Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for Turbomeca Arrius 2 F turboshaft engines. That AD currently requires removing from service certain serial number (SN) fuel control units (FCUs) or replacing the constant delta pressure diaphragm in those FCUs. This proposed AD would require replacing all FCUs not incorporating modification Tf 55 with FCUs that incorporate modification Tf 55. This proposed AD results from the European Aviation Safety Agency (EASA) and Turbomeca expanding the applicability to the full population of FCUs installed on Arrius 2 F turboshaft engines. FCUs not incorporating modification Tf 55 are susceptible to having an improperly assembled constant delta pressure (delta P) diaphragm. We are proposing this AD to prevent an uncommanded engine in-flight shutdown on a single-engine helicopter, resulting in a forced autorotation landing or an accident.