Follow on from post #2772 ( TU-154 flat spin accident).
From Air Safety Week (Sept 18th 2006), and although focused on T-tail aircraft incidents, some of the findings regarding vertical velocity/ trajectory under stall may be pertinent to the current discussion.
A Tale of Two T-Tails | Air Safety Week | Find Articles at BNET
Re: MD82 crash (Preliminary) AUGUST 2006 (WCA708)
Quote (page3):
"the engines wouldn't have recovered until gulping much denser air at the lower altitudes, shortly before impact at their descent rate of over
7000ft/min."
...."According to the Flight Recorder, WCA708 descended at a
high angle-of-attack "
Quote (page 4) :
"The descent from FL330 took 210 seconds. The debris field was only 200m long and 110m wide, indicating a near vertical descent with no forward airspeed. The crew had radioed that "both engines had flamed out" but they were merely locked back at flight idle."
Although this makes extremely interesting reading, i think that the T-Tail element of these aircraft mentioned is important. They have chracteristics in which the aircraft can enter a 'Deep Stall' in which certain configuration's of stall upsets can also lose all lift (whether negative or postive) on the horizontal stabilser and elevator as well as the wing. This renders the elevator as useless.
From my days at the flying school and physics lectures, i seem to remember that these upsets are impossible to retrieve from. All T-Tail types are affected, 1-11, MD80 series etc....
I think that AF447 will not have been affect by a 'Deep-Stall', due to the airframe characteristics, but stall scenarios are not fully tested by AB, for the obvious reasons.
I think the idea that big jets cannot (mentioned elsewhere in this thread) spin, is preposterous! The fact that one wing can lose lift quicker than the other one is a factor for all types IMHO and is a function of physics, not engineering.
Maybe there is an argument for can certain big-jet types flat spin, but how would we know, obv. it is not tested, and if types have spun before i could imagine the airframe not standing up to it. I think the idea, that the aircraft
might have spun, should be given some creedence. Considering at one moment it was @ FL350, and within a short timeframe, in the water. This combined with BEA's
fact (that is how i read it, not an assumption) that the aircraft hit the water relatively flat with a strong vertical acceleration (acceleration = rate of change of velocity over time), combined with a low forward speed, suggest's to me that a stall scenario occured.
Speculative questions from me include:
Why would a normal stall scenario cause this from FL350 or below? considering there might have been enough height to recover...IMHO there would be fugoid osscillation on attitude, splitting between excessive pitching moments in the vertical plane, possibly exceeding overspeed and stall
Given that the type possibly cannot 'Deep Stall' (given by research by test pilots on plenty of airframes), why is there less mentioned that the aircraft may have spun? See my comments above...
Just my two penneth worth...
Unc