Each engine has its own -independent- two-channel FADEC.What is computed on #1 FADEC may be - and generally is - different from what #2 does.
Oops, yes, theoretically I knew that.You're right, these things aren't ever-present in my mind, since I don't fly the machines.
I don't have the ball park figure values on the Delta needed to trigger the A/THR disconnect (flying a different engine), I estimate it ~.2 EPR.
I read and re-read, and re-re-read the paragraph in the Taipei report appendix, and I think I've got it.
The bottom line is: A/THR disconnects when a thrust reverser is deployed.
It goes as follows:
- TLA readout corresponds to a certain EPR value
- TLA target EPR value is upper limit for autothrust
- A/THR working normally in speed mode, using engine #2
- TL #1 set to idle. No problem, just limits thrust usable by A/THR to idle
for that engine.
- TLA EPR value for Eng #1 becomes 0.98
- TL #1 set to reverse:
. TLA EPR becomes NCD ("no computed data")
. FMGC continues to use last valid value (0.98)
. FADEC uses a value of 0.75 with engine in reverse (FADEC EPR target feedback is upper limited to EPR TLA, EPR IDLE is reduced by 0.2 when reverser is deployed more than 15% (0.98 - 0.2 makes 0.78, but I assume that's close enough))
. comparison of the two values (0.98 and 0.75) is greater than 0.15.
. if that condition persists for more than 1.8s, A/THR disconnects.
This is consistent with the observed behaviour in the FDR graphs that A/THR disconnects about 2s after the thrust reverser was fully deployed on engine #1, at which time also EPR on engine #2 freezes.
Finally, there is still around the misconception that the CLB detent will deliver *Climb thrust*.
Yes, I originally wanted to write a sum-up of what happened to thrust and the thrust control systems in this accident, and show that at no point did the engine try to reach climb thrust or anywhere near it.