Hey Barit1 – Thanks for the comment.
Believe me, I KNOW what the NTSB report says. But what it doesn’t say is that on the same day, (actually it was about 8 hours earlier) half-way around the world in Scandinavia, another B737 was subjected to a rather fierce snow/freezing rain scenario while taxiing out and awaiting takeoff clearance. As the crew initiated the takeoff and brought the control column “to neutral or slightly aft of neutral to prepare for the rotation” (quote from the Boeing manual), that B737 auto-rotated just like the B737 in Washington. However, because this airplane was subjected to a crosswind, the deformation on the wings was asymmetrical. The airplane pitched up to about the same pitch attitude as in Washington (in the neighborhood of 22-23 degrees) but because of the asymmetrical deformation, the pitch was asymmetrical as well, and resulted in a pitch up and roll off. The crew had the control column against the forward stops. They slammed the throttles to the firewall, went to full opposite aileron, full opposite rudder – to no avail. They were along for the ride. However, as the roll continued over toward 90-degrees, the nose began to fall. As the nose began to come down toward the horizon, the airplane began to accelerate. As it accelerated, the outboard portion of the affected wing began to produce lift and the aileron became effective. The crew rolled level less than 100 feet above the ground. When advised of the existence of this circumstance, the NTSB chose not to look into it.
As for why doesn’t this happen more often … Well, the Washington accident airplane was deiced – but it was deiced with hot water – sprayed very evenly over the entire airplane, which promptly froze in the 22-degree weather. There was a malfunction in the Trump De-icing Truck and the ground crew made improper repairs that resulted in drawing only from the water tank when spraying anything above the “ON” position dribble out of the nozzle. So, this circumstance is not seen very often because not very many airplanes are deiced with water – carefully, all over the airplane, with particular attention given to the lifting surfaces, when its way below freezing outside!
As you would probably guess there was a flurry (no pun intended) of lawsuits filed and everyone was pointing fingers at what “came out” during the NTSB public hearings. It was interesting when some found out that during the flight-testing of the B737, Boeing had recorded several instances of a “pitch up” or a “pitch-up/roll-off” occurring during periods of freezing precipitation (snow/freezing rain primarily). In these situations the test pilot indicated that the airplane was not controllable, and it was all written off as “autopilot anomalies.” This, in combination with the revelation that Boeing had been working on the development of an anti-icing/deicing system to be used during takeoff for the B737, led to the fact that the settlements reached were split between the operator’s insurance company and Boeing. The NTSB report acknowledges “the known, inherent pitch-up and roll-off tendency of the B737” but attached no particular importance to it.
I know that the report cites the PT2 probes as being iced over. I also believe that to be the case. But the power setting is not what gets an airplane into the air. Flight crews rotate when they get to the previously computed rotate airspeed. It is airspeed that allows the airplane to fly. It is airspeed, or lack thereof, that causes an airplane to stall. In fact, given that the takeoff would have been somewhat longer with only 75% power from both engines from initiation of the takeoff roll, it still should have achieved flight and certainly should have been able to sustain flight – it had 50% more power than with what the airplane had been certificated to operate. The problem is that if only the inboard portion of the wing will generate lift or it generates substantially more lift than the outboard portion of the wing, when the forward control column pressure is relaxed, the inboard (forward) portion of the wing acts just like it should – and the outboard (aft) portion does as well. The result is a pitch up – and if it is asymmetrical, you get a roll as well.
I’ve had the opportunity to make several “simulated single engine” takeoffs in DC-9 aircraft (not the simulator), from initiation of takeoff roll, using one engine at idle power and the other at takeoff power. The throttle has to be advanced slowly and steadily while maintaining a good grip on the NWS until the rudder becomes effective. Yes, the takeoff roll is longer, but it got into the air every time.
There are other “interesting” factors about the NTSB report that I could go into, but I’ve probably already said more than enough to satisfy anyone who was confused about what really happened that day in January 1982.
Let me know if you “want more” -- because there certainly is more…
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AirRabbit
Last edited by AirRabbit; 27th Sep 2005 at 02:36.