As G-OBMD commenced passenger disembarkation at Stand 33 the ground maintenance engineer said that he noticed smoke coming from the point where the ground power lead connects to the aircraft. This was followed by a number of flashes (of flame). He immediately went to alert the aircraft Captain and staff. Cabin Crew No. 1 used her own initiative and ordered an evacuation as she understood that it was a serious fire. In addition to using the forward exit onto the airbridge some passengers exited via the overwing emergency doors and down the chute at the rear passenger door also. The evacuation was completed quickly and without incident.
The ground power lead at Stand 33, which is fixed in a ground power pit, was removed for examination. It was found that one of the two fixing bolts connected through the ground power plug had shorted across 2 phases (A & B phases), apparently as a result of damage caused by a vehicle driving over the plug while it lay on the ramp.
This is not an uncommon occurrence.
The short caused severe arcing in the plug when it was connected to the aircraft and switched on. It was this occurrence that was witnessed by the ground maintenance engineer.