Summary
We propose to adopt a new airworthiness directive (AD) for Agusta S.p.A. Model AB139 and Model AW139 helicopters. This proposed AD would require inspecting the thickness of the tail gearbox (TGB) central housing (housing). This proposed AD is prompted by reports that the housing thickness does not conform to its type design. The actions of this proposed AD are intended to detect and correct an unsafe condition on these products.