Investigators have found that undetected release of the parking brake and premature removal of chocks led to an EasyJet Airbus A320's suffering damage as it rolled backwards at London Gatwick.
The crew had already carried out cockpit preparation checks, which included checking that the parking brake was on.
Maintenance personnel subsequently probed a braking system defect, which had occurred on the previous sector, and this required the parking brake to be off.
But there was "no requirement" to put the parking brake back on once the task was completed, says the UK's Air Accidents Investigation Branch, and the crew was left "unaware" that it had been released.
The A320 (G-EZTM) was chocked at the time but, after a tug was attached for pushback, the chocks were removed – in breach of the operator's procedures which required chocks to remain in place until all ground equipment was clear of the aircraft. Forward boarding stairs were still in position at the time.
Investigators state that the tug driver discovered that the tug's radio was not functioning and – without communicating with the aircraft crew – disconnected the tug with a view to using a different, serviceable vehicle.
This released the unchocked aircraft and it rolled backwards, sustaining damage to its forward left-hand exit door as well as its fuselage as it struck the stairs. The crew halted the movement with footbrakes.
None of the 168 occupants was injured during the event, which occurred on 26 March this year. The operator's engineering division subsequently reviewed the maintenance task with a view to making recommendations to Airbus, while the ground-handling company has retrained personnel in chocking procedures.