What happened
During the shutdown checklist, the captain applied the parking brake; however, the aircraft rolled forward. This movement caused the left engine propeller to make contact with a ground power unit (GPU) that had been correctly prepositioned at the gate.
A readout of the Cockpit Voice Recorder (CVR) indicated that the captain stated the parking brake was set. Following the contact with the GPU, the captain stated that the brake was set, to which the first officer responded, "I just set it," and further noted, "Released it when you..."
Following the accident, a tug and tow bar were attached to the nose landing gear of the aircraft, and the parking brake was applied. Attempts to move the aircraft using this method were unsuccessful.
The investigation
The parking brake assembly was removed for examination. Investigators found no evidence of mechanical failure or malfunction within the assembly. It was noted during the inspection that the second notch from the bottom was worn; however, the maintenance manual specifies that the handle should pull tight beyond three notches. A post-accident inspection of the parking brake also revealed no evidence of failure or malfunction.