Two Apparent Hypoxia Accidents in One Week


Its never good when a general aviation accident leads the evening news, but that was the case Friday when a TBM 900 became a ghost flight off the South Carolina coast and continued south before crashing in the water off Jamaica early in the afternoon. As we reported, the TBM departed Rochester, New York on Friday morning, bound for Naples, Florida. Absent any other causes, hypoxia is suspected.

With that as the context and this may be my imagination, but I could almost hear every pilot listening to the tapeor reading the transcript and thinking in unison…why arent you declaring an emergency and descending at will? That was my immediate reaction and Im sure Im not alone. Expect to see yet more reminders about the insidious nature of hypoxia and the importance of communicating distress situations unambiguously to ATC and not waiting for permission to act decisively to salvage a bad situation. (There, youve just read one.)

If this accident was due to hypoxia, all we can say is that, fortunately, such things are relatively rare. On the other hand, this is the second such incident in less than a week. We reported last Saturday on a Cirrus SR22 on an IFR flight plan from Waukesha, Wisconsin to Manassas, Virginia that ended in the Atlantic after the pilot became unresponsive. We may never know if it was caused by hypoxia, but that will certainly be an operative theory.

Im not going to drone on with the usual boilerplate about understanding, detecting and responding to hypoxia. In the aviation press, weve done that ad nauseam and the fact that we have finally sunk into my thick skull, causing me to revise my risk assessment of flight-level flying in unpressurized singles and twins. Several things came together to make me disinterested in flying unpressurized above 18,000 feet.

When we initially owned a Mooney 231, I routinely dragged it into the low 20s to try to eke a few extra knots out of it. We had built-in oxygen and I made quite a few flights at FL230, especially east bound during the winter. A 260-knot groundspeed is intoxicating indeed. At the time, we were using pulse oximeters as a safety backstop and on a couple of flights, I was testing these for editorial review. One of them had an alarm feature and now, you can wire these things into panel warning systems. Then it occurred to me one day that I really hated all this crap cluttering the cockpit; I felt more like an intensive care patient than a pilot, all for the sake of a few extra knots. Add the cost of the additional oxygen use at higher altitudes and the entire concept seemed ever sillier.

About the same time, I experienced a turbocharger failure just at the top of climb on the way to Virginia one night. In the high teens, an induction hose popped off the manifold and the MAP dropped from 34 to 18 inches. That got my attention and, as anyone should be in a turbocharged airplane, I was concerned about fire. (I didnt know the failure was on the cold side until I landed.) With fire a worry, I had plenty of time to appreciate how long it takes to get a piston single on the deck from high altitude. Ten to 12 minutes is a lifetime, 20 minutes an eternity. Also, a turbocharged single anywhere in the 20s doesn’t have a lot of surplus performance to climb out of icing or weather turbulence.

The following year, I got an eye-opening demonstration of how rapidly hypoxia can disable a person. In 2006, I participated in the World Team record skydives in Thailand. We were jumping out of C-130s at altitudes between 18,000 and 25,000 feet. I wrote about it for AVweb. On one jump, we were standing on the open ramp at 22,000 feet waiting to exit when one of the skydivers in front of me, a Russian, collapsed and fell back into me. He was stone-cold unconscious and through his face shield, I could see open eyes rolled up into his head like a Zombie. He had used an oxygen hose that had come loose from the feed manifold. He was incapacitated in under two minutes, Id guess.

This confluence of events made me realize that for me, personally, a passive approach to hypoxia avoidance made the most sense. I thought it wise to bake in some hypoxia protection margin by just not going where its likely to be the highest risk in the first place. I stopped flogging the 231 into the 20s, but kept my flights below 18,000 whenever possible. There is a huge difference between hypoxia onset in the high teens and the low 20s and I deemed that the few more knots available for going higher just werent worth that risk. (According to my POH, its 7 knots. Big deal.)

And to be blunt about it, the oxygen systems in light aircraft arent the best, most reliable equipment and the slightest, simplest problem with one might be neither diagnosable nor fixable by even a mildly hypoxic pilot. You might think you can gut it out and descend in time or get the oxygen flowing, but I have a different view, thanks.

Pilots who fly airplanes capable of the flight levels tend to be, in my experience, kind of macho about this. Theyll take the airplane high, confident that theyre prepared and that the risks are tamped down and worth the additional knots. Im not going to second guess anyone on this. As I said, hypoxic incidents seem to be rare. But if I need to fly something into the 20s, I think Ill stick to a Boeing or an Airbus or at least a turboprop, including a TBM by the way. It certainly has the capability to do such a flight safely. But like any mechanical contrivance, its only as reliable as the pilots understanding of its inner workings, not to mention the pilot’s own inner workings. The thin air above 20,000 feet is as unforgiving as it ever was, no matter what airplane is up there.

Join the conversation.
Read others’ comments and add your own.