AD FAA-2010-1107

We are adopting a new airworthiness directive (AD) for the products listed above. This AD requires an inspection to determine the serial numbers of the auxiliary power unit (APU) generator and the left and right engine direct current (DC) generators, and corrective actions if necessary. This AD also requires revising the airplane flight manual. This AD was prompted by a report of a DC generator overvoltage event which caused smoke in the cockpit and damage to numerous avionics and electrical components. We are issuing this AD to detect and correct an overvoltage condition on the DC electrical busses caused by exciter stator winding failures, and subsequent failure of the generator control unit (GCU) overvoltage protection circuitry, which could result in damage to critical electrical and avionics components.