Soaring at altitudes that could have reached 51,000 feet, its cockpit windows apparently frosted with ice, the jet continued for nearly four hours. Along the way, the Learjet was shadowed by military fighter jets, whose pilots attempted to peer inside and learn what was happening. Air traffic controllers cleared all other planes from the Learjet's path. Investigators still had not examined the wreckage late Monday, but aviation experts and government officials say that initial evidence suggests that the pilots could have been overcome by lack of oxygen after the cabin somehow lost pressure. The air is so thin and cold at 40,000 feet and above that people lose consciousness within seconds, they say.
Dust flies up, and all the moisture in the air immediately vaporizes.
The rapid change in pressure and falling temperatures create a thick fog that can obscure people's hands in front of their faces. It also leaves frost on an aircraft's windshield. But this scenario of the Learjet's fate raises many conflicting questions. Pilots are tested and retested on their ability to apply oxygen masks quickly and descend if pressure is lost. The reaction to that is as instinctive as pulling your hand away from a hot stove.