What happened
On August 7, 1996, an El Al Boeing 747, registration 4X-AXA, arrived at Helsinki-Vantaa Airport from Israel on a scheduled flight. As the aircraft taxied to gate A4, a ground service agent prepared the passenger boarding bridge by selecting the B747 aircraft type on the control panel.
During the aircraft's arrival, the ground agent maintained a hand on the emergency stop button as a precaution. The aircraft taxied to the stop position, but the passenger door was slightly offset from the ideal alignment. Upon seeing an "ESTP" (emergency stop) signal on the guidance panel, the agent activated the bridge's movement to align with the door. While the bridge's distance sensors functioned correctly and stopped the bridge approximately 5 cm from the fuselage, the movement caused the bridge to strike the aircraft's wing root. The collision resulted in a triangular tear, approximately 50 cm by 28 cm, in the upper skin of the wing's composite structure. There were no injuries resulting from the incident.
The investigation
The investigation examined the functionality of the gate guidance system and the bridge's distance sensors. Testing confirmed that the guidance lights and the sensors operated as intended, stopping the bridge at the correct distance from the fuselage.
The investigation also reviewed the ground agent's training and awareness. While the agent was properly trained in bridge operations, they were unaware of the specific wing clearance for this aircraft type, which was an infrequent visitor to the airport. Furthermore, the investigation looked into the clarity of the signaling system, specifically the use of the "ESTP" text on the guidance panel.
Findings
- The primary cause of the collision was the insufficient clearance between the passenger bridge and the aircraft wing root.
- The ground agent was unaware that the wing of the Boeing 747 would be in close proximity to the bridge structure when the aircraft stopped at the designated position.
- The use of the text "ESTP" on the guidance panel was found to be psychologically confusing and lacked clarity, potentially causing momentary hesitation or confusion during critical maneuvers.
- The investigation noted that the guidance system's "STOP" signal is calibrated to trigger early to ensure aircraft stop at an ideal point, but variations in pilot reaction times and taxi speeds can lead to inconsistent stopping positions.