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 controller’s radar scope. 

Air route surveillance radar (ARSR). Air route traffic control center (ARTCC) radar used primarily to detect and display an aircraft’s 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 craft’s 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. 

ALS.  See approach lighting system. 

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. 

AME. See 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. 

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. 

ARSR.  See air route surveillance radar. 

ARTCC.  See air route traffic control center. 

