Summary
The FAA proposes to adopt a new airworthiness directive (AD) for Airbus Helicopters Model EC 155B and EC155B1 helicopters. This proposed AD would require replacing the main gearbox (MGB), or as an alternative, replacing the epicyclic reduction gear module for certain serial numbered planet gear assemblies installed on the MGB. This proposed AD would also require inspecting the MGB magnetic plugs, MGB filter, and oil sump for particles. Depending on the outcome of these inspections, this proposed AD would require further inspections and replacing certain parts. This proposed AD would also prohibit installing certain parts. This proposed AD was prompted by the failure of an MGB second stage planet gear. The actions of this proposed AD are intended to correct an unsafe condition on these helicopters.