Four-parameter life prediction method for helicopter transmission system was studied.Four-parameter stress-number of cycles (S-N) curve was presented first

and then

the derivation of helicopter transmission component safe S-N curve from material mean S-N curve and the scheme for the component life prediction were introduced in detail.Multi-load coordinating loading technology in fatigue test and a tail gear box(TGB) casing full-scale fatigue test were introduced at the same time.Finally

according to the full-scale fatigue test result and flight load survey data

applying the four-parameter life prediction method

the TGB casing life prediction was performed

which indicates that four-parameter life prediction method is a reliable and effective method and is worth to be generalized.