Design Safety Analysis of Helicopter Rotor and Transmission Systems

Design safety analysis (DSA) is an element of the certification process having the objective of determining whether the design can satisfy the required safety objectives. Analysis methods traditionally applied to aeroplane control systems include numerical procedures that are based upon the standard rules of probability theory. In this paper it is shown from a detailed examination of accident data that helicopter rotor and transmission systems do not confirm to this theory in respect of catastrophic failures. Practical solutions are offered for this problem, and for that posed by the lack of meaningful component failure data. Details are also given of procedures tailored to produce effective analysis of such systems, and for the structuring of failure modes, effects, and criticality analysis (FMECA) to improve their space efficiency by several orders of magnitude.