Testability demonstration for a flight control system based on sequential probability ratio test method

The flight control system plays an important role in adjusting the attitude of manned or auto-pilot aircrafts. To reduce the fault diagnosis time and accelerate the maintenance actions, many flight control systems have adopted the design for testability. Testability demonstration for the flight control system is needed to check the indexes of testability such as fault detection rate and fault isolation rate. Currently, the standards and statistical methods for the testability demonstration planning have the problems such as large sample, long test period and it is not optimal for the flight control systems which are of complex structure and high cost. A testability demonstration planning method based on the sequential probability ratio test method is proposed as it can decrease the sample size with almost the same operation characteristic as the classical method. Firstly, the decision factor and rules of the sequential probability ratio test method and truncated decision rules are introduced. Secondly, the establishment of failure mode set based on the failure rate for the sequential probability ratio test method is illustrated. Finally, the demonstration of fault detection rate for a flight control system is implemented with the given method and steps. Software named testability demonstration and evaluation system which can calculate the decision criteria, plot decision chart, select failure mode and make decisions is used to assist the implementation of the test. The result shows that the fault detection rate passes the test with a credible performance and the actual sample size is remarkably decreased while comparing with the classical method.