There are some (who know their aerodynamics) who have done some work on this and who believe that the airplane could be recovered, even from quite low altitudes, (thicker air). The horizontal stabilizer was never fully stalled and the airplane demonstrated the ability to pitch down when ND stick was held those rare times in the ND position.
Thanks, that's the bit of information I was looking for. Clarification, when I say "deep stall", I don't mean to imply an unrecoverable stall condition (such as what happed on the BAC 111), but rather a sustained stall condition where the aircraft is going down as fast (or faster) than it's going forward. As I understand it, on the BAC 111 (and some other 'T' tail aircraft), if you get into a deep stall, the spoiled airflow from the wing effectively blanked the tail and literally prevented pushing the nose back down to recover.
I've been on flight tests where they did dozens of stalls and "wind up turns". I suspect most of you are unfamiliar with that term so I'll explain - for a 'normal stall test, the pilot holds a constant altitude while allowing airspeed to decay (throttles at or near idle) until the aircraft stalls. These stalls are pretty gentle (at least on the 767 I was on) - a little forward push and the airplane falls out of the stall and recovers (although if the pilot had to use a big rudder input to keep it straight and level, the rudder would tend to shear the line to the 'trailing cone' Pamb sensor - in which case we got to go home early
). A 'windup' turn was used to test the inlet at very high angles of attack with the engines at takeoff power - hold constant altitude but pull the turn ever tighter until the aircraft stalled and fell out of the turn. It's basically a way to test the engine inlet reaction to a takeoff over rotation, without doing it a few feet off the ground. Three hours of windup turns is also the only time I've gotten airsick (straight stalls didn't bother me, but windup turns did).
Anyway, back to the point - in a deep stall, with forward airspeeds well below that necessary for level flight - even if the horizontal stab isn't stalled, it's not going to provide much authority - simply not enough Q. It's going to take a
long time to push the nose down enough start gaining sufficient airspeed to regain control.
Back during the original 777 flight test, an unnamed FAA pilot somehow managed to get into a deep stall at high altitude - even though the right seat Boeing pilot immediately took control, they reportedly lost over 10,000 feet before he was able to regain control (second hand info - I wasn't on that flight and I'm pretty sure I'm glad I wasn't
).
Again, PF kept sidestick forward for 10 sec. He was a glider pilot too, imagine that input for a glider
Yea, while 10 seconds probably felt like an eternity, in a deep stall I suspect at least 30 seconds just to get the nose down and get airspeed up to a reasonable, controllable level.
For me, as a non-pilot who once knew a bit about making stuff that flies, the single most scary thing from all the 447 and other stall threads has been the number of apparent pilots who don't seem to know this.
Ditto! And the idea that one can power out of stall by advancing the throttles has a potentially fatal flaw - engine inlets are not designed to provide high flow at those angles of attack. Inlet separation and engine stall is a distinct possibility (reportedly one engine stalled/surged during the Birgenair 757 plunge)