A de Havilland Canada DHC-8-311Q (Dash 8) was being readied for a flight from Aberdeen-Dyce Airport on this day on this day in aviation history. With the 50 passengers boarded, the crew of four was completing the final preparations for the flight after all doors were closed.
The GPU resting against the aircraft, note the damaged propellor (© AAIB)
The aircraft systems were powered by a 28V DC (Direct Current) Ground Power Unit while it was parked at Stand 8. After the start-up clearance was received and the necessary checklists were completed both the aircraft's Pratt & Whitney Canada PW123 engines were started. With both engines stabilised the crew signalled to ground staff that they could disconnect the Ground Power Unit (GPU), a Houchin C762. The Houchin C762 is a self-propelled GPU with a diesel engine which was capable of either supplying aircraft with electrical power via a generator or propelling the vehicle.
Shortly after the GPU cables were disconnected from the aircraft the GPU moved forward and struck the rotating propellor of the right engine, damaging the propellor, before coming to a stop against the aircraft fuselage. The engines were quickly shut down by the crew and the passengers disembarked the aircraft via the passenger door. There were no injuries to the aircraft's occupants and ground staff.
The incident aircraft at an unknown date (Source; coralsea.sakura.ne.jp © Unknown)
The Air Accident Investigation Branch (AAIB) was alerted and an investigation was launched. After the incident on-site investigation was completed the aircraft was towed to a hangar where it was inspected. There were three main areas of damage to the aircraft as follows;
The right propeller had suffered significant damage to all four blades and to its hub. (parts of the propellor were found on the driver seat of the GPU)
The right engine had come to an abrupt halt and, as a result, the engine required a complete overhaul.
There was a dent in the fuselage with associated local damage to the fuselage structure.
The GPU was also inspected and was found to be extensively damaged;
Windscreen shattered
The left and right windows in the cab doors shattered
Structural damage to the cabin
A subsequent inspection of the GPU found several technical discrepancies with the GPU which made it possible for it to roll away and strike the propellor. Three factors were identified as contributing to the accident;
Higher engine speed in idle due to worn an disconnected parts this caused the GPU to override the applied parking brake
The gate on the drive selector worn
The GPU was facing the propeller, according to regulations it should have been facing away from their propellor
Several safety recommendations were made as a result of this accident to prevent reoccurrence. The Dash 8 was repaired and returned to service. The full AAIB report, on which this blog is based, is available for the readers' reference, providing detailed information on the accident and the investigation. Click on the .pdf file below to access the report;