After further reading (if I understand this correctly), on CF6's, a comparison is made between the two T12 (engine inlet temp) sensors and if they disagree with the airplane sensor, then the EEC's switch to a soft reversionary mode.
I guess, there being 2 engine sensors, it would be easy to see if the aircraft sensors are faulty.
My notes say that a soft reversionary mode may cause thrust asymmetry, so I guess it's not what you want on takeoff. There are associated EICAS messages with soft reversion, so I guess the crew wouldn't even get as far as the runway with an airplane TAT so different from the engine sensors.
My schematics show information from two ADC's going to
each FMC (via the Instrument Source Select switches) complicating the matter further. The only way I can see of forcing the FMC to use the Right TAT probe is to select both ADC Instrument Source Switches to Centre. The ISSS's offer onside or Centre ADC info to the FMC, the Centre ADC being fed by the second element in the Right TAT probe.
BTW, Cornish Jack is right 99.9% of the time, so if he's wrong this time, I'll forgive him
