Originally Posted by
Chris Scott
The BEA report states that, in their configuration (Flaps 3 and L/G):
alpha-prot was 14.5 deg;
alpha-max was 17.5 deg.
At t = 0 ("impact") both pitch and alpha were about +15. The latter represents the apparent discrepancy of about 2.5 deg that Conf_iture has called into question. As stated above, alpha-max can only be achieved by sustained, full back-stick.
Indeed, I think Conf_iture is comparing the "17.5° AoA = AlphaMax" from § 1.16.1.2 and the column labelled "INC" (short for Incidence = AoA) in the FDR annex (page 37 of the french original PDF report). We see on that chart that in the end of the flight (~12h45'33"), the AoA reaches and maintains 15°.
17.5 - 15 = 2.5. There we are.
Originally Posted by
CONF iture
The BEA does not elaborate at all but applying full back stick is what it takes to go to alpha max.
Full deflection in roll is 20 deg but 16 in pitch. The stick was fully back.
Thanks for the value (16=max deflection), was looking for it.
Two remarks, regarding your point:
1/ I think the last column of values (in the FDR annex) are the decimals for the AoA. If I'm correct, then the last AoA value registerd is 15.4°, not 15°. The aircraft would have been then 2.1° short of AlphaMax, not 2.5.
[edit] This remark prooved to be null and void, as pointed by Conf below. Disregard, sorry.
2/ Between timestamps 1245.328 and 1245.335, the registered AoA varies between 2 extreme values of 13° and 15°. This variation led me to believe that, either:
- something prevented the aircraft to reach AlphaMax despite the crew demand (some are advocating this, but no you, unless I'm mistaken),
- or calculated AlphaMax at the time was lower than theorical max AlphaMax of 17.5° (DW... why?),
- or that the crew did not maintain full aft back stick. You said above that the crew did. Ahem... really?
Do we have reliable sources on that topic? In fact, yes: the very same report. See: Why AF A320 didn’t reach AlphaMax @ Habsheim.
My conclusion: indeed, as Conf_iture said, the aircraft did not reach AlphaMax. Because the pilot didn't ask for it (unless, perhaps, at the very last second, i.e. too late).
Your explanation as to why is there:
Originally Posted by
CONF iture
Late in the sequence, the pilot, now fully aware of the approaching trees, but well aware that thrust was not coming as he expected it, delayed as long as possible the pull up request.
That doesn't sound logical if the pilot had decided to rely on the AoA protection, because as you said yourself, to get AlphaMax you have to pull the stick full aft and maintain it there.