Incident Overview
While the aircraft was cruising at flight level 390, the autothrottles and autopilot disengaged without warning. The captain's instruments simultaneously failed, and the cockpit lighting cycled repeatedly between on and off states. The left generator light illuminated on the overhead panel, and the Engine Indicator and Crew Alert System (EICAS) ceased to function. A banging noise was heard cycling in the cockpit, accompanied by an acrid odor.
Cockpit Electrical State
The left AC bus and the left transfer bus were deenergized as a result of the electrical anomalies. The captain made the decision to divert to the nearest suitable airport.
Investigation Results
A subsequent engineering investigation revealed multiple component failures. Specifically, a shorted diode was identified in the left Generator Control Unit (GCU). The Integrated Drive Generator (IDG) was found to be defective. Additionally, a short circuit existed in the input power filter of the EICAS system. The Bus Tie Bar (BTB) was also determined to be defective.