Dan Applegate

F. D. "Dan" Applegate was Director of Product Engineering for Convair, a McDonnell Douglas subcontractor during the early 1970s. He rose from relative obscurity to become the subject of a classic case in engineering ethics when he penned what became known as the "Applegate Memorandum".

On June 12, 1972, American Airlines Flight 96, a McDonnell Douglas DC-10, lost its cargo door while flying over Windsor, Ontario. The pilots lost much of their control, but were able to land the aircraft safely using differential throttling to control glide angle. In the ensuing investigation, it was learned that the door had improperly latched due to a minor electrical problem, and a locking mechanism that was supposed to ensure that the latches were in place could be forced closed even if they were not.

The "Applegate memorandum" was written shortly after the Flight 96 incident, on 27 June, and delivered to Applegate's immediate supervisor J.B. Hurt. Applegate voiced his concerns to management about potential design faults in the door. In his view, these faults could cause the aircraft’s cargo doors to open mid-flight. Should this occur, there would be an instantaneous loss of pressurization of the cargo area. It followed that the pressurised passenger cabin floor, which lay just above, would buckle under the pressure differential. Applegate noted that this precise failure had occurred during ground testing in 1970. He believed that if this were to happen in flight, the plane’s essential control lines (which ran through the floor) would be cut and the pilots would lose control of the aircraft. A potentially fatal crash would seem imminent.

The report included the following:

"The fundamental safety of the cargo door latching system has been progressively degraded since the program began in 1968... The airplane demonstrated an inherent susceptibility to catastrophic failure when exposed to explosive decompression of the cargo compartment in 1970 ground tests".

"Since Murphy's Law being what it is, cargo doors will come open sometime during the twenty-plus years of use ahead for the DC-10... I would expect this to usually result in the loss of the aircraft".

Management believed that his proposed changes would be costly to implement, and there was some debate about who would end up paying for them, Convair or McDonnell Douglas. Applegate's suggestions to upgrade the door, and especially the cabin floor, would have required the aircraft to be grounded, an expensive proposition. Instead, a set of minor changes were made, intended to ensure that the latches were properly seated and the locking handle could not be operated if they weren't. These changes were limited to strengthening some of the locking system's parts, and adding a small window to allow handlers to visually inspect the latches.

Applegate never 'blew the whistle', and in 1974 Turkish Airlines Flight 981 crashed on the outskirts of Paris killing all 346 people onboard. It was later ascertained that the crash was due to the same technical fault Applegate had foreseen two years prior. The changes after Flight 96 had not been made to this aircraft, in spite of the service logs indicating that they had. Introduced as part of a series of lawsuits following the Flight 981 crash, the Applegate memorandum was an important piece of evidence in what turned out to be one of the largest civil lawsuits in history.

See also

• Lists of accidents and incidents on commercial airliners
• American Airlines Flight 96
• Turkish Airlines Flight 981

References

• John Fielder, Douglas Birsch, "The DC-10 Case", SUNY Press, 1992, ISBN 0791410870

This reference is a collection of papers on the DC-10, including a number of studies of the Applegate memorandum

Further reading

• Paul Eddy et al., "Destination Disaster", Quadrangle - The NYT Book Company, 1976, ISBN 0812906195
• Moira Johnston, "The Last Nine Minutes, The Story of Flight 981", Avon Publishers, 1976, ISBN 068803084X

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