Originally Posted by
RetiredF4
You know very well that i´m fully aware about the functioning and the necessity of autotrim and do not question it. I even find it a clever and well thought out system. But the situation developing in ALT2 with AF447 was not being expected somehow and needs to be addressed and changed. It works in Alt1 at Vprot, why not do the same in Alt2? Nobody seems to be concerned to hinder autotrim in Direct Law, but you explain it would be difficult for the crew if autotrim would be hindered in Alt2 when predesigned values (aoa, speed, Trim value, take whatever would suit yourself) are reached?
Dropping autotrim in direct law already possibly killed several at perpignan, and similar change (although different system) probably contributed at schipol. I wouldn't say there is no concern about it.
The big problem with what you suggest is that the plane is in Alt22 because it doesn't
have trustworthy values for speed, aoa and possibly other airdata. So what should it stop trimming based on ?
The whole reason the protections drop out is because it has been held to be more dangerous to "protect" based on invalid (or not trusted) data, than to hand full unprotected control to the pilot. I suspect this is a certification issue. Boeing FBW is exactly the same (not sure about the newer bizjets).
That whole assumption may need to be challenged now - possibly we're reaching the point where safety will be improved by systems overriding / protecting pilots even based on known-bad airdata. Be careful what you wish for...