Glossary Abort.  To terminate an operation prematurely when it is seen  that the desired result will not occur. Advection. In weather, the term used for the horizontal  transport of heat by the wind.  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.  Aeronautics.  The branch of science that deals with flight  and with the operations of all types of aircraft. Aerostat.  A device supported in the air by displacing more  than its own weight of air. Absolute altitude.  The actual distance between an aircraft  and the terrain over which it is flying. Advisory circular (AC).  An FAA publication that informs  the aviation public, in a systematic way, of nonregulatory  material. Automated flight service station (AFSS). An air traffic  facility that provides pilot briefings and numerous other  services. Accident.  An occurrence associated with the operation of an  aircraft which takes place between the time any person boards  the aircraft with the intention of flight and all such persons  have disembarked, and in which any person suffers death or  serious injury, or in which the aircraft receives substantial  damage. (NTSB 830.2) AGL.  Above ground level. Aircraft.  A device that is used or intended to be used for  flight in the air. Airport.  An area of land or water that is used for the landing  and takeoff of an aircraft. Aeronautical Information Manual (AIM). A reference  publication for pilots. Airworthiness directive (AD).  A regulatory notice sent out  by the FAA to the registered owner of an aircraft informing  him or her of a condition that prevents the aircraft from  meeting its conditions for airworthiness. Compliance  requirements will be stated in the AD. Altimeter.  A pressure reading device that, when properly  calibrated, indicates the height of the aircraft above mean  sea level (MSL). An altimeter is a required instrument in  a balloon, as directed by 14 CFR Part 31, Airworthiness  Standards: Manned Free Balloons. Adiabatic process.  In weather, the change of the temperature  of air without transferring heat. In the adiabatic process,  compression of the air mass results in the warming of the air;  conversely, the expansion of the air mass results in cooling  of the air.  Administrator. The FAA Administrator or any person  to whom he or she has delegated authority in the matter  concerned. Aeronaut.  A person who operates or travels in a balloon  or airship. Altimeter setting.  The station pressure (barometric pressure  at the location the reading is taken) which has been corrected  for the height of the station above sea level. Ambient air. Air surrounding the outside of a balloon  envelope. Anabatic winds.  In weather, a wind that blows up the slope  of a hill or mountain due to increased heating along the  valley walls.  G-1