Summary
This document proposes adopting a new airworthiness directive (AD) for the Sikorsky Model S-92A helicopters. The AD would require replacing the main gearbox (MGB) filter bowl assembly with a two-piece MGB filter bowl assembly and replacing the existing mounting studs. The AD would also require inspecting the MGB lube system filters, the housing, the housing threads, and the lockring counterbore and repairing or replacing them as necessary. This proposed AD is prompted by tests indicating that an existing MGB filter bowl assembly can fail under certain loading conditions including those associated with a damaged MGB filter or mounting stud resulting from high frequency maintenance tasks. Testing of the improved MGB filter bowl assembly demonstrates a significant increase in strength and durability over the existing filter bowl. The actions specified by this proposed AD are intended to prevent failure of the MGB filter bowl assembly due to failure of the mounting studs or the filter bowl, loss of oil from the MGB, failure of the MGB, and subsequent loss of control of the helicopter.