## 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. 

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. 

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) 

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. 

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. 

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. 

Automated flight service station (AFSS). An air traffic facility that provides pilot briefings and numerous other services. 

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. 

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. 

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. 

