Hudson River accident - FBW protections
roulishollandais
Correct me if I'm wrong, but I think you may be misinterpreting two sentences of the NTSB report into the Hudson Bay ditching:
"… the aircraft was in angle-of attack (AoA) protection from about 150 ft RA."
AND
"...Based on this explanation, it appears that on the accident flight, the nose-up side stick commands from 15:30:36 to 15:30:43 were offset somewhat by the phugoid-damping feedback term, thereby limiting the pitch angle and α increase below 150 ft radio altitude."
So, on the A320's ditching approach, Alpha-Prot Law was activated at 150R, because the AoA happened to reach alpha-prot at that height. It remained engaged thereafter because it takes priority over Normal Law, including the landing mode (which normally commences at 50R, and which at 30R starts to require an increasing amount of back-stick if the pilot wants the pitch-attitude to be maintained).
You state in your post, above:
I wonder too to see now the ref of 150 FT RA in the landing algorithm -Hudson- (and phugoid damping) which is much more than the most oftened read 100 FT RA or 50 or 30 FT : How could the crew and the Court know really how the system works?
So, on the Hudson approach, 150R was an arbitrary height at which Alpha-Prot Law had to take over from C* (Normal Law). In the extract quoted by HN39, the report does not state that the feedbacks used in Alpha-Prot Law - aimed at damping the pitch-phugoid tendency - change at any height. As for 100R, that is simply the height below which Alpha-Floor is inhibited.
However, it may be worth reminding ourselves that the Hudson accident was 20 years after Habsheim.
HN39,
FWIW, I don't regard any of your discussion about phugoid damping as semantic!