vilas,
As you know, this thread was started from the transfer of a few posts on the AF447 Thread No. 11. (Not my idea!)
If you look again at post #1, you may be reminded that - in an earlier post on the AF 447 thread - I had opined that the crew had been relying on Alpha-Floor to initiate the G/A (i.e., when the AoA reached +15), but that they had allowed the a/c to sink below the Alpha-Floor inhibition height without realising the consequences. That assumption on my part was naive, and on reflection would have made it very difficult for the captain to go around at a position (in relation to the crowd) of his choosing. Alpha-floor (+15 deg) is only half a degree above alpha-prot.
As CONF_iture pointed out, however, the captain had specifically briefed that he would be inhibiting Alpha-Floor, in order to continue pitching up to alpha-max. His plan was to maintain alpha-max (therefore necessitating full back-stick) in level flight (he said at 100ft), using manual thrust to maintain height. (Note that, at a stedy AoA, thrust controls VS, not speed - rather more like a light piston-engined a/c on the approach.)
The two key defficiencies in the execution of the briefed game-plan seem to have been:
(1) Rushed, straight-in approach, arriving over the airfield boundary (inbound) with too much energy to allow a reduction in speed to the planned Valpha-max during the transit of an unfamiliarly-small airfield. This may have tempted the PF to delay the go-around while he waited for the IAS to decay to an acceptable (in his terms) value.
(2) Descent below 100R. From the time they were approaching 100 ft on the approach until about t -3, the PF consistently did not pull hard enough on the stick to maintain or recover to the briefed height. This apparent reluctance to pull harder is all the harder to explain, because the PF was looking for the highest-possible deck angle to show the crowd.
Quote from CONF_iture:
Originally Posted by Chris Scott:
"Note that this BEA description does not specify that an alpha of 17.5 deg will be achieved if the pilot maintains full back-stick."
The BEA does not elaborate at all but applying full back stick is what it takes to go to alpha max.
Yes, we are in accord on that one.
However, in the earlier post you've quoted, I was just trying to point out that the BEA seems to have carefully emphasised that alpha-max (in this case 17.5 deg) will not be exceeded, without stating that it will necessarily be precisely achieved.
Quote from CONF_iture:
"Full deflection in roll is 20 deg but 16 in pitch."
Thanks, I haven't found that figure yet. The DFDR trace seems to shows a rapid rise to about -17, at which point the trace ends without becoming steady.
Quote from CONF_iture:
"The stick was fully back."
As I've already said:
"Between t -9 and t -4, the stick command was between -6 deg and -7 deg, but this was relaxed slightly at t -4, falling to -5 deg.
"The last recorded stick position was -17 deg (17 deg nose-up command), rising rapidly from -5 deg at about t -3."
The back-stick reached about 17 deg (presumably maximum), but not for a measurable period prior to impact. That's the reason for my observation in (2), above. Why he did not pull harder from t -26 to t -3 is inexplicable, if only because it was delaying the desired attainment of alpha-max. The modest back-stick up to t -4 would, as you know, never achieve alpha-max.