Chris Scott
Reply from HN39:
"Was it ? ...."
I'm rather hoping you can answer that, HN39. After the overspeed of Mach triggered the disengagement of the AP, was the peak Mach of M0.882 corrected by EFCS overspeed protection, involving a pitch-up with neutral sidesticks?
Why me? I probably know much less of the airplane than you do. My understanding is that activation/deactivation of any protection is recorded by the DFDR by a dedicated discrete parameter changing from OFF to ON, from ZERO to ONE, or whatever, and vice versa. (*) I think it would have been a very strange omission if overspeed protection had been activated and caused the pitch-up and the AAIB report had made no mention of that fact. It says instead: "For 18 seconds after the autopilot disengaged the aircraft remained within 200 feet altitude of FL 360 but once AoA law was invoked at 14:21:50 hrs, the aircraft’s attitude began to pitch nose-up."
On the other hand, did the rise of CAS in itself cause or contribute aerodynamically to the pitch-up? And what effect would such a rise of pitch have on the AoA, and its rate-of-change?
Perhaps Owain G is better placed to answer that question. I think that an increase of CAS does not cause a pitch-up. It causes an increase of lift, and hence loadfactor ('gee'), and an AND response of the FCS in Nz law.
(*) A single byte in the data frame can contain up to eight 'discretes', each bit indicating the on/off status of a particular system function.
P.S.
I found a rather interesting description of the phase-advance logic for the A320 in this accident report:
"http://www.rvs.uni-bielefeld.de/publications/compendium/incidents_and_accidents/EC-HKJ.pdf"
The url failed for me, you have to go to PBL's site "rvs.uni-bielefeld.de" and follow the crumb-trail to the report.
Please note that this describes the A320 system and not the A330/340.