Friday, December 17, 2010


In December 2010, a French court decided that Continental Airlines is criminally responsible in the crash of the Concorde, back in summer 2000, which killed 113 people. Namely, a Continental plane, taking off just minutes earlier, left a piece of debris on the runway, which afterwards punctured the tire of Concorde and lead to the crash.

Should we blame Continental for this crash? Briefly, I believe we should, but just a little.

Events have a large number of causes. In case of Concorde crash, those include the design of the airplane (which was vulnerable to the tire bursting at high speed), the related testing and certification process (which was unable to identify that problem), the plane operators (who did not strengthen the plane despite of numerous similar incidents), the airport in Paris (which could not spot the piece of metal on the runway), and the Continental plane, which left the debris. In a sense, all of them are somewhat responsible.

Unfortunately, causality itself is a tricky concept as well. What is needed for an act to be a cause for something? Perhaps I am guilty if my act was necessary and sufficient to lead to an undesirable outcome. If a soccer player kicks the ball, and the goalkeeper blocks it, and the ball bounces to a window -- who is guilty? Both the kick and the blocking were necessary, but not sufficient. The Concorde case is similar: wrongly repaired thrust reverser was necessary but not sufficient for the accident.

To overcome this paradox, we need a more complex concept of responsibility. As the court ruled for 70% of the compensation claims to be paid by Continental, it implicitly stated that the Continental was to be blamed for about 70% of the crash. I believe this is the right way to think about similar cases (although I would go for a smaller percentage here). There are many culprits, but they are of different importance. It was a shared responsibility where Continental had a (minor) part.

Is there a consistent way to establish one's "share of blame"? I doubt it. But we may still try.

First, it is not acceptable that a departing plane drops large pieces of metal on the runway. Second, for years Air France knew the problems with bursting tires and potential damage it caused. However, little was done. This is unacceptable as well. One might propose something along the following lines: First, calculate what is the expected cost for the other airlines (including eventual crashes) if a plane drops a piece of metal, given everyone follows the procedures which was deemed appropriate in summer 2000 (call theses costs A). Next, calculate how often would Concorde crash due to bursting tires, using the procedures and technology as it was used by Air France during the time of the crash, without any debris on the runway (call related costs B). In total, A + B correspond to the sum of costs, both of which are sufficient but not necessary for the accident. Now find, what would be the second likelihood, given there is similar debris on runway (call this C). The difference C - B corresponds to the extra costs for Air France, caused by the debris, but also by the weak design of the Concorde. The Continentals "guilt" might be (A + 1/2 (C - B))/(A + C), i.e. the costs Continental caused alone (A), plus a half of the extra (1/2 (C - B)) as a percentage of the total costs (A + C).

Although the the proposal above has many shortcomings, it helps to analyse situations where there is no single ultimate "guilty" part.