By now many of you have heard the ATC tapes for the TBM 900 that kept flying long after the pilot was unresponsive , eventually crashing near Jamaica. If you haven't heard them, I can't suggest that you listen. They're hard to take, knowing as we do how the flight ended. At the same time, it's important to understand the nature of hypoxia, the way it creeps up on you and before you can act decisively, you've lost the ability to act decisively. Anyone who's seen a demonstration of an altitude chamber has seen the hilarious attempts pilots deprived of sufficient oxygen make when trying to perform simple tasks, like writing their name, and the surprising lack of awareness they have of the level of impairment they are suffering.

Unfortunately, in real life, hypoxia is dead serious. There are only a handful of hypoxia-related accidents that take place every few years, but the other week we were witness to a couple that are examples of what happens.

The first, the case of a Cirrus SR22 whose 67-year-old pilot became unresponsive , ended in tragedy as well, though it might not have been hypoxia, as some have speculated. That airplane, which crashed in the Atlantic east of Virginia, has not been recovered and likely never will be. It is not known if the pilot suffered hypoxia or some other unrelated health condition. Flying at an altitude of 13,000 feet, the pilot was not at great risk of severe hypoxia, but it is a possibility.

The second accident, which happened last Friday, that of the TBM I mention above, is perhaps even more striking, as it seems a textbook illustration of the insidious nature of oxygen deprivation, even in a pressurized airplane flown by an experienced pilot.

I fly at Oxygen altitudes all the time in my Cirrus, though seldom above 18,000 feet, the level at which one is required to wear a mask and not just a cannula. I do what I can to safeguard the process. I have a pulse/oximeter I keep on a little ledge just below the MFD in the Cirrus. I use it to check my O2 and pulse every few minutes. I'm a bit obsessive about it, even though at 16,000 or 17,000 feet, the risk I'm taking is not relatively as great as it would be at a higher altitude. I am a distance runner who is in very good condition, and in the mid-teens, the risk to someone like me of passing out is low. Also, I should note that the ESP System in my Cirrus would fly me down to 10,000 feet if I became unresponsive and fly along at that altitude until I came to, not that I plan on that as a contingency.

My strategy simply is to keep a very careful eye on my oxygen levels and if necessary, immediately descend to an altitude where I wouldn't need supplemental oxygen.

Does this strategy guarantee my safety? It doesn't. But it's a far better approach than not paying attention; flying much higher and having the optimistic point of view that everything will simply be all right.

Finally, while the investigation into what happened with that fateful TBM flight is just getting under way I have to stress how important it is to not take ATC's word for law when there's an emergency or near-emergency brewing.

Controllers are often ignorant of the special needs of light planes flying in the flight levels, and we need to make them aware of them. If you suspect for one second a malfunction of the oxygen system, don the masks immediately (in a pressurized airplane); commence an emergency descent while notifying ATC when you can. Declare an emergency without any regard for the regulatory consequences. FAA paperwork sucks. The alternative is infinitely worse.

And remember, oxygen deprivation creeps up on you. Don't try to think through the emergency. You might not be able to. Descend, descend, descend. Then think about it all you want.

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