What happened
On March 10, 2014, at approximately 16:15 local time, an Embraer 170-100 was parked at stand number 10 at Gdańsk Airport (EPGD). During ground handling operations, a ground power unit (GPU) was being repositioned by a handling agent's employee. While attempting to tow the GPU using a tractor, the operator failed to disconnect the power cable from the aircraft first. Instead, the operator connected the GPU's tow bar to the tractor and began moving the unit, which resulted in the power plug being forcibly pulled from the aircraft's socket.
The investigation
The investigation established that the driver of the tractor, who was fully qualified to operate vehicles on the apron and manage the GPU, did not follow the required ground power unit handling procedures. Specifically, the driver bypassed the protocol requiring the disconnection of the electrical cable prior to towing the unit. Upon inspection of the damage, investigators found that the pins within the aircraft's external power socket had been bent due to the force of the disconnection. Additionally, it was noted that one of the locking mechanisms on the external power socket panel (125AL) was inoperative.
Despite the damage, the aircraft was cleared for flight in accordance with the Minimum Equipment List (MEL) and approved maintenance manual procedures.
Findings
- The primary cause of the incident was the failure to follow the correct sequence of actions when disconnecting the ground power unit.
- The operator attempted to tow the GPU while the power cable was still physically attached to the Embraer 170-100.
- The physical damage to the socket pins was a direct result of the cable being yanked from the aircraft by the moving tractor.