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Wing Tip Clearance Hazard
Taxiways are designated for use by all or only some aircraft types. Provided ATC do not make errors in issuing taxi clearance and aircraft flight crew comply with clearances or standard routings, the greatest risk of wing tip collision is present when aircraft are holding or manoeuvring, for example on the approach to the runway entry point. Large Aircraft where the wing tip may not be visible to the pilots, may have to manoeuvre, sometimes at night, to change the queuing order. Such movement often needs to be carried out without taxiway centrelines to follow.
The responsibility for aircraft safety when taxying remains wholly with each aircraft commander. Sometimes, the potential hazard of wingtip collision is known to the airport operators, who may mitigated their liability by ATIS or NOTAM statements such as “wingtip clearance is not assured”.
Examples of the way in which wing tip collision has occurred can be found in the reports on the serious incidents listed under below.
All the aircraft involved in these occurrences were, like most modern transport aircraft, swept wing types which are subject to a phenomenon known as ‘swept wing growth’ or ‘wing creep’. This occurs during a turn when the wing tip describes an arc greater than the normal wingspan due to the geometry of the aircraft and the arrangement of the landing gear. It is one of the reasons for the manufacturer’s cautions usually found in the Flight Crew Training Manuals. Although the effect is less noticeable at moderate curvature of turn, it still serves to erode the perceived wing tip clearance in any turn.
- ^ NATA Safety 1st® eToolkit – Volume I, Issue 3 – October 15, 2004
Accidents and Serious Incidents
- B744, Paris CDG France, 2003 (On 18 January 2003, a Boeing 747-400F being operated by Singapore Airlines Cargo on a scheduled cargo flight from Paris CDG to Dubai taxied for departure in darkness and fog with visibility less than 100 metres in places and the right wing was in collision with a stationary and unoccupied ground de/anti icing vehicle without the awareness of either the flight crew or anybody else at the time. Significant damage occurred to the de icing vehicle and the aircraft was slightly damaged. The vehicle damage was not discovered until almost two hours later and the aircraft involved was not identified until it arrived in Dubai where the damage was observed and the authorities at Paris CDG advised.)
- AT72, Shannon Ireland, 2014 (On 26 February 2014, an ATR 72-202 which had been substituted for the ATR42 which usually operated a series of night cargo flights was being marshalled out of its parking position with a new flight crew on board when the left wing was in collision with the structure of an adjacent hangar. The Investigation found that the aircraft type had not been changed on the applicable flight plan and ATC were consequently unaware that the aircraft had previously been parked in a position only approved for the use by the usual smaller aircraft type.)
- A332/A345, Khartoum Sudan, 2010 (On 30 September 2010, an A330-200 was about to take off from Khartoum at night in accordance with its clearance when signalling from a hand-held flashlight and a radio call from another aircraft led to this not taking place. The other (on-stand) aircraft crew had found that they had been hit by the A330 as it had taxied past en route to the runway. The Investigation found that although there was local awareness that taxiway use and the provision of surface markings at Khartoum did not ensure safe clearance between aircraft, this was not being communicated by NOTAM or ATIS.)
- A343 / B752, London Heathrow UK, 1995 (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.)
- B744 / A321, London Heathrow UK, 2004 (On 23 March 2004, an out of service British Airways Boeing 747-400, under tow passed behind a stationary Airbus A321-200 being operated by Irish Airline Aer Lingus on a departing scheduled passenger service in good daylight visibility and the wing tip of the 747 impacted and seriously damaged the rudder of the A321. The aircraft under tow was cleared for the towing movement and the A321 was holding position in accordance with clearance. The towing team were not aware of the collision and initially, there was some doubt in the A321 flight deck about the cause of a ‘shudder’ felt when the impact occurred but the cabin crew of the A321 had felt the impact shudder and upon noticing the nose of the 747 appearing concluded that it had struck their aircraft. Then the First Officer saw the damaged wing tip of the 747 and informed ATC about the possible impact. Later another aircraft, positioned behind the A321, confirmed the rudder damage. At the time of the collision, the two aircraft involved were on different ATC frequencies.)
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