allwerp,
Airliners either can (A) recover normally from a fully developed stall, or (B) have on-board systems preventing stall entry, or (C) have fitted systems or aerodynamic assistance (such as strakes) to augment normal recovery from the stall. Without falling into one of these categories, the aircraft could not gain certification.
Don't confuse this issue with the deep stall discussion on another currently running thread. Having done a fair bit of testing work in endeavouring to take this category of aircraft beyond the normal stall into the "deep stall", the object of the testing was always to ascertain that recovery was possible. It always was. Not so for the poor souls who lost their lives during BAC-111 testing, but their legacy carried on to later generations of aircraft (and at the time caused Douglas to enlarge and redesign the Stabiliser/Elevator system on the DC9).
used2flyboeing, are you sure you're not confusing the DC9 with the B727? I flew both extensively, and clearly recall the very necessary hydraulic actuation of the elevators in a forward control push, but recall no such system on the B727. Maybe C.R.A.F.T's disease is catching up with me.
Regards,
Old Smokey