Originally Posted by M.Mouse
So how do you answer AirRabbit's conjecture that the B737 characteristic for alarming and uncontrollable behaviour with leading edge contamination possibly occurred and all that greater thrust would have achieved would have been that the aircraft and its occupants would have reached the point where the tragedy was inevitable marginally quicker?
How could I possibly answer that? I am not an aerodynamicist familiar with 732. Heck, I'm not even rated on her, but I can easily find an expert opinion on the matter:
Originally Posted by NTSB AAR82-08, page 54
The Safety Board concludes that neither the low thrust used during the takeoff
nor the presence of snow or ice on the aircraft, alone, would likely have led to the crash.
In most other reported incidents in which B-737’s have pitched up during takeoff, the
flightcrews had sufficient control authority with forward control column force and
stabilizer trim to overcome the pitching moment, reduce the pitch attitude, accelerate
to a lower angle of attack, and climb out successfully. The Safety Board believes that if
the proper thrust level (that for 2.04 EPR) had been used for the takeoff this flightcrew
could have recovered from any difficulties caused by the contamination - induced
aerodynamic performance penalties.
Furthermore, based upon the engineering simulation, the Safety Board
concludes that even with the low thrust during the takeoff roll and the aerodynamic
penalty of the snow or ice contamination, the accident was not inevitable as the aircraft
lifted off. However, both immediate recognition of the situation and positive effective
actions by the flightcrew to both counter the noseup pitching moment and add thrust were
required. With these actions, the aircraft should have been capable of continued
acceleration and achieved a sufficient performance margin for climbout.
Originally Posted by NTSB AAR82-08, page 68
The engineering simulation of Flight 90’s flight profile disclosed that the aircraft’s rate of acceleration after liftoff, below normal
because of the reduced thrust, was further impaired by a high noseup pitch attitude attained during the takeoff rotation.
Consequently, the aircraft did not reach an airspeed
safely above the stall speed. The high pitch attitude occurred because the flightcrew
failed to, or was unable to, react quickly enough to counter the aircraft’s longitudinal trim
change produced by the wing leading edge contamination. The reports since 1970 by other
operators who have experienced abrupt pitchup or rol off immediately after liftoff of
B-737 aircraft indicate that the B-737 may have a greater known inherent pitchup
characteristic than other aircraft in this regard a result of small amounts of frost, snow,
or ice on the wing leading edge. The Safety Board could not determine whether the
aerodynamic design makes the B-737 more sensitive to pitching or rolling moments when
the wing is contaminated, or whether more frequent operation of these aircraft in
environmental conditions conducive to snow or ice accretion during ground operations,
coupled with the near to the ground wing placement, accounts for the higher number of
reported B-737 pitchup/rolloff incidents, Regardless, the Safety Board concludes that the
pitchup tendency of the aircraft because of leading edge contamination contributed to the
accident. However, to place this contributing factor in perspective, the Board notes that no
aircraft design requirements include the ability to perform with snow or ice
contamination and that any known contamination, regardless of the amount or depth, must
be viewed as potentially critical to a successful takeoff. For this reason, flightcrews are
not only dissuaded, but are prohibited, from attempting a takeoff with such
contamination.
Hope this helps. The report goes into great detail how the conclusions were made.
So how come some PPRuNers get convinced by the theories that are at odds with the expert analysis and have no traceable source? PukinDog nicely analyzed one such contribution:
Originally Posted by Pukin Dog
You make decent enough arguments on a few points, food for thought anway, but wrapping them in a suggestion that this crew's actions and words represent anything like a barometer of "what was known", done, and disseminated (including to them) re winter ops/contamination/ etc 1982 is a gross misrepresentation. This crew was nothing of the kind, and you whitewashing this crew's inexperience and non-compliance for the sake of focusing on the de-icing issue hints of an agenda.
The picture certain poster has painted has some true details, some true yet grotesquely exaggerated, some completely irrelevant, some that are so-pulled-out-of-the-thin-air they cannot be verified at all and some brazenly false. When the details are put together the composition reveals what was the message (original term was "the truth") that the contributor wanted to get through: the poor, hapless crew was tragically betrayed by almost everyone. They were betrayed by the de-icing crew that poured water instead of glycol mixture on their wing. They were betrayed by FAA by not having developed the holdover times at the time. They were betrayed by the Boeing co designing the aeroplane that would pitch-up when stalling with iced leading edge. They were betrayed by the ATCO using too little spacing between them and landing Eastern. Basically, it was everyone else's fault, they were just the one who died. There was nothing they could do. They were doomed.
Realistic picture, eh? Not at all. So how come it is believable? Basic HF: people are convinced of something because they want to be convinced. If reading the accident report pages where crew's mistakes are neatly explained fills you with horror and, despite the facts, you want to believe that QH90 (or any other) crew did their best but it was tragically insufficient, to sooth your anxiety you would do well to listen to alternative theories of e.g: de-icing with water, composite fins being weaker than metal ones or Airbus cockpit being a deathtrap by design.
However, if you are into learning something from mistakes of others, lest you repeat them, it's far better to read and understand what is written in the official accident report. Stress is on understanding as it will help you recognize skewed reports produced under undue political pressure or when the good report is unduly smeared as false.
Whatever suits you, terms of the PPRuNe use do not preclude going whichever path you choose. Outcomes might differ, though.