Incident Details
While the aircraft was waiting for takeoff clearance, the captain reported observing a flash of light and detecting a smell of smoke in the cockpit. The captain then initiated the passenger evacuation checklist, and all passengers evacuated the aircraft without further incident.
Examination Findings
Company maintenance personnel examined the aircraft and determined that the No. 1 generator control unit (GCU), located behind the first officer's seat, had experienced an internal failure. The GCU was removed for further examination.
Component Analysis
Further examination of the GCU revealed that a diode located inside a transformer had shorted. This short circuit caused the transformer to overheat, which in turn produced the smoke observed by the crew.
Similar Occurrences
According to Boeing, there have been 12 similar occurrences involving the same type of component failure.