National Transportation Safety Board Report 217
the regulations may have been inadequate in that they did not require the manufacturer to account for multiple malfunctions resulting from a single failure, even though that failure was considered to be extremely improbable. McDonnell Douglas considered the structural failure of the pylon and engine to be of the same magnitude as a structural failure of a horizontal stabilizer or a wing. It was an unacceptable occurrence, and therefore, like the wing and horizontal stabilizer, the pylon structure was designed to meet and exceed all the foreseeable loads for the life of the aircraft. Therefore, just as it did not analyze the effect the loss of a wing or horizontal stabilizer would have on the aircraft's systems, McDonnell Douglas did not perform an analysis based on the loss of the pylon and engine.
@gic supports the decision not to analyze the loss of the wing and horizontal stabilizer. With the loss of either of these structures, further flight is aerodynamically impossible and the subsequent effect of the loss on the aircraft's systems is academic. However, similar logic fails to support the decision not to analyze the structural failure and loss of the engine and pylon, since the aircraft would be aerodynamically capable of continued flight. The possibility of pylon failure, while remote, was not impossible. Pylons had failed. Therefore, fault analyses should have been conducted to consider the possible trajectories of the failed pylon, the possibilities of damage to aircraft structure, and the effects on the pilot's ability to maintain controlled flight. Since the capability of continued flight was highly probable, the fault analysis might have indicated additional steps or methods which could have been taken to protect those systems essential to continued flight.
Therefore, the Safety Board concludes that the design and interrelationship of the essential systems as they were affected by the structural loss of the pylon contributed to this accident.
Although the Safety Board believes that the design of the pylon structure was less than optimum with regard to maintainability, the evidence is conclusive that many pylons were removed from the wing and reinstalled without imposing damage to the structure. There is no doubt, however, that this maintenance operation requires caution and extreme precision because of the minimal clearances at the pylon-to-wing attachment points and the danger of inadvertent impact of the structure.
McDonnell Douglas was apparently aware of the precision