Lonewolf_50;
System failure is (based on information so far gleaned) the trigger. BEA had taken that tack long before the wreckage undersea was finally located. Pitot tube issues and recommendations pre-dated the retrieval of the FDRs. It appears that their first estimate was well formed.
The event chain needed a trigger. Absent airspeed system failure, transition out of normal law and trimmed/stable flight state not likely => thus manual flying not required => thus the curious 30 second input not induced=> and so on.
If you wish to focus on human factors, you'll get no argument from me, but the linkage to mechanical factors is critical to the event chain. (There is a valid line of inquiry regarding "how well do you know your machine, and how well can you know your machine?" that was much discussed in one of the earlier threads, over a year ago I think).
How a response to airspeed system malfunction issues should have been addressed, and how the training of crews should have been undertaken for a known failure mode, certainly points to the human factors which include systemic / corporate / cultural human factors.
Getting into a stall in this event chain is a subordinate line of inquiry to response to malfunction. Per your earlier perkins reference, this points to a systemic issue that gums raised.
If you don't expect a stall, if you aren't familiar with what it feels and looks like, and if you don't train for it (<= not sure how valid that statement is, training may vary considerably) it is quite possible to initially react in a sub optimal manner. At that point, you are playing catch up, or as we used to say, you are behind the aircraft.
Very well summarized - agree fully.
BOAC;
I still await ANYONE who can tell me how autotrim relates to 'received' IAS input OR what baro indications the crew actually were left with. Of more interest than a hairy bat?
The BEA mini-Report cites altitudes a number of times so the parameters depicting altitude were working. There are no ACARS messages which indicate that the DMCs [Display Monitor Computers] were malfunctioning and no indications that static ports were involved. My sense of it is that the altimeters were functioning normally and I think the assumption is a reasonable one.
The autotrim does not "relate to 'received' IAS". As has been discussed, (
gums, Chris Scott, Machinbird et al), pitch control is 'gee-driven' (Nz Law) in Normal and Alternate 1 & 2 Laws. In Direct Law the airplane is a B737...you have to trim it manually; no big deal, if it's trained and encouraged.
For emergency backup of GW and CG computation in case of a dual failure of the two FCMCs, [Fuel Control Monitoring Computers], the FE [Flight Envelope] part of the FMGECs calculates the GW from the WFU [Weight Fuel Used] and the CG from the THS position. The CG calculated here is a function of N1, Vc, Altitude, Mach and the GW from the FE part of the FMGEC and is memorized for used in the event of the above-mentioned dual failure, (IOW the airplane has to have something to fall back on whether in Normal or Alternate Laws because autotrim still functions in both laws).
In Direct Law, pitch trim is manually controlled through the two trim wheels on the pedestal. Manual trim is available in all phases of flight in all laws.
It is a complete mystery to me why it has been said that the use of manual trim is "discouraged". The issue is
one of many which requires examination in the manner described by
Lonewolf_50, (quoted above),
Chris Scott, Machinbird, gums and others. (The Final Report will indeed be very challenging to write.)
Simplified, in Normal and Alternate Laws, movement of the trim wheels disengages the autotrim function during wheel movement but re-engages the autotrim when movement stops. The trim will move back to a position ordered through the AFS [Auto Flight System], which, as stated, is 'gee-driven', again, very simplified.
I think the anecdote about bats is instructive and helpful as well as fascinating...after all, the Wrights learned from observing birds did they not?... ;-)
Regarding the training of the approach to the stall, (Stall recovery is not taught at all, to my knowledge), not only the manufacturer stated, but many regulators and certainly operators, bought into the notion that the airplane was protected against the stall. Those of us who checked out on the airplane early enough to dismiss such claims, (EVERY airplane can be stalled), flew it with the usual regard for the conservation of energy. Someone said that except at takeoff, a 10° pitch attitude in any transport aircraft was cause for serious concern, (or words to that effect). Damn right. But somehow along the way, the mythology became established and that requires examination because automation in and of itself does enhance flight safety, but it has to be used as intended.
gums is right...the word "protections" is a misnomer and "limits" describes it better, but the former conveys a sense of security while the latter is merely descriptive. Bluntly speaking, one is a marketing term, the other is an aviation term.
I hope this is of some use,
BOAC.