Fly3est
If you refer to the tragic Chinook (234) accident in 86, there were no HUMS installed at the time. It was not "invented" yet. There were discussions as to if oil analysis did show a development or not. HUMS were first introduced in the north sea in 87 and 88. The HUMS was then installed on the Norwegian Chinooks for the duration of the operation until 95, and several cases proved it worked. XMSN's were pulled on HUMS indications alone (single gear tooth issue), cross shaft coupling bolts with missing heads detected twice and flights cancelled, also SOAP analysis trending with samples every 25 proved important and resulted in cancelled flight (impending gen drive shaft brg failure) HUMS is a great additional surveillance tool, but it does require continuous expert judgement and experience databases for comparisons. It is not and i believe it will never become a simple go - nogo box.