Regarding the initial sudden climb:
"'The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs. The vertical speed, which had reached 7,000 ft/min, dropped to 700 ft/min and the roll varied between 12 degrees right and 10 degrees left. The speed displayed on the left side increased sharply to 215 kt (Mach 0.68). The airplane was then at an altitude of about 37,500 ft and the recorded angle of attack was around 4 degrees."
So obviously to some extent the aircraft was climbing despite the pilot's attempts to lower the nose. Keep in mind that with a whale of a plane like this, there is a lot of inertia. It is not a maneuverable fighter jet.
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On the question of using GPS as a substitute for pitot tubes - here's why it isn't useful (apologies to the 98% of pilots who already know this), especially at 35,000 ft.
The behavior of an aircraft is determined by effective or INDICATED airspeed. How much air is flowing over the airfoils and controls.
An aircraft at 35,000 feet flying at 500 kts, may show an indicated (pitot) airspeed of about 260 kts (depends on temperature) - because the air is so thin. More importantly, it will BEHAVE as though it is only going 260 kts, because there are fewer air molecules to hold up the wings or have an effect on the control surfaces.
The "magic" of the pitot system is that it measures the EFFECTIVE airflow at any given altitude, thereby fairly accurately reflecting how the plane will handle as the air gets thinner. (At least up to the point where Mach effects kick in - getting close to the speed of sound introduces its own issues.)
A GPS cannot do this. It only reports how fast the plane is actually moving, which says nothing directly about how much airflow the pilot has to work with. In addition, it figures in wind effects, which also have no direct usefulness in controlling the plane.
Pop quiz:
You are at 35,000 feet. The GPS says you are traveling at 400 kts due north over the ground, decreasing at 1 kt per second. There is a 60-kt jet stream blowing from the southwest (217°). Your stall speed (no flaps) would be 167 kts INDICATED, but your airspeed indicator isn't working. Your heading is 356°. Barometric pressure is 29.75 (but your altimeter is set to 29.92 as in all flights above 18,000 feet.) The air outside is -42° C.
Tell me how close you are to a stall. (You have 10 seconds to calculate this).
Doesn't work.
The reason planes still use a 160-year-old instrument for airspeed is that it remains the best tool for the job.
Last edited by pattern_is_full; 29th May 2011 at 19:25.