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Taxiway Collisions

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Category: Ground Operations Ground Operations
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Description

An airport is a complex interface between the air and the ground environments, where access must be controlled and separation between aircraft or between aircraft and vehicular traffic must be maintained and optimised. While most occurrences on airport aprons and taxiways do not have consequences in terms of loss of life, they are often associated with aircraft damage, delays to passengers and avoidable financial costs.

This article examines collisions and near collisions whilst aircraft are on the airport manoeuvring areas inclusive of taxiways and ramp areas. The article On-Gate Collisions provides insight into aircraft collisions occurring whilst on, entering or leaving an assigned gate.

Occurrences

As previously stated, to ensure efficient and safe airport ground operations, separation between aircraft or between aircraft and vehicular traffic must be maintained and optimised. On occasion, however, minimum separation, particularly aircraft/vehicle separation is compromised. Whilst all events do not result in collision with an aircraft, the majority of taxiway occurrences involve vehicle operators deviating from a surface movement controller clearance. These "failure to comply" occurrences most usually involve vehicles:

  • using an incorrect taxiway
  • failing to stop at a taxiway holding point
  • failing to stay on the surface movement control radio frequency or ground frequency as appropriate
  • failing to obtain a clearance before entering an area subject to control.

In all cases, these actions have the potential to put the vehicle in conflict with an aircraft which, in turn, could:

  • lead to collision
  • require aggressive braking by the aircraft which could result in personnel injuries. Cabin crew are especially vulnerable as they might be moving within the cabin preforming pre-departure or post-landing duties


Most of the remaining occurrences are related to one of the following:

  • aircraft-aircraft collisions or near collisions - collisions can result from:
    • failure to follow taxiway centreline guidance
    • failure to stop prior to a stopbar
    • taxiing at speeds unsuited to the conditions or level of congestion
    • taxiway deviation whilst trying to manoeuvre to "squeeze" past another aircraft. Manoeuvring around an aircraft partially blocking a taxiway (as might be the case if the aircraft was approaching, but not yet at the stop point of, a gate) can lead to collision. If misjudged, this could result in a wingtip striking the tail of the stopped aircraft or it could compromise clearance between obstacles or other aircraft and the wingtip opposite the stopped aircraft
    • taxiway configuration - converging taxiways can potentially lead to reduced or compromised clearance, especially where they cross
  • reduced aircraft clearance with ground equipment or obstacles. Reduced clearance accidents or incidents can occur in various ways. These include:
    • inappropriate use of a restricted taxiway - some taxiways are restricted by wingspan. Use by a larger aircraft could compromise obstacle clearance
    • failure to follow taxi lane guidance - deviation from the lane guidance whilst manoeuvring in proximity to light stands, gates or stationary equipment can result in collision
  • jet blast -inappropriate thrust settings or following too closely can result in aircraft damage due to jet blast. Jet blast can also cause unsecured equipment such as Unit Load Devices (ULD) to move and strike other aircraft, equipment or personnel

Prevention

Most taxiway accidents and incidents are preventable. This prevention is dependant upon appropriate training and testing, compliance with clearances, published procedures and right-of-way rules, maintaining situational awareness and adapting speed of movement to suit the weather and surface conditions. Some specific accident prevention strategies are as follows:

  • Vehicle operators - It is imperative that vehicle operators be properly trained, tested and authorised for ramp and taxiway operations. Driving infractions should be investigated and additional training provided where appropriate. Multiple infractions should be considered grounds for suspension of airside driving privileges. Operators should:
    • ensure daily inspection for their vehicle is complete and that beacon/hazard lights are operating when the vehicle is airside
    • maintain situational awareness
    • operate their vehicle safely and in accordance with all company and airport rules
    • obey all "rules of the road" inclusive of speed limits, stop signs and right-of-way guidance
    • yield to aircraft at all times
    • obtain and read back any ground movement controller clearance prior to entering an area where clearance is required. If clearance is not understood, ASK!
  • Tug operators - Tug operators have the additional responsibility of moving aircraft on and off gates as well as positioning aircraft from one location on the airfield to another. In addition to the aforementioned items for vehicle operators, the tug operator must:
    • know the size of the aircraft in tow inclusive of the wingspan
    • be conversant with the normal taxi routes from one airfield location to another
    • understand the stopping distances required for a tug with an aircraft in tow
    • comply with all clearances, especially runway crossing clearances
    • use wing and tail walkers when manoeuvring in congested areas
  • Controllers - The ground controller is responsible for the safe and efficient movement of aircraft and vehicle traffic on the taxiways and aprons. They should:
    • provide the appropriate clearance for the requested action
    • ensure that the clearance readback is accurate
    • to the extent possible, monitor the movement visually, via transponder or by use of multilateration equipment to ensure clearance compliance
  • Pilots - In general, pilots are responsible for the ground movement of an aircraft from the runway to the gate and from the gate to the runway although they may also reposition aircraft from one point on the airfield to another. In all cases they should:
    • request, readback and comply with an appropriate clearance
    • maintain situational awareness
    • taxi at a speed appropriate to the conditions and traffic situation
    • maintain the centre of the taxi lane
    • be vigilant for taxi lane compromise by another aircraft, vehicle or object
    • not assume that vehicles will yield right-of-way

Accidents and Incidents

The following accidents and incidents involve collision or near collision between two aircraft, an aircraft and a vehicle, or an aircraft and a stationary object.

Aircraft/Aircraft Conflict

  • B190 / B737, Calgary Canada, 2014 (On 29 March 2014, a Beech 1900D being taxied by maintenance personnel at Calgary entered the active runway without clearance in good visibility at night as a Boeing 737-700 was taking off. The 737 passed safely overhead. The Investigation found that the taxiing aircraft had taken a route completely contrary to the accepted clearance and that the engineer on control of the aircraft had not received any relevant training. Although the airport had ASDE in operation, a transponder code was not issued to the taxiing aircraft as required and stop bar crossing detection was not enabled at the time.)
  • MD82 / C441, Lambert-St Louis MI USA, 1994 (On 22 November 1994 a McDonnell Douglas MD 82 flight crew taking off from Lambert- St. Louis at night in excellent visibility suddenly became aware of a stationary Cessna 441 on the runway ahead and was unable to avoid a high speed collision. The collision destroyed the Cessna but allowed the MD82 to be brought to a controlled stop without occupant injury. The Investigation found that the Cessna 441 pilot had mistakenly believed his departure would be from the runway he had recently landed on and had entered that runway without clearance whilst still on GND frequency.)
  • DH8C / P180, Ottawa ON Canada, 2013 (On 1 December 2013, a small aircraft taxing for departure at night was cleared to cross an active runway and did so as a DHC8 was taking off from the same runway. Separation was significant and there was no actual risk of collision. The Investigation found that the GND controller had issued clearance to the taxiing aircraft when he had responsibility for its whole taxi route but had neither updated the aircraft status system nor directly advised of the taxiing aircraft when passing responsibility for part of its cleared route to the TWR controller who therefore remained unaware of it.)
  • DH8D / B737, Winnipeg Canada, 2014 (On 4 August 2014, the crew of a DHC8-400 departing Winnipeg continued beyond the holding point to which they had been cleared to taxi as a B737 was about to land. ATC observed the daylight incursion visually and instructed the approaching aircraft to go around as the DHC8 stopped within the runway protected area but clear of the actual runway. The Investigation found that the surface marking of the holding point which had been crossed was "significantly degraded" and noted the daily airport inspections had failed to identify this.)
  • B738 / B738, Dublin Ireland, 2014 (On 7 October 2014, a locally-based Boeing 737-800 taxiing for departure from runway 34 at Dublin as cleared in normal night visibility collided with another 737-800 stationary in a queue awaiting departure from runway 28. Whilst accepting that pilots have sole responsible for collision avoidance, the Investigation found that relevant restrictions on taxi clearances were being routinely ignored by ATC. It also noted that visual judgement of wingtip clearance beyond 10 metres was problematic and that a subsequent very similar event at Dublin involving two 737-800s of the same Operator was the subject of a separate investigation.)
  • MD82 / MD11, Anchorage AK USA, 2002 (On 17 March 2002, at Ted Stevens Anchorage Airport, a McDonnell Douglas MD82 operated by Alaska Airlines, on a night pushback in snow conditions collided with an inbound taxiing McDonnell Douglas MD-11. The MD82 suffered substantial rudder damage although the impacting MD11 winglet was undamaged.)
  • 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.)
  • B733 / DH8D, Fort McMurray Canada, 2014 (On 4 August 2014, a Boeing 737-300 making a day visual approach at Fort McMurray after receiving an ILS/DME clearance lined up on a recently-constructed parallel taxiway and its crew were only alerted to their error shortly before touchdown by the crew of a DHC8-400 which was taxiing along the same taxiway in the opposite direction. This resulted in a go around being commenced from 46 feet agl. The Investigation noted that both pilots had been looking out during the final stages of the approach and had ignored important SOPs including that for a mandatory go around from an unstable approach.)

Aircraft/Vehicle Conflict

  • Vehicle / B752, Dublin Ireland, 2009 (On 29 May 2009, a Boeing 757-200 being operated by UK Airline Thomson Airways on a passenger charter flight from Sharm-el-Sheikh, Egypt to Dublin and having just landed on runway 10 at destination at night in poor visibility overtook a small ride-on grass mower moving along the right hand side of the runway in approximate line with the aircraft’s right hand wing tip. The driver of the mower was unaware of the arriving aircraft until he heard it on the runway behind him. Prior to the landing, ATC had been informed that all grass-cutting equipment previously working on and around the runway had cleared it.)
  • Vehicle / PA31, Mackay SE Australia, 2008 (On 29 June 2012, a Piper PA31 taking off from runway 05 on a passenger charter flight just missed hitting an inspection vehicle which had entered the take off runway from an intersecting one contrary to ATC clearance. The overflying aircraft was estimated to have cleared the vehicle by approximately 20 feet and the pilot was unaware it had entered the active runway. The driver had been taking a mobile telephone call at the time and attributed the incursion to distraction. The breached clearance had been given and correctly read back approximately two minutes prior to the conflict occurring.)
  • SB20, Stockholm Arlanda, 2001 (On 18 December 2001, a Saab 2000 being operated by Air Botnia on scheduled passenger flight from Stockholm to Oulu was taxiing out at night in normal visibility in accordance with its ATC clearance when a car appeared from the left on a roadway and drove at speed on a collision course with the aircraft. In order to avoid a collision, the aircraft had to brake sharply and the aircraft commander saw the car pass under the nose of the aircraft and judged the vehicle’s closest distance to the aircraft to be four to five metres. The car did not stop, could not subsequently be identified and no report was made by the driver or other witnesses. The diagram below taken from the official report shows the site of the conflict - the aircraft was emerging from Ramp ‘G’ to turn left on taxiway ‘Z’ and the broken line shows the roadway which is crossed just before the left turn is commenced.)
  • ATP, Jersey Channel Islands, 1998 (On 9 May 1998, a British Regional Airlines ATP was being pushed back for departure at Jersey in daylight whilst the engines were being started when an excessive engine power setting applied by the flight crew led to the failure of the towbar connection and then to one of the aircraft's carbon fibre propellers striking the tug. A non standard emergency evacuation followed. All aircraft occupants and ground crew were uninjured.)
  • B738, London Stansted UK, 2008 (On 13 November 2008, a Boeing 737-800 with an unserviceable APU was being operated by Ryanair on a passenger flight at night was in collision with a tug after a cross-bleed engine start procedure was initiated prior to the completion of a complex aircraft pushback in rain. As the power was increased on the No 1 engine in preparation for the No 2 engine start, the resulting increase in thrust was greater than the counter-force provided by the tug and the aircraft started to move forwards. The towbar attachment failed and subsequently the aircraft’s No 1 engine impacted the side of the tug, prior to the aircraft brakes being applied.)
  • A320, Dublin Ireland, 2017 (On 27 September 2017, an Airbus A320 being manoeuvred off the departure gate at Dublin by tug was being pulled forward when the tow bar shear pin broke and the tug driver lost control. The tug then collided with the right engine causing significant damage. The tug driver and assisting ground crew were not injured. The Investigation concluded that although the shear pin failure was not attributable to any particular cause, the relative severity of the outcome was probably increased by the wet surface, a forward slope on the ramp and fact that an engine start was in progress.)
  • B763, Luton UK, 2005 (On 16 February 2005, at Luton Airport, a Boeing B767-300 collided with the tug pulling it forward when the shear pin of the unserviceable tow bar being used to pull the aircraft broke. The aircraft ran onto the tug when the ground crew stopped the tug suddenly. As result of the collision with the tug the aircraft fuselage and landing gear was damaged.)
  • Vehicle / E190 / E121, Jersey Channel Islands, 2010 (On 1 June 2010, an Airport RFFS bird scaring vehicle entered the active runway at Jersey in LVP without clearance and remained there for approximately three minutes until ATC became aware. The subsequent Investigation found that the incursion had fortuitously occurred just after an ERJ 190 had landed and had been terminated just as another aircraft had commenced a go around after failure to acquire the prescribed visual reference required to continue to a landing. The context for the failure of the vehicle driver to follow existing procedures was found to be their inadequacy and appropriate changes were implemented.)

Aircraft/Object Conflict

  • A346, Toulouse France, 2007 (During ground running of engines, the aircraft impacted a concrete wall at a ground speed of 30 kts following unintended movement and the aircraft was wrecked.)
  • B773, Lisbon Portugal, 2016 (On 13 January 2016 ice was found on the upper and lower wing surfaces of a Boeing 777-300ER about to depart in the late morning from Lisbon in CAVOK conditions and 10°C. As Lisbon had no de-ice facilities, it was towed to a location where the sun would melt the ice more quickly but during poorly-planned manoeuvring, one of the wingtips was damaged by contact with an obstruction. The Investigation attributed the ice which led to the problematic re-positioning to the operator’s policy of tankering most of the return fuel on the overnight inbound flight where it had become cold-soaked.)
  • B737, Amsterdam Netherlands, 2003 (n 22 December 2003, a Boeing 737-700 being operated by UK Operator Easyjet on a scheduled passenger flight from Amsterdam to London Gatwick was taxiing for departure at night in normal visibility and took a different route to that instructed by ATC. The alternative route was, unknown to the flight crew, covered with ice and as a consequence, an attempt to maintain directional control during a turn was unsuccessful and the aircraft left wing collided with a lamp-post. The collision seriously damaged the aircraft and the lamp post. One passenger sustained slight injuries because of the impact. The diagram below taken from the official investigation report shows the area where the collision occurred.)
  • B722, Cotonou Benin, 2003 (On 25 December 2003, a Boeing 727-200 being operated by UTA (Guinea) on a scheduled passenger flight from Cotonou to Beirut with a planned stopover at Kufra, Libya, failed to get properly airborne in day VMC from the 2400 metre departure runway and hit a small building 2.45 metres high situated on the extended centreline 118 metres beyond the end of the runway. The right main landing gear broke off and ripped off a part of the trailing edge flaps on the right wing. The airplane then banked slightly to the right and crashed onto the beach where it broke into several pieces and ended up in the sea where the depth of water varied between three and ten metres. Of the estimated 163 occupants, 141 were killed and the remainder seriously injured.)
  • B738, Surat India, 2014 (On 6 November 2014, a Boeing 737-800 taking off at night from Surat hit an object as it was approaching 80 knots and the take-off was immediately rejected. On return to the gate substantial damage was found to the left engine and a runway inspection found one dead buffalo and another live one. The runway was reopened after removal of the carcass but the live buffalo was not removed and was seen again by the runway the following day. The Investigation found a history of inadequate perimeter fencing and inadequate runway inspection practices at the airport.)
  • DH8D, Hubli India, 2015 (On 8 March 2015, directional control of a Bombardier DHC 8-400 which had just completed a normal approach and landing was lost and the aircraft departed the side of the runway following the collapse of both the left main and nose landing gear assemblies. The Investigation found that after being allowed to drift to the side of the runway without corrective action, the previously airworthy aircraft had hit a non-frangible edge light and the left main gear and then the nose landing gear had collapsed with a complete loss of directional control. The aircraft had then exited the side of the runway sustaining further damage.)
  • 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.)
  • B772, Singapore, 2013 (On 19 December 2013, the left engine of a Boeing 777-200 taxiing onto its assigned parking gate after arrival at Singapore ingested an empty cargo container resulting in damage to the engine which was serious enough to require its subsequent removal and replacement. The Investigation found that the aircraft docking guidance system had been in use despite the presence of the ingested container and other obstructions within the clearly marked 'equipment restraint area' of the gate involved. The corresponding ground handling procedures were found to be deficient as were those for ensuring general ramp awareness of a 'live' gate.)

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