Originally Posted by
Leonakua
So this has been unclear to me. On TakeOff, with both in TOGA, say NUMBER TWO fails. Not yet at V1, PF retards both levers, number two because he/she knows it has Failed, and number one because he/she rejects the rotation ..
Assuming each engine is isolated from the other, Including TCMA, will both shut down independently, and "simultaneously"? Even though engine data is read as quite different? Asking if the airframe logic can suss the difference twixt legitimate
Dual shutdown and airborne dual shutdown?
Mode logic confusion... Thank you tdracer
If asked before, was the one second sample rate considered? Seems relying on steam sensors (WoW, levers discrepancy, etc) might conflict with instant FADECS??
If this is accurate, and TCMA " Does not care about acceleration, I see a problem.
Once WoW has triggered TCMA, once and done. No? Because I give TCMA. NO leeway. If it advanced thrust on a landing, it's locked out, full stop. Eh?
First off, WoW, Lever angles, etc. are not "one second' - they are basically instantaneous. Thrust lever angle is read directly by the FADEC, at the FADEC 'minor frame' update rate (not sure about the Trent, the GEnx minor frame is 15 milliseconds). Once per second is the update rate for most parameters on the FDR - it's not the update rate the avionics use. I don't know specifics of the 787, but on the 747-8 the update rate for Wow and Radio Alt was about 10 times/second - I'd expect the ethernet based network on the 787 to be faster.
Let me say this again - TCMA will only take action if the engine is
not responding normally to thrust lever movements. We use flight test data to validate the rates that we expect the engine to respond to lever movements, then add ~20% margin to that. So if you do an RTO because one engine failed, TCMA won't do anything on the good engine
unless the engine stays at high power after the thrust lever is retarded. It's not related to the aircraft speed or acceleration rate - it's all to do with how the engine is reacting to what the thrust lever inputs are telling it to do.