Rewrote post 708 (in order to try and understand its ramifications)
ref the return to the ramp......
In the MD-82, the RAT probe sends temp data into the Air Data Computers.This data, in digital format, feeds both digital flight guidance computers.The DFGCs compute the EPR for each flight phase and for pilot selection through the TRP (thrust rating panel).The RAT probe is heated only in flight for anti-ice purpose. If, for some reason, the ground/air sensing relays (energized on the ground) change to an inflight condition, the RAT sensor is heated and the EPR is reduced. This change may be due to a circuit breaker opening (or a ground/flight sensor relay CB being left open by the mech after he deactivated the system? - shades of Helios?) or a ground/air sensor relay failing .This condition may affect the takeoff condition warning too. None of these prospective developments would be evident to the pilots.
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The ART (automatic reserve thrust) is used only in normal T/O EPR. i.e. not in flex. or max. It's activated when the DFGC senses a difference of 30% between both N1 gauges. It's not an autothrottle function but carried out inside the fuel control unit. Its effective increase is about 700 lbs thrust or .05 EPR to the present thrust. The ATR ( auto thrust restoration) with the last DFGCs (-972 and subsequent ) is only active in noise reduction cutback procedures.