What happened
Shortly after takeoff, the flight crew heard a loud noise described as a "clunk." Immediately following this sound, the right generator fell off line. The crew attempted to reset the right generator, but the effort was unsuccessful. Subsequently, the left generator also fell off line. After a second unsuccessful attempt to reset the left generator, the crew selected emergency power and initiated a return to the airport. The aircraft completed an uneventful landing.
The investigation
Post-incident examination of the electrical system determined that the AC cross tie relay had failed in the closed position. This specific failure prevented the crew from being able to put either generator back on line. Investigators examined both generators and their associated components, but found no evidence of any other malfunctions or failures.