Machinbird;
Your welcome.
I know you and a few here will understand the processes behind the imagination and design capability required to create a reliable, predictable fly-by-wire control system. But there are misgivings about fbw sufficiently expressed here that I thought a comment or two was needed. I say this because I don't believe for one moment that "flight control laws" are in any way associated with this accident. This is not eliminating AFS matters, nor by virtue of exclusion does this now automatically point to "flight crew". The matter is subtle; Like others, I think we are going to learn lots. I think the cost of such learning is, however, unbelievably tragic and frankly intolerable.
I need to say that the document to which I referred should not be taken as "current" and that no attributions connecting the document with AF 447 should be made. While I do not claim to understand the mathematics presented, it is very clear from the thoroughness of the document that "flight control laws" in civil aircraft are not unexplored areas with many unknowns and, as stated, this paper was presented in 1993, thirty years after fbw technology was initiated. There is plenty of experience here.
The author states in this document that the B747 isn't a suitable platform for validating the C* parameter because "it was too stable a platform", (given the original military origin of C* and the desire to control neutrally-stable fighters)! Quite a back-handed complement in my view. Nevertheless I understood enough in the document to know that there was much more behind every stick movement I made on the A330, than I had appreciated.
The intent of posting the paper wasn't to bolster any view; it was to convey to some contributors on the thread who I believe don't fly, or have never flown an Airbus or specifically the A330 and who seem to believe that flight control laws have something to do with this accident, and that a perceived "rudimentary" nature of the A330 flight control laws threatens to leave pilots in the lurch at the most critical moment, and that these laws are squirrelly (even roguish), and that they do unpredictable things that are beyond the control of the pilot, and that they were not vetted thoroughly when designed, and that because they are subject to continuous improvement is proof that at one time they were "dangerous", and, the most humorous remark of all, that there are "too many laws", which brings to mind Emperor Joseph II's remark to Mozart upon hearing The Marriage of Figaro for the first time that there were "too many notes". Too many servos?...too much wiring?... I think the point is gently made. That said, the C* Law is not about protections, it is a non-numerical parameter which defines how fbw interfaces with flight controls. "Protections", came with digital capability. In this, we need to ask not about too many laws, but are such requirements for a sophisticated AFS sufficiently transparent to the user? I think that is a legitimate question.
I think flight crews here will concur that there is no mistaking what an A330 pointed up a 16deg pitch attitude at 37,500ft, at 215 kts with a rapidly decreasing airspeed, is going very shortly to do.
Yet, according to the BEA Report, back stick was held throughout. Further, though THS was continuously, though manually available, no one rolled the trim wheel forward.
The answer to the pitch up and loss of control is not to be found in the minutae of flight control laws even though as a result of flight well beyond the boundaries of controlled flight, the flight control laws responded "as designed".
I believe that an answer may be formed by a deeper understanding not of flight control laws but of what, and why it made sense to the PF to maintain back stick pressure when for about three minutes after the start of the stall at 38,000ft, the descent rate could not be arrested.
For sure this isn't second guessing the PF or hindsight bias. The BEA Report is clear on the back-stick position throughout the recording.
gums and NoD are completely correct to observe first, that overspeeding the airplane, (which, in practise would never occur or for that matter even be necessary), is far preferable even to the maximum dive speed plus, than moving the stick back which would make a loss of energy inevitable. At least on the way to an overspeed, recovery would occur at some point, and second, to NoD's point, at what juncture must the designer continue to intervene through software and, in the present case, provide stall warnings below a chosen speed, here, 60kts? Besides the stall warnings which did operate, the aircraft provided the same cues as any other in such circumstances...buffet and an unstoppable descent.
At what point may we claim "too many laws", while saying that such interventions also have the characteristic of impairing and inhibiting pilot awareness, response and control? Who is capable of determining that point to the satisfaction of those who actually did the work. Peter Mellor's change of heart was cited earlier in the thread by Dozy. A re-read is indicated.
A fuel imbalance, an unintended stick input, an asymmetric thrust/rudder input are all possible factors in the right-roll. The event that was behind the Perpignan accident, and cause of the A340 AIRPROX event are almost certainly not behind the pitch-up after the AFS/AT disconnected.
I have said many times that I do not "defend" the A330 so much desire that any criticism come not from a personal bias against autoflight or other areas which are not widely claimed by others, but if one is going to claim something, I think it is fair to say it should come from a keen knowledge of systems, (if this is to really be a Tech Forum). That approach is a very different matter than claiming that the A330 is pristine and without fault.