Nose down side stick would have "corrected" the THS whether they recognized the setting or not. Recognizing that nose down was required was the issue.
Correct. It even actually
had corrected and the THS was not stuck in its rear position. You can read that from annex 3, page 3 (raw DFDR data, right elevator position): Once the stick was pushed forward at 2:12:34 or 2:13:47, the THS moved in the forward direction. They just should have let go with the stick.
Autotrim was not an issue.
The integrator never unwound over the rest of the flight (fall) to impact.
It did. See above.
This was the reason for AP disconnect on AF 447 which subsequently led to the demise of the aircraft and all on board!
No AP disconnect is any reason to get scared. If pilots can't fly the aircraft without AP, they shouldn't be sitting in the first row.
6: If I remember well some fuel had been transferred to the tail (which I suppose happens automatically during cruise, like on MD11, to reduce fuel consumption) making it even more hopeless, if they wanted and had tried, to exit the condition of deep stall they were in.
I understand your question is whether they would have been able to exit the stall (not so much about the trim logic itself). I say:
yes. You see in annex 3, page 6, that every significant "stick down" input was followed by a) THS forward movement, b) pitch decrease and c) airspeed increase.
Is there a ready explanation for the very smooth line of THS increase to max, vice a more herky response to actual (commanded) pilot inputs? It looks graphically as though the THS was deploying to a "target" position, independent of pilot command?
Yes, it's a smoothing function, designed to reduce stick workload. It never ceased to react to stick inputs, see above. The sticks were just pulled too much almost all the time. (Should answer deSitters question as well: It wasn't an obstacle.)
The aircraft data say it more precisely than any statistics and sattelite imagery: The icing indicator never indicated anything, turbulences were only "light" by ICAO standards. So, "storm" wasn't a factor, as pointed out several times now. Except for creating an atmosphere where icing could happen to the pitot tubes without being indicated... but that is not limited to thunderstorms or the ITCZ. The flight path was choosen carefully right, at least
one error they
didn't make.
As to usage of pitot tubes: Mass flow sensors need an additional (second) temperature sensor. Which can fail. Heating can fail. The metering wire can rip while flying through hail. These failures are interrelated with AND, multiplying failure probabilities.
Pitot tubes indicate
indicated airspeed (IAS), which takes air density automatically into account, by physics, not by processor. Quite convenient. GPS (ground) speed is no feasible backup - ever heard of upper winds, let alone jet streams that can make 100 knots difference? It's airspeed that makes an airplane fly, not ground speed. The difference is the wind, which hast to be measured. There you are again with
air speed.
And there is sort of a backup sensor for the pitot tubes, which is the AOA sensor. You could hand fly the airplane without speed, just with AOA. But if even the stall warning gets ignored altogether...
angelorange, thanks to bring back the Airbus publication
FAST #24. It is especially interesting to read CPT Wainwrights comment on the "fighter style" recovery actions that are proposed every now and then, as well as his warning to teach deep stall in the simulator, which could lead to completely wrong conclusions (the simulators do not simulate deep stall).
EDIT: For those that have not yet read, I like to quote the Airbus Chief Test Pilot in said article:
We manufacturers were very concerned over the types of manoeuvres being flown in simulators and the conclusions that were being drawn from them. Simulators, like any computer system, are only as good as the data that goes into them. [...] It should be obvious that firm conclusions about aircraft behaviour can only be drawn from the parts of the flight envelope that are based on hard data.
In fact, this is a perfectly adequate coverage to conduct all normal training needs. But it is insufficient to evaluate recovery techniques from loss of control incidents. Whereas, the training managers were all in the habit of demonstrating the handling characteristics beyond the stall; often telling their trainees that the rudder is far more effective than aileron and induces less drag and has no vices! In short, they were developing handling techniques from simulators that were outside their guaranteed domain. [...] It is worth saying that there was never any difference of opinion between the three test pilots on the group. [Airbus, Boeing, Bombardier]
And, with
Boeing's words:
However, airplane upsets often will involve g load excursions and these cannot be duplicated within the simulator environment. They have not been designed for the purpose of replicating upsets, and as such, whenever maneuvering involves vertical or lateral loading, the realism degrades.
This is a very important point for both the trainee and the instructor. Instructional content must acknowledge this limitation and fortify instructional content based upon the trainee’s prior flight experience with g load excursions. Without this instructional input, a positive learning goal can be transformed into a negative learning experience. [...] However, flight data are not typically available for conditions where flight testing would be very hazardous.
So, very limited use to conclude from sim experience to real life once talking about stall.
The AF447 crew's lack of CRM reminds me on an opposite case with
Lufthansa on 20th March 2001, where the crew faced a major stick malfunction just after take off. Since they changed control immediately, everybody survived. In the mentioned incident (
BFU report in German), the captain (PF) recognised that his actions were in vain and handed over... that saved the day. AF447 had several minutes to see that pulling the stick was in vain, not just seconds!
These are my main questions as to the crew's psychology: Why did nobody of FO or CP take control earlier, e. g. the captain request to sit in his chair and see for himself, and second why was the SO trying on his own for so long without requesting the others to take over? I'm sure I would ask for help / take over.
The only potentially explaining metal picture I have of the PF is that he was feeling very uncomfortable, in particular at this altitude which he considered to be too low (asked the CP to climb, but this was refused). He even wasn't familiar with St. Elmo's fire. Not the best precondition to master the next events. So the very first action after AP disconnect was to pull the stick.
The aircraft climbed accordingly. And the altitude increased
unnoticed EDIT correction: without consequences. Why? What was the PNF doing? This is puzzling me just as much as why the PF was pulling all the time.