Thanks to everybody for the detailed information apported on the subject.
Do you agree if we say that the tail structure has been loosing part of the aeroelastic design characterics (i.e. lower resonance frequencies) and have been disturbed by the wake (acting as the dist. forces)?
I know for examples that BAe146 has big problems on the tail (pitch oscillation)where the left/right elevators became anti-symmetrically oscillating at high frequencies and the only solution is to reduce the speed.
My condolences to all the people that have lost their lives.
Cheers.