Importance Analysis of the Aircraft Flap Mechanism Movement Failure

Importance measure is used to describe effect of basic event on top event in fault tree, and the basic events can be ranked using the importance measures in probability risk assessment. By taking uncertainty of the basic event probability into account, a new importance measure is proposed on the traditional one. For complicated engineering systems such as aircraft flap mechanism, the probability of the basic event is usually uncertain due to some uncontrollable factors, and this uncertainty may have significant effect on the importance measure of the basic event. The traditional importance measure employs the assumption of the certain probabilities of the basic events, hence the basic events cannot be properly ranked in the case of the uncertain probability. Contrarily, the new importance measure is on the assumption of the uncertain probability of the basic event. By considering the distribution of the traditional importance measure corresponding to the actual uncertainty of the basic event probability, and using a characteristic value, usually the expectation of the importance measure distribution, to describe the effects, the new importance measure can properly rank the basic events with the uncertainty probability. After the probability density evolution method is employed to solve the new importance measure, the basic event importance is analyzed for the unilateral asymmetric movement failure of the aircraft flap mechanism. The results show that the new importance measure solution based on probability density evolution method is efficient under the acceptable precision. Neglect of the actual uncertainty of the basic event probability may introduce error rank, which is demonstrated by the comparison of the illustrations.