static stability and FBW laws
I am becoming increasingly disturbed by some of the assertions here regarding the longitudinal static stability characteristics of the 'bus.
From every document I can find, I see that the jet has a decent positive static stability characteristic. In short, the jet wants to achieve a trimmed AoA except for the actions of HAL. I see a feature that allows moving fuel aft to get a better configuration that relieves the HS/elevators from exerting a donward force. So we get lower "trim drag", and it's a good thing a lot of the time.
The cee gee of AF447 was nowhere near the aft cee gee that results in an unstable longitudinal static stability condition.
Thanks to Turbine, I have a limited explanation on the B777 control law philosophy. The thing seems to be more biased to AoA than to a gee command corrected for pitch. So this provides the "feelings" that many of us learned to deal with long ago. Trimmed for a low AoA and holding backstick, then release the stick and the sucker goes nosedown. And vice versa.
The actions of a cosmic FBW system that overcomes the basic aero characteristics of the jet can be neat, but can be fatal.
I can only speak from my experience in the first fully FBW jet to be fielded in more than a handful of airframes or test vehicles. The Earth was still cooling. Anybody else here with such experience would be welcome to contribute to this discussion.
As with the 'bus, our FBW system was heavily biased toward gee command. We didn't see a significant AoA contribution unless pulling hard and getting slow. So we were basically speed neutral in level flight and only basic aero drag kept us from getting faster and faster or or vice versa. No big deal, as we didn't spend hours of "monitoring" the computers.
The gee command of the 'bus is a major factor in moving the THS. The system tries to reduce the pilot stick pressure for the commanded gee. NOT THE AoA!!!!! Boeing seems to like the AoA for trimming.
So the BEA report correctly points out that the jet would have gone into test pilot conditions with the pilot commanding neutral stick once the pitch attitude and power setting allowed it to enter a stall.
The 'bus FBW laws' emphasis upon gee command and the lack of attention to AoA inputs was a major contribution to this incident. I completel;y agree with the others here that holding initial attitude and power for "x" seconds would have saved the day.
I would hope that the major carriers would try to expose their pilots to some of the edges of the envelope either in the sim or the actual jet.