Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Eurocopter Model EC 135 helicopters. This proposal would require replacing a certain oil cooler fan splined drive shaft (shaft) with a different airworthy shaft and re-identifying the part numbers on the oil cooler fans. This proposal is prompted by two incidents in which the shaft broke. The actions specified by the proposed AD are intended to prevent failure of the shaft, loss of oil cooling, and a subsequent engine shutdown during flight.