Incident Overview
During a night pushback operation, an aircraft rolled forward moments after it was disconnected from its tow vehicle. The movement pinned a wing walker against an object, resulting in serious injuries. The pushback was conducted using hand signals for communication between the ground crew and flight crew, rather than the standard headphone intercom system.
Sequence of Events
According to the wing walker, they gave the captain a hand signal to set the parking brake, and the captain returned the same signal. The captain, however, reported that the last hand signal he received was to start the engines. After starting the number one engine, the first officer felt the aircraft begin to move forward. The first officer then asked the captain if the parking brake should be set, at which point the captain looked down and engaged the parking brake. Simultaneously, the tug driver signaled a problem, prompting the crew to shut down the engine.
Checklist Compliance
The aircraft's Before Start Checklist explicitly requires the parking brake to be set before engine start. In this instance, the parking brake was not set at the time of engine start, leading to the unintended forward movement after tow release.
Contributing Factors
The investigation noted that hand signals were used instead of the recommended headphone communication during the night operation. The discrepancy between the wing walker's and captain's recollection of the hand signals—specifically regarding the brake set signal—highlights potential communication challenges in such conditions.