What happened
On the night of 15 October 2007, an Airbus A340-311, registration 4R-ADC, was taxiing at London Heathrow Airport following a pushback from Terminal 4. The crew was proceeding toward Holding Point A2 under night conditions with 8 km visibility. During the taxi, the crew attempted to pass a stationary Boeing 747-436, registration G-BNLL, which was positioned on an adjacent taxiway.
While navigating the intersection of taxiways Link 22 and Link 23, the right wingtip of the 4R-AADC struck the left winglet of the G-BNLL. The impact caused the left winglet of the Boeing 747 to detach, losing approximately 1.7 metres of its tip. The Airbus A340 also sustained damage to its right navigation light assembly and the leading edge of its right winglet. Following the contact, the crew of the 4R-ADC notified Air Traffic Control (ATC) of the potential collision, and the Airport Fire Service was dispatched to inspect both aircraft for fuel leaks. No injuries were reported to the passengers or crew on either aircraft.
The investigation
The investigation examined the cockpit procedures, the interpretation of ATC instructions, and the taxiway lighting and design. It was established that the crew of the 4R-ADC believed that the ATC clearance to follow green centerline lights to Holding Point A2 implied that the path was clear of obstructions. The investigation also reviewed the taxiway lighting system, noting that the lights operated on a block system. As the 4R-ADC moved into a new block, the lights on the preceding section were extinguished, which contributed to the crew's perception of the available space.
Furthermore, the investigation looked into the physical limitations of the flight deck. The commander's position in the left seat made it difficult to accurately assess wingtip clearance, especially as the aircraft drew level with the stationary G-BNLL. The investigation also considered the impact of the airport's recent taxiway re-development and the effectiveness of the ATIS warnings regarding wingtip clearance.
Findings
- The primary cause of the collision was the inaccurate assessment of wingtip clearance by the crew of the 4R-ADC.
- The crew misinterpreted ATC instructions and the illuminated green centerline lights as a guarantee that no obstructions existed on their path.
- The physical configuration of the flight deck and the darkness of the environment hindered the commander's ability to judge the distance between the two large aircraft.
- The acute angles between the aircraft during the passing maneuver created a visual illusion of greater separation than actually existed.
- The taxiway lighting system design, which extinguishes lights behind a moving aircraft, contributed to the crew's lack of awareness regarding the proximity of the stationary G-BNLL.
Safety action
- Safety Recommendation 2010-010: It is recommended that Heathrow Airport Limited improve the effectiveness of warnings issued to pilots to clarify that wingtip clearance is not guaranteed in all circumstances, regardless of ATC taxi clearances.