Summary
This document proposes superseding an existing airworthiness directive (AD) for Eurocopter Deutschland GmbH (ECD) Model EC135 P1 and EC135 T1 model helicopters. That AD currently requires adding the AD or a statement to the Rotorcraft Flight Manual (RFM) informing the pilot to reduce power and land as soon as practicable if a thump-like sound followed by unusual vibration occurs during flight. That AD also requires visually inspecting the main rotor drive torque strut assembly (strut) for a crack or a break, recording the inspections in the historical or equivalent record, and re-marking and relocating the strut, as appropriate, and replacing any unairworthy strut with an airworthy strut. Also, that AD establishes life limits for certain struts and revises the life limit for other struts. This action would retain the same requirements but would add the ECD Model EC135 P2 and EC135 T2 helicopters to the applicability and would require replacing certain life-limited struts withtitanium struts. This proposal is prompted by the manufacture of a titanium strut that provides a permanent correction to the unsafe condition that led to limiting the life of other struts that have failed. The actions specified by the proposed AD are intended to prevent failure of a strut and subsequent loss of control of the helicopter.