SUMMARY: This AD requires a nondestructive
inspection (NDI), eddy current or fluorescent penetrant inspection
(FPI), of each main gearbox (MGB) upper housing assembly rib on the
left, right, and forward MGB mounting foot at specified intervals
based on the MGB upper housing assembly hours time-in-service
(TIS). If there is a crack, this AD requires replacing the MGB
upper housing assembly with an airworthy MGB upper housing
This AD is prompted by a report of a crack found on the MGB
upper housing assembly left mounting foot forward rib that cannot
be detected visually.
The FAA is issuing this AD to prevent loss of the MGB and
subsequent loss of control of the helicopter.