Research Papers

Modeling and Specification of Time-Limited Dispatch Categories for Commercial Aircraft

[+] Author and Article Information
D. R. Prescott, J. D. Andrews

Department of Aeronautical and Automotive Engineering, Loughborough University, Leicestershire LE11 3TU, UK

J. Dyn. Sys., Meas., Control 130(2), 021004 (Feb 29, 2008) (10 pages) doi:10.1115/1.2837308 History: Received May 31, 2006; Revised June 29, 2007; Published February 29, 2008

Time-limited dispatch allows the degraded redundancy dispatch of aircraft. Aircraft can be dispatched with certain control system faults and fault combinations for specified periods of time if the failure rates from those configurations meet certification requirements. The various system faults and fault combinations are assigned to dispatch categories according to these failure rates. This gives the dispatch criteria for the system. The overall failure rate of the system can then be calculated according to the dispatch criteria. Dispatch criteria are allocated to a small example system, and the system is subsequently modeled using a reduced-state Markov approach currently recommended in SAE ARP5107. An alternative method of setting dispatch criteria and modeling systems, using Monte Carlo simulation, is proposed in this paper, and this technique is also applied to the example system. Dispatch criteria applied to the different models are seen to differ, as are the system failure rates calculated using the different models. A method for setting the dispatch criteria for a system using a Monte Carlo simulation approach is introduced. The method is applied to a simple system, giving auditable results that exhibit the expected behavior for such a system. Because restrictive assumptions in the mathematics are unnecessary with Monte Carlo simulation, it is expected to give more accurate results in comparison to Markov approaches. Also, the results of the reduced-state Markov model appear to be largely dependent on failure rates, which are very difficult to determine.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 4

The combination of multiple faults (MEL maintenance)

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Figure 7

Illustration of how to calculate the instantaneous LOTC rate from a dispatchable fault state

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Figure 8

Example system block diagram

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Figure 9

Fault tree of system shown in Fig. 8

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Figure 10

Dual fault state Markov model showing only failure transitions

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Figure 6

Algorithm for finding the system LOTC rate

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Figure 5

A general dual fault state Markov model

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Figure 3

Multiple faults (MEL maintenance)

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Figure 11

Plot of the results obtained for a STD interval of 200h using the dual fault state Markov and simulation (MCS) approaches



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