Basic Flaws in Vaughan's Analysis of the Challenger Accident

Cite as: Lighthall, F. F. 2014, “Basic Flaws in Vaughan's Analysis of the Challenger Accident”.

Diane Vaughan’s (1996) widely cited analysis of the causes of the Challenger accident makes six serious errors. Vaughan’s errors interpreting the technical dynamics that caused the accident rendered inaccurate her analysis of the human failures that caused the fatal physical malfunction.

Vaughan assumed that the best form of explanation of the process that produced the disaster would be a continuous, cumulative cause rather than a discontinuous, suddenly emerging cause precipitating the disaster. Second, she considered design specifications of the shuttle’s components to be the only legitimate criteria of safe shuttle functioning – despite the fact that those specifications were written before the shuttle was built, before its flight complications could be known. Any deviation (“anomalies”) in actual flight performance from those specifications Vaughan viewed as ipso facto dangerous. Therefore, any empirical tests engineers conducted showing as harmless a particular deviation from design that occurred on several occasions -- one form of O-ring erosion (“impingement” erosion) -- constituted a dangerous “normalization of deviance.” The repeated framing of that deviating anomaly as safely corrected -- thus “normalizing” the supposedly dangerous anomaly -- played a crucial role, according to Vaughan, in causing the disaster.

Third, Vaughan mistakenly assumed that it was erosion of O-rings in a booster joint that caused the O-rings to fail to seal the joint. Fourth, Vaughan misread a central table of engineering data, interpreting the effect of cold temperature as making the O-rings harder therefore slower to seal and so subject to a fatal amount of erosion. This dynamic was present, but negligible in relation to the dynamics that actually caused the failure. Vaughan missed the actual, more complicated dynamic of cold temperature and its effect on the sealing shape of the O-ring. Fifth, Vaughan argued that the engineers and managers involved in the launch decision violated no norms; instead they conformed to all norms of decision making and safety. Finally, Vaughan’s analysis failed crucially to include the definitive post-accident evidence and analysis of the physical causes of the accident, results of two independent studies showing that cold O-rings without erosion failed to seal booster joints.

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