Summary
This document proposes superseding an existing airworthiness directive (AD) for Eurocopter Deutschland GmbH (Eurocopter) Model EC135 P1, P2, T1, and T2 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 an 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, 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 require the same actions as the existing AD except that it proposes to change the visual inspection from a one-time inspection to daily inspections; reduces the life limit for aluminum struts; and eliminates the once-only transfer and remarking of certain struts. This proposal is prompted by an incident in which a pilot felt an in-flight increase in vibration and subsequent discovery of a failed strut. The actions specified by the proposed AD are intended to prevent failure of a strut and subsequent loss of control of the helicopter.