A comparison of modelling approaches for the time-limited dispatch (TLD) of aircraft

The time-limited dispatch (TLD) of aircraft allows operators efficiently to meet certification requirements. In order to show that these requirements are met it is necessary to model the aircraft systems to which TLD is being applied. Currently, variations of fault tree analysis and Markov analysis are commonly used. However, in order to apply either of these methods, a number of assumptions are made to assist in the analysis. Monte Carlo simulation (MCS) is presented here as an alternative method of demonstrating the required level of system reliability. A simple system is analysed using a time-weighted average approach, a reduced fault state Markov approach, and an MCS approach. MCS is seen to offer benefits when modelling the application of TLD to a simple system that could also be seen in the modelling of the application of TLD to real aircraft systems.