A friend of mine got an aerial mapping job last summer. He had to fly at
twenty thousand feet to take the pictures. Some pilots can stand more
altitude than others, but my friend didn't know how much he could stand
because he had never flown that high. He decided he had better take
oxygen with him, just in case.
His mechanic got a cylinder of oxygen for him, and he took off. He felt
pretty groggy at eighteen thousand feet, reached down, got the hose, put
it in his mouth, turned on the valve, and took a whiff of oxygen. He
couldn't hear the hissing of the stuff escaping because the motor noise
drowned it out.
He perked up immediately. The sky brightened, everything became clearer
to him, and he went on up to twenty thousand feet. Every once in a while
he would feel low and reach down and get himself another whiff of oxygen
and feel all right again for a while.
He didn't say anything to his mechanic, but his mechanic decided for
himself a few days later that the oxygen was probably getting low in
that tank and that he would need another soon. He decided to put a new
one in ahead of time to forestall the possibility of running completely
out in the air.
He brought a new tank out and decided to test it before he put it in the
ship. He opened the valve and nothing happened. The tank was empty.
He took it back to the hangar and discovered that the previous tank my
friend had been flying on had come out of the same bin and had been
empty all along.
He got a good one and put it in the ship and didn't say anything about
the incident. My friend said that the next time he took a whiff of
oxygen it almost knocked him out of his seat.