@ NARVAL
Thank You.
Not only the Crusader has deepstall : the Learjet of MICHEL BAROIN, father of FRANCOIS BAROIN, crashed in a dutch roll, followed by a deep stall... (february 5. 1987). Can the BEA remember that precedent fact ?
Only very very few people, and none in Congo from 1987, could imagine that the pilots would not be able to come out from the dutch roll and try to transform a murder in an accident, and how to organize that (As Dominique Lorentz wrote it in a book (1997 "Une guerre").
Surely the end of the AF447 diving under 45° in the ocean, looks like a deepstall. But "stable" is not the good word when we look BEA's report 3, annexe 4 :
Around 02h10m07s we can see the begining of a lateral autooscillation (page 115), and later around 02h11m40s we can see the begining of a longitudinal autooscillation (page 114). Oscillation does not go with "stability" in the automatician language.
It is strange too that the yaw damper began to oscillate at 02h09m35s, but very slightly. And the loos of IAS happened just after 2s delay in engine deicing : I don't affirm, but it would be well to study the case. Indeed a dutch roll can start on any aircraft when ice comes or goes away from the aircraft.
Another problem is the ability of any stall warning to prevent the deep stall : it is not the wing, but the whole aircraft who has a bad incidence.