Propulsion system safety analysis methodology for commercial transport aircraft

Airworthiness certification of commercial transport aircraft requires a safety analysis of the propulsion system to establish that the probability of a failure jeopardising the safety of the aeroplane is acceptably low. The needs and desired features of such a propulsion system safety analysis are discussed, and current techniques and assumptions employed in such analyses are evaluated. It is concluded that current assumptions and techniques are not well suited to predicting behaviour of the propulsion system in service. The propulsion accident history of the high bypass ratio commercial transport fleet is reviewed and an alternate approach to propulsion system safety analysis is developed, based on this accident history. Features of the alternate approach include quantified prediction of propulsion related crew error, engine-level reliability growth modelling to realistically predict engine failure rates, and quantified credit for design features which mitigate the effects of propulsion system failures. The alternate approach is validated by applying it to two existing propulsion systems. It is found to produce forecasts in good agreement with service experience. Use of the alternate approach to propulsion system safety analysis during design and development will enable accurate prediction of the expected propulsion related accident rate and identification of opportunities to reduce the accident rate by incorporating mitigating features into the propulsion system/ aeroplane design.