Rat,art,atr
In the MD,the RAT probe send temp data into Air Data Computers.These, in digital format feed both digital flight guidance computers.The DFGC compute the EPR for each flight phase and pilot seleccion through the TRP(thrust rating panel).The RAT probe is heated only in flight for anti ice purpose.If for some reason,the ground sensing relays ( energized in ground) change to flight condition,the Rat sensor is heated and the EPR is reduced. This change may be for a circuit breaker open or a ground sensor relay fail .This condition may afected the takeoff condition warning too.All of this is not too much evident for pilots.
The ART ( automatic reserve trhust) is used only in normal TO EPR. Not in flex. or max. Is activated when the DFGC sense diferences (30 % ) between both N1 .Not is autothrottle funtion but inside the fuel control unit. Increase about 700 lbs thrust or .05 EPR to the present thrust.
The ATR ( auto thrust restoration) with the last DFGCs (-972 and subsequent ) only is active in noise reduction cutback procedures.
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