Action
Final rule.
Summary
We are adopting a new airworthiness directive (AD) for Agusta S.p.A. (Agusta) Model AB139 and AW139 helicopters with a certain generator control unit (GCU), to require replacing each affected GCU with an airworthy GCU. This AD was prompted by laboratory tests which revealed a potential fault in the overvoltage protection on a certain part-numbered GCU. The actions are intended to prevent failure of the overvoltage protection of the GCU, degraded performance of the electrical power generation and distribution systems, a fire, and subsequent loss of control of the helicopter.