Originally Posted by The Manual
Thrust Recoveries for Engine Failure During Takeoff
In takeoff mode, two separate systems attempt to provide maximum available
thrust when the performance of one engine significantly differs from the
other. These systems are automatic reserve thrust (ART) and automatic
thrust restoration (ATR).
Automatic Reserve Thrust (ART) System
The ART system combines features of the digital flight guidance computer
(DFGC) and the JT8D-200 fuel control to provide maximum rated thrust in
the event of an engine failure during a normal thrust takeoff. Upon actuation
of the ART system, thrust is increased without throttle movement by the
opening of a solenoid-operated fuel valve in the engine fuel controls of both
engines.
The ART system is READY when the airplane is on the ground, the ART
switch is in AUTO, either slat is extended, both engines are operating at or
near idle, and the ART system self-test is complete. The ART system is
subsequently armed when the N1 on both engines reaches 64% RPM.
The ART system is actuated when the DFGC detects any one of the
following: 30.2% differential in N1 RPM, invalid N1, DFGC failure,
electrical power loss, or manual DFGC switching. Upon actuation, the ART
system increases the EPR of the operating engine(s) from normal takeoff
EPR to maximum takeoff EPR (an increase of approximately .05 EPR) by
opening the solenoid-operated fuel valve in the engine fuel control. Once
ART is actuated, the maximum takeoff EPR limit is displayed on the thrust
rating indicator, and the EPR gauge. Once actuated, the ART system is
latched (ART fuel valve remains open) until the ART switch is moved to OFF.
The ART has an automatic self-test feature. If the ART system fails the selftest,
the ART INOP annunciation illuminates. Dispatch is allowed with a failed
self-test; however, the ART switch must be moved to OFF to disable the ART
system.
The ART switch, with AUTO and OFF positions, is on the upper instrument
panel. Two annunciator lights are on the center instrument panel. The
READY light indicates ART has successfully passed the self-test. The ART light
indicates the system has successfully activated.