A Critical Review of Probabilistic Safety Criteria for Commercial-Airplane-System Designs

This paper summarizes and examines the United States government's current probabilistic criteria intended to ensure that the systems on commercial airplanes are designed to be acceptably safe. The author divides those criteria into The Primary Regulation, The Secondary Regulation, and The Guidance, explains several specialized terms, and interprets the criteria as a whole in an attempt to make them more understandable. Then he critically examines the criteria, explains why he contends that they are both ambiguous and flawed, and demonstrates how those ambiguities and flaws can cause both airplane systems and flight-crew procedures and training to be grossly underdesigned for safety. Finally he illustrates with an example how the flaws in the criteria can contribute to accidents that involve relatively large flight-crew-failure probabilities as was obviously the case in two recent 737 MAX airplane catastrophic accidents, and suggests how the criteria might be improved to prevent similar accidents in the future.