I'm well aware of the need for a powerful THS, as I suspect most every other pilot is also aware and that is PRECISELY the reason I find it disturbing that the Airbus THS operates without pilot awareness so much of the time. As this trim discussion continues, I find myself questioning the system more and more.
I don't mean to be critical here but why would you find the THS movement disturbing? It is part of every Airbus FBW aircraft and quite successful if recognition and acknowledgment of it, by the crew flying, acts in a reasonable manner. In the flight control operation section of the FCOM, the THS is described in Normal Law as to what it does. Then in Alternate Law (ALT 1), it is implicit, similar to normal law with limited pitch rate feedback and gains, depending on speed and configuration. ALT 2 is the same as ALT 1. Only in direct law does the auto trim stop when manual trim is required and noted by an amber message. The auto function/THS movement is the result of whatever is commanded by the PF in sidestick movement, back or forward.
I've thought about what took place after AP/AT disconnect on AF447. It quickly became an unorganized experiment in flight ending with the comment "We've tried everything". In reality it didn't have to be this way.
From an earlier
PJ2 posting in the AF447 Final Crew Conversation:
In my opinion as a (retired) A330 captain, the "safe conduct of the flight" was never an issue with regard to AF447, (and wasn't with all other similar UAS events).
However, "safe conduct" is a subjective, not objective decision-point in a critical drill/checklist and I think that is a problem that can lead the crew into an inappropriate and unnecessarily quick response.
A loss of airspeed indication is not an emergency, nor was immediate action required, especially of kind executed here which was uncoordinated, unilateral actions (meaning the absence of the use of SOPs) by the PF which went unchallenged by the PNF.
As discussed previously, all the crew had to do was to maintain pitch attitude and power setting as per the UAS QRH checklist while the abnormality was announced by the PF and the QRH called for so that precise pitch and power settings could be determined. There was no need to set a different pitch attitude at all.
I think this is partly 1) a drill/checklist problem, 2) partly a training problem and 3) partly a cockpit discipline problem.
1) the drill/checklist is poorly-written and confusing as to correct response, 2) their UAS training was done quite some time prior to this event on an A320 simulator, with the UAS occuring right after takeoff (requiring TOGA/15°) and not at cruise altitude which didn't require any action at all as the "safe conduct of the flight" was not in question, and 3) the cockpit discipline matter has been thoroughly discussed but there was a leadership-followership issue which was (and still is) a problem when two F/Os are in command of the flight, and the captain did not address how drills would be handled.
I don't think it can be said any better. The primary decision point was, "If the Safe Conduct of the Flight is Impacted" For AF447, it wasn't but the crew thought it was and they went set off in the wrong direction.
Aside from this on a more general note, there was an interesting revised book requested by the FAA and assembled by Airbus, Boeing, Flightsafety and various participating airlines and others. It issued prior to the AF447 accident, AF was not a participating airline but distribution of this to their flight crews could have been helpful. If you have not seen it, you can view it by going here:
http://flightsafety.org/files/AP_UpsetRecovery_Book.pdf