Friday, July 29, 2011

For Want Of A Nail

I have a fascination with the last irretrievable moment. In every accident, in every major event, there's almost always a definable moment where disaster could have been averted. If only key people had had one key piece of information, if only they'd made one decision differently, everything could have been different.

There was one such moment during the last tragic mission of Columbia. If the manager in charge had pushed for satellite images of the shuttle's underside, the extent of the damage might have been known, and it might have been possible to mount a rescue effort. There's a lot of mights involved ... but we also might have gotten those seven people back alive. And we might be seeing one now, in Washington. But that's not the one I'm talking about today.

On the first of June, 2009, Air France Flight 447 disappeared over the Atlantic Ocean. Its automatic systems had blurted out signals of danger, and then, silence. At the time, I had speculated about what might have gone wrong. Speculation was all it amounted to. Without the flight data recorders, no one would ever know the truth of the matter, and the data recorders were buried under eleven thousand feet of ocean. I fully expected no one would ever see them again.

I vastly underestimated the tenacity of France's Bureau of Investigation and Analysis. In May 2010, they had narrowed the location down to a five by five kilometer area. That gave them a small enough zone to allow a team from the Woods Hole Oceanographic Institute to make a more detailed search. In April of this year, they found the wreckage, and with it not only the flight data recorder, but also the cockpit voice recorder. If that wasn't amazing enough, they were able to recover all of the data from both devices. Truly, this was astounding work, and my hat's off to them.

Now, after sifting through the reams of data available to them, the BEA has issued some preliminary reports. It turns out that some of my initial speculations were right, some less so.

The data clearly tells us that the pitot probes had iced over, corrupting the data going into the air data computers. This meant that the data feeding the primary flight displays weren't any good. What's not clear to me yet is exactly what happened next. They don't say if an updraft lifted the nose of the aircraft, or if the ice on the aircraft caused it to slow to a dangerously low speed. I'm guessing the latter, because they say that the crew pulled the nose of the aircraft up, which they probably wouldn't have done if the aircraft was already nose-high. The main point is, the aircraft was already on the verge of a stall, and lifting the nose made a bad problem worse. The aircraft then simply fell out of the sky.

The preliminary report released today says that it's basically a pilot training problem. Pilots typically have little to no training flying an aircraft manually at that speed and altitude, and therefore have little intuition on how they should recover from a situation like this. The BEA recommendation is to add this condition to the pilot training syllabus.

After thinking about it a bit, I have a few observations of my own.

1) Standby instruments rarely get the respect they deserve. Ideally, your cockpit scan should include your standby instruments, especially in a glass-cockpit airplane. If your air data computers are hosed for whatever reason, your standby instruments may still have good information on what your airplane's doing. If your standby instruments don't agree with your primary displays, you've got a problem. Exactly what kind of problem you won't know, but at least you can start looking. This particular failure cascade seems to indicate that the crew were still flying by the primary displays, up to the point where they no longer had any aerodynamic control. Respect your ISIS, ladies and gents, that's what it's there for.

2) Airbus makes an exceptionally sturdy fuselage. Really, this could apply to any modern composite-structure fuselage. They're absurdly strong. From the initial reports, I expected that the aircraft would have broken up in midair from aerodynamic stresses. A mostly aluminum structure probably would have. But from the wreckage, we know that it was intact when it hit the water. It was doing some pretty serious gyrations on the way down, and didn't come apart. That's solid construction.

3) These days, we can find damn near anything, damn near anywhere. I was sure those recorders were gone forever. Fish food, if there are any fish that live two miles down. Apparently, modern sonar is as good as a searchlight. I don't know exactly how those French submarines were able to narrow the field down as close as they did, and for obvious reasons they're not telling. But it's clear that if they want something found on the ocean floor, it can be found. And that wasn't a guarantee ten, or even five years ago.

4) There's a good reason for all this, besides morbid curiosity. The reason people like me pick disasters apart like this isn't that we're morbid toads. We may be, but that's beside the point. We want to know what happened, and how it happened, so we can stop it from happening next time. If that's even possible. The important lesson to come out of all this is that we've uncovered a gap in pilot training. We have the means at our disposal to close that gap. Thirty minutes of simulator time a year, and a pilot will have "experienced" this situation with enough fidelity that he or she will know what to do if the real thing ever happens. The next time this happens we'll probably never hear about it. The passengers will experience a bout of worse than normal turbulence, the pilots will experience five minutes of bowel-freezing terror, but the airplane will arrive at its scheduled destination. We'd have not known this, if we'd let it alone. Poking and prodding is part of our job. Our duty. Not always the most pleasant part, but an essential part nonetheless.

It's not much consolation for the people who lost loved ones two years ago, but this knowledge, painfully gained, may allow us to save the next one. That's certainly worth something.

Dedicated to the memory of Dr. Don Seath, my first professor in Aerospace Engineering, who passed away in May from pancreatic cancer. You taught me well.


John Myste said...

A very wise man once said: I have a fascination with the last irretrievable moment. In every accident, in every major event, there's almost always a definable moment where disaster could have been averted.

That is a fascinating idea. What would you speculate was such a moment in the "debt crisis?" Our credit rating is now down graded. The DOW is jumping off a cliff, and the general mood is grim.

Where is the moment?

John Myste said...

Poking and prodding is part of our job. Our duty.

You have a freaky knowledge of physics, et. al. What exactly do you do and how do you know all this stuff?

I replaced a faucet the other day and it taxed my abilities to their limit.

Tim McGaha said...

In reverse order:

I never talk about my employer, or about exactly what my "day job" is. That's partly due to non-disclosure agreements, and partly due to the fact that such talk is unprofessional. But I can say that my background includes most of a doctorate in Aerospace Engineering, two years as an Air Force ROTC cadet, a lot of practical experience as a software engineer, and a short stint as a student pilot. I'm a little unusual amongst engineers in that I don't hate writing.

As to our current mess: I thInk the last, best opportunity was the so-called "grand bargain", which the Tea Party dismissed out of hand. But, it's not yet sailed off the cliff. S&P downgraded, but so far no one else has followed suit. If there's serious movement on our long-term structural problems, we may yet muddle through. It could be a rough ride, though.