What happened
On 16 June 2020, a DHC-8-402, registration G-JECK, was prepared for a ferry flight from Aberdeen International Airport to Germany. The aircraft had been in storage at the airport since March 20 and was positioned on a self-manoeuvring stand with a slight 1° slope.
During the pre-departure phase, ground handling personnel and a representative of the aircraft owner removed the wheel chocks. While the mainwheel chocks were removed by the dispatcher, the nosewheel chocks were also removed during a period of miscommunication. The pilots, who were performing independent external and internal inspections, did not notice that the chocks had been taken away.
Approximately 45 minutes after the chocks were removed, the aircraft began to roll forward across Taxiway D. As the aircraft gained speed, it collided with a parked EMB-145EP, registration G-SAJS. The impact caused damage to the forward fuselage and windscreen of G-JECK and dented the right engine nacelle of G-SAJS. There were no injuries to the crew or ground personnel.
The investigation
The AAIB examined CCTV footage, witness statements, and the aircraft's technical systems. The investigation focused on the sequence of chock removal and the state of the aircraft's braking system. Investigators reviewed the maintenance history, noting that the aircraft had undergone routine checks, including engine runs, four days prior to the event.
Technical analysis of the brake system revealed that while the accumulator was initially charged, the hydraulic pressure in the park brake system had gradually depleted over several days of storage. The investigation also looked into the ground handling procedures and the communication between the dispatcher, the aircraft representative, and the flight crew.
Findings
- A misunderstanding between the ground handler and the aircraft representative led to the inadvertent removal of the nosewheel chocks.
- The pilots' focus on completing extensive checklists and inspections meant they did not notice the absence of the chocks.
- The hydraulic pressure in the park brake system had depleted to 0 psi, rendering the parking brake and nosewheel steering ineffective.
- The aircraft's position on a 1° slope provided enough momentum for the roll once the chocks were gone and the pressure had dropped.