This paper presents a synopsis of an extensive failure mode investigation and analysis of Bell UH-1 and Vertol CH-47 transmissions. Correlation of these observed field experiences with conventional design stress analysis techniques and preliminary bench test data is presented. Lubrication states as defined by elastohydrodynamic film thickness calculations are shown to offer explanation for the existence of many failure modes which are not predicted by conventional analyses. Simple statistical methods for failure data analysis are employed as an aid to assessing relative gain in reliability afforded through correction of dominant failure modes. The premise is advanced that the key to successful design of advanced helicopter power transmissions featuring significant increases in operational reliability may be found in the application of these lessons.