A new perspective on Reason’s Swiss cheese model applied to flight testing

François Meignien, Flight Test Engineer, DGA Essais en vol, France

Abstract

To improve flight safety, the aeronautical industry has quickly adopted the model developed by James Reason in 1990, usually known as the “Swiss cheese” model. This model focused on identifying the errors, active or latent, that can be found in any process where the human operator is involved. From there, James Reason proposed to build defences against the conse- quences of such errors. Yet, this approach focused on mishaps to identify root causes and was therefore mainly reactive instead of being proactive. Possible causes for accidents are most of the time identified after “close calls” are reported, or when less fortunate, after accidents hap- pen. This is even more an issue in the world of flight testing since test operations are rarely repetitive.

Recognizing its benefits and limitations, this paper intends to develop a complementary mod- el to the Swiss cheese model, focusing on two points. First, the identification of positive be- haviours should be encouraged. Instead of only reporting deficiencies, people involved with flight testing should try to recognize actions that deviated from the written procedures but improved safety or avoided possible mishaps. Second, the strength of the various defences put into place should be analysed. The Swiss cheese model is based on increasing the number of barriers, safeguards and other defences to avoid accidents, which happen when the “holes”, present in every barrier, are aligned. But consideration should also be given to the strength of each of these barriers, as well as the stress they are put under.