If you've ever been troubled by doubts about the plausibility of Dorothy's being carried off in her house by a tornado and then dumped back on the ground, house and all, without injury to herself or Toto, an accident that took place a few years ago should persuade you that it really could have happened.
A Cessna 337D Skymaster, an unpressurized, turbocharged twin modified with a floor-mounted camera in the cabin, departed its home base in order to do some aerial photography. The 3,100-hour private pilot and his assistant were aboard. After shooting three locations, they landed at another airport. There the pilot filed an IFR flight plan and "set up" the portable oxygen system, which had been charged that morning, for the next flight. This time, they would be climbing to 25,000 feet.
They took off at a quarter to two. As they climbed through 10,000 feet, the pilot told his assistant to put her oxygen mask on. He did the same. The assistant tried to turn on the oxygen but wasn't sure how, and the pilot reached back to open the valve. The assistant knew the oxygen was now on, because she could feel cool air flowing into the mask and the flow indicator ring in the oxygen line changed from red to green.
As the Skymaster climbed through 20,000 feet, the pilot remarked on the altitude and asked the assistant how she was doing and whether she felt OK. She said she did. Then, however, she became aware that she was starting to feel dizzy and was having trouble focusing. She felt as though she were cross-eyed. She said to the pilot that she was feeling dizzy, but he didn't respond. He must be talking to the tower, she thought. She closed her eyes and noticed that this made her feel better.
Air Traffic Control had cleared the flight to maintain FL 250. Controllers, unable to communicate with the pilot, observed the airplane climbing through that altitude, eventually reaching 27,700 feet. It then descended to 26,000 feet before radar contact was lost.
Shortly afterward, the airplane rained down in pieces over an area of several square miles. Both tail booms, together with the empennage, outboard left wing and the right door, had separated from the cabin, which fluttered down with its two occupants. It came to rest 30 feet above the ground in a hickory tree. The pilot was dead, not from the impact but from lack of oxygen. His assistant, however, was merely unconscious. Perhaps profiting from the divine protection allegedly accorded to some who collide with doors, stairs and lampposts while in states of impaired consciousness, she sustained only cuts and bruises in the crash.
The weather at the time of the accident was good, and there was no indication of any mechanical malfunction. Investigators tested the gas in the FBO's oxygen bottle from which the portable unit had been filled, and found it to be not pure oxygen but, instead, simply compressed air. It appeared that, because of some misunderstanding between the FBO and his oxygen supplier, the FBO had been regularly receiving, and dispensing, compressed air in the belief that it was aviator's breathing oxygen.
A bottle of compressed air is useful at sea level (for breathing in toxic environments, for example) and under water, but it is of no use at all at high altitude, because once the air emerges from the bottle it is at ambient pressure and is no different, for breathing purposes, from the ambient air.