Monday, January 19, 2009

Miracle on 45th Street: Role of the Engineers

What could have been a tragic airplane crash that killed over 150 people turned last Thursday into one of those rarities, a big news story with a happy ending. When Pilot Chesley Sullenberger mentioned a minute into his flight out of New York's La Guardia Airport that he was seeing a lot of birds, he probably didn't think that a few seconds later, both of his engines on the dual-engine Airbus A320 would flame out simultaneously. But the flight data recorder shows that is exactly what happened once the plane reached an altitude of 3,200 feet.

We don't know for sure if it was birds that caused the accident, but what we do know is that everything happening after that had years of skilled professional and engineering planning behind it. Sullenberger, as it happened, had made a study of how cockpit crews react to emergencies, and was planning after retirement to start an airline-safety consulting business. I would say that his chances of succeeding in that business are greatly improved after what happened next. By all reports, he calmly steered the aircraft down the center of the Hudson River, got on the PA system to the passengers to say only one thing: "Brace for impact," and splash-landed the craft intact, unless you count the loss of one engine, which was not doing him any good at that point anyway. Although there were isolated cases of panic on the part of the passengers, the plane remained afloat long enough for everyone—100%—to get out alive and reasonably well. Some people even went back to the airport and continued on their travels right away.

The word "miracle" is being used a lot to describe what happened. I will not argue with that. If you had asked me what the chances of survival were on a flight that lost power less than a mile above the Hudson River, I would not have given you very good odds. Over my years of airline travel, I have watched dozens of times as flight attendants went through the FAA-required safety lecture, complete with gestures involving seat belts and those improbable-looking life vests that they never actually inflate. I had come to regard the whole thing as a kind of ceremony done not for any practical consequences it might have, but merely to make the passengers feel better. Listening to them talk about inflating the vest by blowing into the mouthpiece and so on usually reminded me of an alternative version an irreverent colleague once told me: "In case of emergency, put your head down between your knees and kiss your a-- goodbye."

But the miracle of flight 1549 makes me rethink these cynical musings. It is indeed possible to splash-land a commercial airliner in such a way that if it happens to come down in the middle of one of the most rescue-ready waterways in the world, all the passengers and crew members can get out safely. I have been unable to discover how deep the water was at the crash site, but it was apparently too deep to support the plane, which nevertheless floated long enough for a successful rescue operation.

The fact that it did so, and that it didn't break up on impact, and that the engines didn't set the whole plane on fire after they failed, and a number of other fortunate occurrences that I am not technically savvy enough to imagine, is due not only to the grace of God, and the skill of the pilot and co-pilot, but to the planning, experience, and wisdom of the engineers who designed and built the A320 Airbus. Not every kind of aircraft could withstand that sort of abuse, but this one did. The survival of the passengers depended on the integrity of the airframe, which came through with flying colors (or floating, as the case may be).

Perhaps it is petty to quibble about a minor point, but the only thing that would make this good story better would be to discover that there were actually enough life rafts on the plane to accommodate all the passengers. I don't know whether there were or not. Now in the case of a 747 or something equally large, I don't think surviving a water landing is feasible. The stresses on such a structure would simply be too great, and even if you packed enough life rafts for the over 350 passengers, there might not be any room left for luggage. But after Sullenberger's triumph, we should at least give some thought to the question of how to survive a similar splash landing in the open sea.

In the early days of commercial air travel, many if not most intercontinental flights used "flying boats" intentionally designed to land on water. The reliability of reciprocating engines was simply not that great, and it was probably a good public relations move for airlines such as Pan Am to be able to reassure the public that even if all the engines failed (and there were usually four), there was at least a chance of landing safely on the water, whereupon the plane would float indefinitely. Once engine reliability improved, the flying boats gradually disappeared, although there are a few left for specialty purposes. It turns out that water landings have their own hazards, so the increased safety of water-landing aircraft is more apparent than real.

But the good news coming out of the Hudson River last Thursday was real, and I hope this incident enters the engineering ethics literature as a good example of things going right. It is fully as exciting a story as many less fortunate technical mishaps, and has a happy ending. One of my colleagues used to summarize his goals in teaching engineering ethics as "No headlines." Generally that is good advice, but the headlines about the miracle on 45th Street, near the Manhattan shore where the plane landed, were welcome news indeed, for engineers and for everyone else.

Sources: I drew upon several news reports for this column, including a New York Daily News item at and a Yahoo News item at, which carried information about the flight data recorder.

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