Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for Turbomeca S.A. Arrius 2F turboshaft engines that have not incorporated Turbomeca Modification Tf75. That AD currently requires replacing the O-ring on the check valve piston in the lubrication unit at repetitive intervals. This proposed AD would require the same repetitive replacements and would require incorporating Modification Tf75 as terminating action to the repetitive O-ring replacements. Modification Tf75 replaces the check valve piston with a piston design not requiring an O-ring. This proposed AD results from the European Aviation Safety Agency (EASA) and Turbomeca S.A. mandating the incorporation of Modification Tf75. We are proposing this AD to prevent an uncommanded in-flight shutdown of the engine, which could result in a forced autorotation landing and damage to the helicopter.