For 757 ,
when the TAT heater is inoperative on single TAT aircraft, the TMC considers temperature from the TAT to be invalid and disconnects the autothrottle. On dual TAT aircraft, airplane systems use the unaffected TAT signal when reconfigured to use Center Air Data.
With an inoperative Thrust Management Computer, the Autothrottle System will be inoperative and
the following displays on EICAS will be affected:
1. EGT (and N1, N2, N3 for RR engines) amber indications which are normally inhibited during takeoff or go-around will not be inhibited,
2. Reference EPR will not be available,
3. Assumed temperature (if used) will not be available,
4. Thrust reference mode (TO, CLB, etc.) will not be available.
5. Airplanes that do not have speed tape: the SPD flag may remain in view on the EADI.
With reference FADEC engines, if TAT probe heat fails EEC wiil receive an TAT invalid signal and default to using its own temp sensor ( aircraft data being preference .)
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