[Please see update here.] I don't know Kevin Townsend, though I suspect I'd like him if I did. He's been fighting the good fight against the filibuster, and we have tech and other interests in common. Today he put up a riveting post about a frightening and, in his telling, extremely dangerous episode aboard a recent United flight. The headline gives you the idea:
And he has gotten a lot of pickup for his tale. Eg:
Recently I got my one-zillionth email of the day from a friend or reader asking: What with this, and the Malaysian flight, I'm getting worried. Is something going wrong with our air-safety system?
So in case you're wondering:
- The episode Kevin Townsend describes sounds as if it could have been genuinely frightening, especially to passengers who had no idea what was happening, and he describes it quite vividly.
- On the facts he presents, even though this was frightening, it was nowhere close to as dangerous as it could have seemed. There was no sense whatsoever in which he "almost died."
- Commercial air travel remains remarkable for how extremely safe it is. Even this episode illustrates that reality, since one of many overlapping parts of the air-safety system worked rather than failed.
I wrote to Kevin Townsend a few hours ago to ask some questions
but haven't yet heard back. and have just heard back. Here are the main points to bear in mind.
1) The plane got an anti-collision warning that caused it to descend suddenly, by 600 feet. This is the part that was genuinely frightening to Townsend and other passengers. While in cruise, the United flight crew got a warning from its TCAS, the Traffic Collision Avoidance System, with which airliners and other large planes are in constant automated contact with other aircraft in the vicinity.
If the paths of two airplanes seem likely to intersect, the TCAS in each plane gives each crew a warning. If they are getting too close for comfort, the TCAS gives each of them a "Resolution Advisory" to steer them out of the other's way. One plane will be told to climb, and the other to descend. In keeping with the instrument-flying maxim that you must trust your instruments rather than going by your seat-of-the-pants sense, flight crews are told to trust and follow those TCAS/RA warnings, immediately. The United plane was told to descend right now, and its crew did.
2) How far is a 600-foot descent? This is what Townsend describes as the terror-filled part of the flight:
Weightless and staring downhill at the thirty-some rows of passengers ahead of me, I had a rare and terrible reminder of the absurd improbability of human flight. We were hairless apes crowded into a thin metal tube hurtling through the sky at a speed and height beyond anything evolution prepared us to comprehend. The violence was over after a few seconds. United 1205 leveled out, having dropped at least 600 feet without warning.
Again I am sure this was appalling, especially to people who start out with a fear of being up in the sky. But how far is a 600-foot descent? It is not very far at all. For one thing, it's about equivalent to four plane-lengths of the Boeing 757 that was flying. (That plane is a little over 150 feet long.) If an airliner descended at 600 feet per minute, passengers would probably not even notice it was headed down. If it were descending at what one manual calls a normal rate of 1,800 feet per minute, covering this vertical distance would take 20 seconds. I don't know what the 757's emergency-descent rate is, but if we say it's twice the normal rate that would mean about 10 seconds for getting down 600 feet.