CONF - read what I'm saying carefully. The limiting protections are not assigned to each of the flight controls in turn, the flight control computers simply command a flight path, and when an axis limit is reached, maintain the flight path in said axis. The THS (and for that matter elevators, ailerons etc) are not prescribed movement limits in real-time (which would be inefficient and unnecessarily complex), they are set to follow the commanded flightpath, whatever that may be.
When the protections are inhibited in Alternate Law 2, the pitch axis is still controlled by the commanded flightpath, but the flightpath no longer has a hard or soft limit. As such the THS and elevator will follow any command given from the stick, which makes sense as long as you're willing to trust the pilot.
So - on that basis, the systems designer faces a dilemma. Do they add an autotrim limit or warning based on the current status of the aircraft? Would doing so run the risk of making things worse? Is it worth taking that risk on the basis of a single incident where the control inputs made by the PIC were woefully inappropriate?
At the risk of repeating myself, the autotrim would have assisted in the recovery if the PIC had ordered sustained and consistent nose-down. It would have stopped dead and slowly recalibrated itself if he'd levelled off at any point prior to the apogee and stall.
Even if autotrim was limited or disabled in Alternate, the end result of AF447 would have been the same because the fact we cannot escape from is that the PIC pulled up at the onset of UAS, continued pulling up during the climb, and kept pulling all the way thorough stall and descent to the ocean.
PS. I wasn't bringing up Habsheim to talk about Habsheim, I was simply drawing your attention to the behaviour of the flight surfaces in that incident to illustrate my point. I did so because I know you're very familiar with it.
Last edited by DozyWannabe; 10th August 2012 at 19:27.