Lemurian, thanks for your reply. Please bear with me some more ...
You seem to have a better understanding of the thrust control system's terms, I'd greatly appreciate it if you could read p148 of the incident report of the Taipei-Sungshan-Overrun (
http://www.asc.gov.tw/acd_files/189-c1contupload.pdf), and tell me what I understood wrong.
- A/THR working normally in speed mode, using engine #2
Hm, yes, obviously.
[QUOTE]
- 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
There is the first disconnect condition as in this case, TLA #1 EPR < FADEC target EPR - .2 (?)
TL#1 is pulled to idle at around 18:48:22, A/THR only disconnects at 18:48:29. So it seems this was not the case.
- TL #1 set to reverse:
. TLA EPR becomes NCD ("no computed data")
. FMGC continues to use last valid value (0.98)
No, the same 1.2 EPR needed to maintain the approach speed and which was applied to #2 engine after the deconnection.
FMGC uses 0.98 (last valid) as TLA EPR value. The report again:
the FMGC ARINC acquisition behaviour (per design) in case of NCD is to keep the last EPR TLA valid value.
It also says,
the condition triggers when the "THR TARGET feedback of one FADEC is different by 0.15 from the ATHR EPR TARGET limited to the corresponding EPR TLA.
. 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.
2nd disconnect condition"
According to Airbus, this condition was the one triggering the disconnect in Taipei-Sungshan. Doesn't mean it has to be, here, but the timing implies it.