Primary finding
Probable cause
Failure of the left generator control unit (gcu), integrated drive generator (idg), right (side) engine indicator and crew alert system (eicas), and bus tie bar (btb).
Investigator assessment
Analysis narrative
While cruising at fl390, the autothrottles and autopilot disengaged, the captain's instruments failed, and the cockpit lighting cycled on and off. The left generator light illuminated, the eicas failed, a cyclic banging was heard, and an acrid odor was noticeable. The left ac bus and transfer bus were deenergized and the captain elected to divert to the nearest suitable airport. Post incident investigation disclosed a shorted diode is the left gcu (generator control unit), a defective idg (integrated drive generator), a short in the input power filter in the eicas (engine indicator and crew alert system), and a defective btb (bus tie bar).
Source record
Factual narrative
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