[zipper]

A few years ago there was a Greek airliner (B-737) climbing out, when a warning horn went off passing about 10,000 feet.

The Captain assumed it was the takeoff warning horn (a malfunction) even though the oxygen masks deployed in the back as they climbed through about 14,000 feet.

The Captain went back to the circuit breaker panel while the first officer flew, and promptly passed out in the floor. The copilot continued the climb and eventually passed out at the controls.

The airplane flew for couple of more hours — eventually a flight attendant got in the cockpit (the intrusion resistant door was locked) who had some training in light aircraft.

The flight attendant couldn’t figure out how to operate the radios but flew it for a while until one engine flamed out due to fuel starvation and the airplane spiraled down into the ground.

Turns out the outflow valve was fully open the whole flight, preventing the airplane from pressurizing, because the Captain missed it on his cockpit setup.

Hypoxia is very serious and as you probably know any airplane with a cabin pressure above 10,000 feet must have supplemental oxygen. Most airliners cruise with a cabin altitude of around 8,000 feet.

But at 50,000 feet and up, where the Raptors like to be, the cabin pressure is likely to be closer to 25,000 feet, which is the altitude limit for unpressurized aircraft with supplemental oxygen. At those cabin altitudes hypoxia is more sudden and supplemental oxygen is a must under normal conditions, not to mention if there were a sudden loss of pressurization.

http://www.nytimes.com/2005/09/06/world/europe/06iht-crash.html

[USNBandit]

I used to fly maintenance profiles for two of the types of aircraft I flew. At 45,000 feet the cabin pressure is 18,000. Fortunately, my chamber rides every 4 years prepared me well for the couple times that I had cabin pressure malfunctions in flight. Both times, my pressurization had slowly failed. Each time I had popped my mask to take a break from sucking rubber and immediately felt the effects. The first thing I did each time was slap that mask right back on and go to 100%. Then I started looking to figure out what was going wrong.

The problem with OBOGS is that sometimes you don't have any warning. I had a good friend put on his mask in an OBOGS equipped hornet as he took the runway. As the aircraft rotated he could tell something was wrong then he lost his sight. He remembers fumbling for his emergency O2 bottle in his seat that cut off the OBOGS and provides bottled oxygen. He regained his sight passing 3000 ft AGL and 350 knots with the gear still down (slight overspeed there). He almost got killed.