What happened
On 17 March 2004, an Airbus A320-231, registration G-JOEM, was undergoing passenger boarding at Birmingham Airport. The flight was a scheduled passenger service with 168 passengers and 6 crew members on board. During the embarkation process via an airbridge, cabin crew noticed that the bottom edge of the forward left cabin door was pressing against the floor of the airbridge.
Upon investigation by ground staff, it was discovered that the airbridge''s autolevel alarm had been triggered. This alarm indicates either a malfunction in the autolevel system or that the vertical travel motor had operated continuously for the maximum allowed six seconds. Furthermore, the safety shoe—a component designed to trigger the bridge to descend when contact is made with the aircraft door—was missing from the airbridge floor.
To prevent further damage, the ground agent activated the emergency stop, freezing the airbridge position. Passengers were disembarked to relieve pressure on the door, and the airbridge was eventually moved away. The aircraft sustained damage to its door hinges and the bottom edge of the door.
The investigation
The AAIB investigation established that the safety shoe had been removed by maintenance engineers eight days prior due to damage and had not been replaced. Although the airbridge remained in service, the absence of this component removed the secondary protection intended to prevent excessive vertical loads on the aircraft door.
Investigators found that the autolevel sensor wheel had rotated to its full extent and jammed, indicating that the aircraft had descended relative to the airbridge floor. While the autolevel system was found to be functioning correctly once the wheel was freed, the lack of the safety shoe meant there was no mechanism to prevent the bridge from pressing against the door.
Findings
- The absence of the safety shoe removed the secondary protection layer designed to prevent excessive vertical force on the aircraft door.
- The airbridge had been left in an unattended state while the autolevel system was active.
- The safety shoe had been removed for repairs eight days earlier and was not replaced before the bridge was used for the flight.
- The autolevel sensor wheel had jammed at its maximum downward rotation, indicating a continuous descent of the aircraft relative to the bridge.