Action
Notice of proposed rulemaking (NPRM).
Summary
We propose to adopt a new airworthiness directive (AD) for Agusta S.p.A. (Agusta) Model AB139 and AW139 helicopters with a certain generator control unit (GCU). This proposed AD was prompted by laboratory tests which revealed a potential fault in the overvoltage protection on a certain part-numbered GCU. This proposed AD would require replacing each affected GCU with an airworthy GCU. In addition, any affected GCU is not approved for installation on any helicopter. We are proposing this AD 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.