installed in conjunction with the ALS at some airports. Types of Approach Light Systems are: ALSF-1, ALSF-2, SSALF, SSALR, MALSF, MALSR, LDIN, RAIL, ODALS.
Appropriate Obstacle Clearance Minimum Altitude
Any of the following: Minimum En Route IFR Altitude, Minimum IFR Altitude, Minimum Obstruction Clearance Altitude, Minimum Vectoring Altitude.
Appropriate Terrain Clearance Minimum Altitude
Any of the following: Minimum En Route IFR Altitude, Minimum IFR Altitude, Minimum Obstruction Clearance Altitude, Minimum Vectoring Altitude.
APV
Approach With Vertical Guidance
Arc
The track over the ground of an aircraft flying at a constant distance from a navigational aid by reference to distance measuring equipment (DME).
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.
ARSR
Air Route Surveillance Radar.
ARTCC
Air Route Traffic Control Center.
ARTS
Automated Radar Terminal System
ASDA
Accelerate-Stop Distance Available
ASDAR
Aircraft To Satellite Data Relay
ASDE
Airport Surface Detection Equipment.
ASDE-3
Airport Surface Detection Equipment-3
ASDE-X
Airport Surface Detection Equipment-X
ASOS
Automated Surface Observing Station.
ASR
Airport Surveillance Radar.
ATC
Air Traffic Control.
ATC-TFM
Air Traffic Control Traffic Flow Management
ATCRBS
Air Traffic Control Radar Beacon System.
ATCSCC
Air Traffic Control System Command Center
ATCT
Airport Traffic Control Tower
ATD
Along-Track Distance
ATIS
Automatic Terminal Information Service.
ATM
Air Traffic Management
Atmospheric propagation delay
A bending of the electromagnetic (EM) wave from the satellite that creates an error in the GPS system.
ATS
Air Traffic Service
ATT
Attitude Retention 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.
Autoland Approach
An autoland approach is a precision instrument approach to touchdown and, in some cases, through the landing rollout. An autoland approach is performed by the aircraft autopilot which is receiving position information and/or steering commands from onboard navigation equipment. Note: Autoland and coupled approaches are flown in VFR and IFR. It is common for carriers to require their crews to fly coupled approaches and autoland approaches (if certified) when the weather conditions are less than approximately 4,000 RVR.
Automated Surface Observing Station (ASOS)
Weather reporting system which provides surface observations every minute via digitized voice broadcasts and printed reports.
Automated Surface Observing System (ASOS)/Automated Weather Sens
The ASOS/AWSS is the primary surface weather observing system of the U.S.
Automated Weather Observing System (AWOS)
A suite of sensors which measure, collect, and disseminate weather data. AWOS stations provide a minute-by minute update of weather parameters such as wind speed and direction, temperature and dew point, visibility, cloud heights and types, precipitation, and barometric pressure. A variety of AWOS system types are available (from AWOS 1 to AWOS 3), each of which includes a different sensor array.
Automated Weather Sensor System (AWSS)
The AWSS is part of the Aviation Surface Weather Observation Network suite of programs and provides pilots and other users with weather information through the Automated Surface Observing System. The AWSS sensor suite automatically collects, measures, processes, and broadcasts surface weather data.
Automated Weather System
Any of the automated weather sensor platforms that collect weather data at airports and disseminate the weather information via radio and/or landline. The systems currently consist of the Automated Surface Observing System (ASOS), Automated Weather Sensor System (AWSS) and Automated Weather Observation System (AWOS).
Automatic Dependent Surveillance-Broadcast (ADS-B)
A surveillance system that continuously broadcasts GPS position information, aircraft identification, altitude, velocity vector, and direction to all other aircraft and air traffic control facilities within a specific area. Automatic dependent surveillance-broadcast (ADS-B) information will be displayed in the cockpit via a cockpit display of traffic information (CDTI) unit, providing the pilot with greater situational awareness. ADS-B transmissions will also provide controllers with a more complete picture of traffic and will update that information more frequently than other surveillance equipment.
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)
A recorded broadcast available at most airports with an operating control tower that includes crucial information about runways and instrument approaches in use, specific outages, and current weather conditions, including visibility.
Aviation medical examiner (AME)
A physician with training in aviation medicine designated by the Civil Aerospace Medical Institute (CAMI).
AVN
Office of Aviation System Standards
AWOS
Automated Weather Observing System.
AWSS
Automated Weather Sensor System
Azimuth card
A card that may be set, gyroscopically controlled, or driven by a remote compass.
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