Monday, November 16, 2009

Air Accidents In Perspective

A good fraction of classic engineering-ethics cases are concerned with accidents involving air transport of some kind, with commercial airline traffic taking the lead in terms of fatalities involving members of the public (as opposed to astronauts, for example). For example, in the early 1970s, problems with a DC-10 cargo door latch led to one near-fatal accident, halfhearted attempts to remedy the problem, and then a serious crash in France on Mar. 3, 1974, that killed 346 people. This case is held up to generations of engineers as an example of how not to fix a mechanical flaw in a life-critical system.

Although we have dealt with individual air accidents in this blog from time to time, before last Saturday I had never come across a book that takes a thoughtful, coherent look at the whole history of air accidents and the intriguing problems associated with investigating them. A small bookstore had opened a few months ago in what passes for downtown San Marcos, and I had a few minutes to poke around in it. (Small independent bookstores are going the way of the newspaper before the onslaught of the Internet, but that is a discussion for another time.) My attention was attracted by a striking photo of the French Concorde in flames as it left the ground, and after perusing David Owen's clear, unsensational prose inside, I concluded to buy Air Accident Investigation.

Owen, a former engineer turned journalist, has the disciplined rhetorical skills that one finds more often than not in good British writers. While not pretending to write an exhaustive history, he does start with the early days of commercial aviation, with an even-handed treatment of both U. S. and European practice. I was intrigued by a photo of what has to have been one of the largest biplanes ever built, a Handley Page H. P. 42 flown by Imperial Airways in trans-Channel service in the early 1930s. It was about four stories high and had four engines clustered around the fuselage. Owen's point in including it was that although there were plenty of accidents back then, early commerical aviation was operated so conservatively that in ten years of use, the H. P. 42 never lost a passenger to a fatal accident.

All this changed after World War II, when jet aviation and economic growth transformed the flying public from a few privileged individuals into hordes of airborne bus passengers. Higher speeds and long over-water flights raised the cost of in-flight mechanical failure to the point that surviving a commercial airline crash was a dubious proposition at best.

Most of Owen's examples date from the period of about 1953 to 1990, and are organized by the type of accident: mechanical failure, weather-related, pilot error, and finally terrorism. One theme that emerged out of the dozens of individual tales of smooth takeoffs followed by unexpected tragedies is the role of metal fatigue in airline safety, or lack thereof. It was metal fatigue, poorly understood at the time, that caused the terrible series of accidents to the first British jetliner, the de Havilland Comet, in the early 1950s. And right up to the 1990s, fatigue continues to exact a toll on airliners, their designers, and maintenance personnel who fail to exercise the utmost diligence in checking for and combating this all-too-common problem. I came away with the strong impression that a modern airliner is a kind of chessboard showing the long history of how human ingenuity can checkmate aluminum's tendency to crack under repeated stress caused by the thousands of takeoffs, flights, and landings in a plane's useful service lifetime. Owen points out that although there is no fixed "retirement age" for airframes, the problem of so-called geriatric aircraft will only increase as the industry's fleet ages.

Another factor that is familiar to those who have read a number of engineering-ethics cases is the way that serious accidents have of coalescing from a number of relatively independent small mistakes, each of which if taken in isolation doesn't seem that serious. The investigation of a runway accident between two 747s on the island of Tenerife in the Canaries in 1977 revealed a chain of problems beginning with a terrorist bomb that shut down a better-equipped airport nearby, and ended with fortuitous radio interference during the last control-tower message that could have conceivably avoided the accident. As a result, one 747 trying to take off collided with another on the ground, killing over 500 people in all. This emphasizes the importance of keeping track of the "near-miss" kind of error which could have resulted in fatalities, but didn't simply because other factors were not also wrongly aligned at the time. Good engineering practice is to establish a system for reporting such incidents and making sure that even mildly dangerous problems do not arise in the future.

The book is illustrated with helpful original diagrams that clarify the often complex situations involved in many accidents. Owen's engineering background gives him a confident familiarity with the technical aspects of aviation, but he always makes sure that the essential details are clear enough for the reasonably intelligent reader to follow. Add to this the inherent suspense of reading about unexpected death and destruction, and how investigators painstakingly piece together evidence (sometimes quite literally) after a crash, and you have a book that is both a valuable addition to the engineering ethics literature, and a fascinating read as well. Which is, frankly, an unusual combination, although it need not be.

Owen's book is still in print (in fact, it's in its third edition), so I would highly recommend it for anyone interested in the technology of aviation or the drama of accident investigations. Notably, the rate of serious accidents has fallen off in the last decade or two, largely because jet aviation is now a mature technology. Many of the major ways aircraft and air transportation systems can fail are pretty well known by now and avoidable. We can only hope that, in spite of terrorism and war, air travel safety keeps improving to the point that major air disasters will recede into the distant past.

Sources: David Owen's Air Accident Investigation (3rd edition, 2006) is published by Haynes Publishing, Somerset, England (ISBN 9978 1 85260 614 5).

No comments:

Post a Comment