On 15 October 2007, an Airbus 340-300 being operated on a scheduled passenger flight by Air Lanka with a heavy crew in the flight deck was taxiing towards the departure runway at London Heathrow at night in normal visibility when the right wing tip hit and sheared off the left hand winglet of a stationary British Airways Boeing 747-400 which was in a queue on an adjacent taxiway. The Airbus 340 sustained only minor damage to the right winglet and navigation light. The diagram below shows the conflict (but incorrectly shows the A340 as a -600).
Incident A343 / B744, London Heathrow UK, 2007
An Investigation was carried out by the UK AAIB. This noted that the Boeing 747-400 had stopped well clear of a stationary Boeing 777 ahead to preclude the risk of damaging jet blast and to avoid stopping in the turn ahead, this preventing stress on the landing gear and avoiding the use of excessive thrust when taxiing was resumed. The A340 had been cleared along the taxiway past the Boeing 747 and had assumed that the illuminated green centerline lights indicated that a clear route was available.
It was noted that the standard good visibility Automatic Terminal Information Service (ATIS) message was being transmitted to remind all pilots that they remained responsible for wing tip clearance notwithstanding the use of selectable reds and greens during the hours of darkness. The introduction of this caution followed a 1995 collision at this airport in which the wingtip of a taxiing A340 struck the tail of a B757 that was stationary at a holding point: AAIB Bulletin: 7/96 EW/C95/11/4.
It was noted that the taxiway system was safe by design only for the case of one aircraft per block and that since the rear of the stationary B747 extended over a stopbar beneath the aircraft, at the point where the collision occurred, both aircraft were occupying the same taxiway block. ATC were not aware of this fact as they had no means of accurately determining the position of the Boeing 747.
The taxiway lighting system also operated on a block system, so that only one route guiding taxiing aircraft was illuminated in a block at any one time. This meant that the green taxiway centreline lighting along Link 22 to Holding Point A2 was switched on and the green taxiway centreline lights along Link 23, to the rear of the stopbar under the tail of the B747, were extinguished.
The Investigation accepted the challenge faced by flight crews of large aircraft in assessing wingtip clearances as well as in their understanding of ATC instructions and the taxiway design. A number of incidents of a similar nature were noted to have previously occurred at London Heathrow. In all cases, collisions were the result of a wide body aircraft attempting to pass a stationary aircraft waiting at a holding position. These reports identified various factors, including the difficulty in assessing wingtip clearance from the flight deck of large aircraft and the belief of some of the pilots involved that, by maintaining the taxiway centerline, separation between their aircraft and others would be assured. It was also noted that some of the crews involved did not realise that their aircraft had been involved in a collision thus raising the possibility that a ground collision could occur which is not identified in time to prevent one or both aircraft attempting to become airborne, having sustained damage that may affect their airworthiness.
This and previous investigations also disclosed a lack of understanding amongst some pilots of the extent and particularly the limitations of the protection afforded by airfield markings to taxiing aircraft.
The full Report of the UK AAIB Investigation was published on 8 April 2010 and may be seen at the SKYbrary bookshelf: AAIB Bulletin: 4/2010 EW/C2007/10/01 It included one Safety Recommendation:
“It is recommended that Heathrow Airport Limited improve the effectiveness of the warnings issued to pilots of manoeuvring aircraft, to clarify that clearance from other aircraft is not assured in all circumstances, regardless of the ATC taxi clearance.”