Summary
We propose to adopt a new airworthiness directive (AD) for certain Eurocopter Deutschland GmbH (ECD) Model BO-105A, BO-105C, and BO-105S helicopters. This proposed AD is prompted by initial findings from an accident investigation of an ECD Model BO 105 helicopter which indicated deterioration of the main gearbox (MGB) caused by a contaminated oil supply. The proposed actions are intended to detect oil contamination in the MGB, which if not detected, could result in MGB deterioration, MGB failure, and subsequent loss of control of the helicopter.