The FAA is proposing to adopt a new airworthiness directive for all Eurocopter BK117C2 helicopters with certain generator control units (GCU) installed. The AD is prompted by reports of internal short circuits in certain GCUs. The proposed actions are intended to replace any affected GCUs to prevent a short circuit, which could result in a loss of electrical generating power, loss of systems required for continued safe flight and landing, and subsequent loss of control of the helicopter.