Friday, May 27, 2011
Sleeping in Coffin Corner
(1)
First sip at 1627. I'm a bit late this week, but I have been doing 'blog prep' today instead of playing C-III.
I should probably do this part (Air France crash) of the 'rink dump' while I'm still sober enough to make sense. (Buzzing slightly at 1643.) Apparently the airplane flew through heavy icing conditions just before the crash: The icing was so heavy that it overwhelmed all of the heated pitot tube sensors causing them to malfunction. The wing and tail leading edges would also have quickly accumulated huge amounts of ice unless deicing systems had been activated. Lacking enough information to properly manage the airplane, Mister Autopilot submitted his resignation, waking the pilots up unexpectedly. They began to analyze the situation. One of the pilots, perhaps fearing they were losing altitude, pulled back on the stick (we saw this reaction in another fairly recent crash involving icing). The airplane stalled as a result, and began settling rapidly. The pilots were apparently oblivious of the stalled condition, and did not 'lower the nose' to gain airspeed. The stalled airplane descended rapidly (about 10,000 feet per minute), wallowing left and right. One of the pilots decided to wake up the chief pilot for advice. The other pilot continued to 'analyze the situation.' The (previously sound asleep) chief pilot awakened with, 'Whas up?' (or perhaps the French equivalent thereof). He got right to work, but was still in 'wake-up mode' at the time they hit the water a minute later.
That's my irreverent version, at least. Most folks don't know that modern jets at high altitude are flying in the vicinity of 'Coffin Corner.' They call it 'coffin corner' because in the thin air at high altitude the airplane must be flown at high speed with a high 'angle of attack' (very fast and very 'nose up'). The result is that the airplane is close to both the 'stall buffet' and the 'speed buffet' and must be flown very carefully. Too fast and the horizontal tail surfaces will begin to vibrate and the airplane could disintegrate. Too slow and the airplane could stall (or better, descend). (For a more sophisticated description of 'coffin corner' see here.)
First sip at 1627. I'm a bit late this week, but I have been doing 'blog prep' today instead of playing C-III.
I should probably do this part (Air France crash) of the 'rink dump' while I'm still sober enough to make sense. (Buzzing slightly at 1643.) Apparently the airplane flew through heavy icing conditions just before the crash: The icing was so heavy that it overwhelmed all of the heated pitot tube sensors causing them to malfunction. The wing and tail leading edges would also have quickly accumulated huge amounts of ice unless deicing systems had been activated. Lacking enough information to properly manage the airplane, Mister Autopilot submitted his resignation, waking the pilots up unexpectedly. They began to analyze the situation. One of the pilots, perhaps fearing they were losing altitude, pulled back on the stick (we saw this reaction in another fairly recent crash involving icing). The airplane stalled as a result, and began settling rapidly. The pilots were apparently oblivious of the stalled condition, and did not 'lower the nose' to gain airspeed. The stalled airplane descended rapidly (about 10,000 feet per minute), wallowing left and right. One of the pilots decided to wake up the chief pilot for advice. The other pilot continued to 'analyze the situation.' The (previously sound asleep) chief pilot awakened with, 'Whas up?' (or perhaps the French equivalent thereof). He got right to work, but was still in 'wake-up mode' at the time they hit the water a minute later.
That's my irreverent version, at least. Most folks don't know that modern jets at high altitude are flying in the vicinity of 'Coffin Corner.' They call it 'coffin corner' because in the thin air at high altitude the airplane must be flown at high speed with a high 'angle of attack' (very fast and very 'nose up'). The result is that the airplane is close to both the 'stall buffet' and the 'speed buffet' and must be flown very carefully. Too fast and the horizontal tail surfaces will begin to vibrate and the airplane could disintegrate. Too slow and the airplane could stall (or better, descend). (For a more sophisticated description of 'coffin corner' see here.)
