A U.S. physiological technician on-board a C-17 Globemaster III ensures that crew members do not succumb to hypoxia.Reuters

No one knows the cause of the latest airline disaster, the Germanwings crash yesterday in Southern France. As is usually the case after crashes, most first-day speculation is wrong or implausible. Also as is usually the case, Patrick Smith of AskThePilot has debunked many of the most fanciful cable-news theories, for instance that the plane might somehow have been remotely controlled, like a drone, or victim of "hacking" of its flight software. Without getting into all the details, this is vanishingly unlikely to have been the cause, and is so far-fetched as to merit no on-air discussion time.

The main fact that is now established is that the airplane flew steadily along its course, descending at a faster-than-normal but not-necessarily-emergency rate of 4,000 feet per minute, until it flew right into a mountainside. This is the scenario known in aviation as Controlled Flight Into Terrain, or CFIT, and it usually occurs at night or in the clouds when a flight crew does not realize what it is about to hit. It is different from what you would expect if the plane had broken apart or suffered some other major structural or control failure while aloft.

The long, controlled flight path to disaster, combined with the reported absence of any radio transmission from the crew, would be consistent with the flight crew somehow being incapacitated and unable to control the plane. This scenario would involve:

    a) something very bad happening very suddenly, like an explosive decompression or an electric fire that filled the cockpit with smoke;

    b) the flight crew quickly dialing an expedited-descent rate into the autopilot (but not setting a minimum altitude at which to stop the descent); and then

    c) the flight crew, for whatever reason, being disabled very soon afterwards, before they could level off at a safe altitude, adjust the autopilot's flight path to turn away from the mountains, or even make a radio call. This would also be consistent with their not switching the transponder, which emits a four-digit code identifying each flight, to the 7700 code for "Emergency." The flying world's mantra for priorities during an emergency is: Aviate, Navigate, Communicate, in that order. So trying to get the plane down to a safer altitude would have come before bothering to make any radio calls.

Whether any of this happened, and why, is what a Cockpit Voice Recorder should eventually clarify, since the members of the crew would have been talking with each other even if they were not making radio calls. Until that is known, here is a dramatic illustration of how powerful and strangely undetectable the effects of hypoxia—lack of oxygen—can be.  

Here is another disturbing one, "Four of Spades," which again conveys how limited oxygen can destroy reasoning power without the victim's being aware of it.

Back in the 1980s, I went through this pressure-chamber training before taking a flight (which I described in this magazine) in an Air Force F-15. The process was slightly different from what's shown in these videos: As the oxygen level went down, I was told to keep writing words and doing simple arithmetic problems on a little paper pad. When it was over, I looked at the pad and could barely understand any of the letters. I could, though, see that I had been unable to solve the math problem of 3 + 4.

Sympathies to all affected, and I hope at least the mystery of what happened can be solved soon.

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