Description

On 23 November 1995, in normal daylight visibility, an Airbus A340-300 being operated by Gulf Air on a scheduled international passenger flight from London Heathrow taxied past a Boeing 757-200 being operated by British Airways on a scheduled domestic passenger flight and also departing from London Heathrow which had stopped on a diverging taxiway within the departure holding area for Runway 27R such that the wing tip of the Airbus impacted the tail fin of other aircraft. Two of the 378 occupants of the two aircraft suffered minor injuries and both aircraft were damaged. Passengers were deplaned uneventfully from both aircraft.

Investigation

An Investigation was carried out by the UK AAIB. It was noted that both aircraft were being operated in accordance with their respective ATC clearances. It was established that the prior to the accident during the autumn of 1995, a new access to Block 18 of Runway 27R had been constructed which involved subdividing the previous holding area (Block 92) into three new blocks and the relocation of the compass base formerly in Block 92 to another part of the airport. At the time of the accident, each block of the new layout was found to have had a yellow painted taxiway centreline with green centerline lights at regular intervals. At the end of each block there were stop lines with red lights across the centerlines to mark the extremity of the block. The situation before and after the change is shown below in the diagrams taken from the Official Report:

The collision occurred as the A340 followed an MCDONNELL DOUGLAS MD-11 ahead through Block 137 towards eventual runway entry for a full length departure from Block 19. As it did so maintaining the taxiway centreline, it passed behind the B757, which was waiting for an intersection departure from Block 18 but had stopped 23.6metres prior to the designated Cat 1 Holding Point, noted by the Investigation to be positioned 105 metres from the edge of the Runway.

The diagram of relative position and track below is taken from the Official Report:

The B757 flight crew were aware that they had not positioned their aircraft as near the holding point as they could have done and advised the Investigation that this was intentional, as a precaution against any hazard from full length departing aircraft which might suffer directional control problems, noting that the holding point constituted a target not a limit. The Investigation noted that there did not appear to be “any UK documentation requiring or encouraging pilots to pull forward to the limit of a holding position.”

Most damage from the collision was to the B757 which “was sustained on the lower part of the rudder, with further damage to beams and composite fairing panels aft of the fin's rear spar”. The rudder was split into two and was subsequently replaced, along with a number of rudder attachment bearings. On the A340 damage was largely limited to the left hand winglet, plus minor scratching and denting of the No. 6 slat on the leading edge.

The new taxiway was withdrawn from use immediately after the accident and the Airport Operator subsequently formulated and introduced, with the approval of the Regulatory Authority, revised procedures aimed at containing the risk of collision. These included:

• Provision of new information signs at the entrances to each of the four departure holding areas.
• Issue of a Class II NOTAM showing the four departure hold areas and explaining their significance in terms of the permanently illuminated (in normal daylight visibility) green centerline lighting and reminding pilots that separation from other aircraft is their responsibility in these areas.
• Provision on a trial basis of lighting to illuminate aircraft holding in the taxiway of Block 137.
• Publication of Notices in the UK AIP and in NOTAMS encouraging pilots to pull forward to stop bars given as taxi clearance limits.
• New restrictions on the tactical use of the holding areas by ATC.

The Final Report of the Investigation was published on 4 July 1996 and may be seen in full at SKYbrary bookshelf: AAIB Bulletin No: 7/96 Ref: EW/C95/11/4

One Safety Recommendation was made as a result of the Investigation:

“That the CAA should, in liaison with the appropriate ICAO committees, consider what action may be taken in the longer term to ensure that flight crews of large public transport aircraft are better able to achieve a positive clearance between their aircraft and others while manoeuvring on the ground.” (96-43)

Further Reading

• UK CAA CAP 637 Visual Aids Handbook

SKYbrary articles

• Wing Tip Clearance Hazard
• Taxiway Lighting
• Taxiway Surface Markings and Signs
• A343 / B744, London Heathrow UK, 2007