Summary
We propose to adopt a new airworthiness directive (AD) for Sikorsky Model S-76A, S-76B, and S-76C helicopters with a main gearbox (MGB) installed that has undergone certain repairs. This proposed AD would require inspecting the MGB lower housing jet bores for leaks, paint or caulk blistering, and liner protrusion. This proposed AD is prompted by several reports of MGB low oil pressure warnings which were determined to be the result of unsecured jet bore liners that had protruded. The proposed actions are intended to prevent failure of the MGB from loss of oil, which could result in subsequent loss of control of the helicopter.