Airworthiness Directives: Sikorsky Aircraft Model S-58 and S-58T Series Helicopters

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This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Sikorsky Aircraft Model S-58 and S-58T series helicopters. This proposal would require the removal and replacement of the transmission main gear box ring gear (ring gear) within certain time intervals and would establish a retirement life for the ring gear. This proposal is prompted by reports of failures of the ring gear due to slow-growth fatigue cracks. The actions specified by the proposed AD are intended to prevent failure of the ring gear, failure of the main transmission, and subsequent loss of control of the helicopter.