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.  G-2