For the life of me, I cannot remember how the EGT thermocouple gang does it’s job. There are 4 probes in parallel all connected to one output on a CF6-80C2. If one probe is removed from the equation, does the temperature indicated go up or down?
I ran into an issue today that caused me a bit of frustration... until I came up with a workaround.
Most of the fleet of B767s I have dealt with have an EICAS maintenance bypass switch, allowing the use of the maintenance buttons (ECS/MSG, PERF/APU, etc.) while the aircraft is in AIR mode, whether in flight or simulated with actuators. During troubleshooting of an ELEV FEEL EICAS (S) message the FIM requires the aircraft to be above 270 knots on aux. pitot system 1, hydraulics on, and the aircraft in AIR mode. Once these conditions are met, the ELEV FEEL message is able to be cleared.
But, what can be done if there is not an EICAS maintenance bypass switch?
The workaround I found was to pull relay K202 (which controls the EICAS maintenance function), jumper pins 10 and 11, then perform the FIM tasks. Once complete, reinstall the K202 relay after removing the jumper and move on to better tasks.