Civil aircraft airworthiness verification method and application of auxiliary power unit inflight start function

Airworthiness requirements for APU in-fight start function in CCAR 25 is analyzed.Based on the guidance in advisory circular, a executable method for compliance verification is proposed and applied on a domestic civil aircraft. Binomial distribution is introduced in start reliability tests to determine total number of test points need do.As a result, for the first time, the APU in-flight cold soak start was carried out on a domestic civil aircraft, and the in-flight cold soak time was as long as 4 hours. And, a minimum of 95% APU in-flight start reliability is verified on a domestic civil aircraft using the method established.