Reverse engineering gone wrong: A case study

In the engine of a four passenger, private aircraft, the amount of air and fuel supplied to the engine is controlled by a carburetor butterfly valve. This valve consists of a round, thin steel disk attached to a steel shaft which in turn is mounted in steel bushings near each end of the shaft. The pilot adjusts the positioning of the butterfly valve by means of a throttle control. At the time of the 2000 h overhaul the shaft and bushings are inspected, and if overly worn they are replaced. In the present case, it was found that the shaft and bushings were in need of replacement. However, the original manufacturer of the butterfly valve had gone out of business, and a second manufacturer supplied the replacement parts. The second manufacturer used a process known as reverse engineering in manufacturing the parts. That is, he attempted to copy in detail the characteristics of the original shaft and bushings. However, the importance of proper heat treatment was overlooked, and a result the butterfly valve malfunctioned in flight and the plane crashed. The cause of the malfunction is described in greater detail in the paper.