articulated rotor (helicopter rotor). A helicopter rotor in which each blade is connected to the rotor hub in such a way that it is free to move up and down (flap), move back and forth in its plane of rotation (drag), and change its pitch angle (feather).
artificial aging. A method of aluminum alloy heat treatment in which the part is heated and quenched (solution heat-treated) and then held at a specified elevated temperature for a period of time.
The metal gains additional strength by this process. Artificial aging is also called precipitation heat treatment.
artificial antenna (radio antenna). A device attached to the output of a radio transmitter to use when adjusting its output. The artificial antenna, also called a dummy load, has the same impedance as the antenna, but the radio signal put into the artificial antenna is not radiated.
artificial feel (aircraft control system). A type of force feedback used in the automatic flight control systems of some aircraft. Artificial feel produces an opposition to the pilot’s movement of the controls that is proportional to the aerodynamic loads acting on the control surfaces.
artificial horizon. A flight instrument that provides the pilot with a visual reference when the natural horizon is not visible. A bar or display, held in a constant relationship with the earth’s horizon by a gyro, serves as the reference.
ARTS (automated radar terminal systems). A term used to define several automated air traffic control systems:
 ARTS II. An automated, nontracking radar system with capability for air traffic control at terminals with low to medium activity.
 ARTS III. A beacon-tracking automated radar system used in medium- to high-activity terminals. ARTS III detects, tracks, and predicts secondary radar-derived aircraft targets.
 ARTS IIIA. A radar-tracking and beacon-tracking automated radar system that tracks and predicts primary as well as secondary radar-derived aircraft targets.
asbestos. A fiber of magnesium silicate that is highly resistant to fire and has good insulating qualities.
A-scan (radarscope). A type of radar display in which the time base (distance or range) is displayed on a horizontal line and the target appears as a vertical displacement along the time base.
ASD (aircraft situation display) (air traffic control). A computer system that receives radar track data from all 20 Continental U.S. air route traffic control centers, organizes this data into a mosaic display, and presents it on a computer screen.
The ASD provides the traffic management coordinator with multiple methods of selection and highlighting of individual aircraft or groups of aircraft. The user has the option of superimposing these aircraft positions over any number of background displays, which include ARTCC boundaries, any stratum of en route sector boundaries, fixes, airways, military and other special-use airspace, airports, and geopolitical boundaries.