From SKYbrary Wiki
A Ground Collision (GCOL) is defined as a collision that occurs while an aircraft is taxiing to or from a runway in use (ICAO). The definition includes collisions with an aircraft, person, ground vehicle, obstacle, building, structure, etc., but excludes ground collisions resulting from events categorized under Runway Excursion (RI), Wildlife Strike, or Ground Handling (RAMP). RAMP events are defined as occurrences during, or as a result of, ground handling operations.
ICAO references GCOL an Occurrence Category, which are categories used to classify occurrences (i.e. accidents and incidents) at a high level to permit analysis of the data in support of safety solutions. It is important to note that ICAO categorizes pushback/powerback/towing events as RAMP events. Collisions that occur while an aircraft is moving under its own power in the gate, ramp or tiedown area (other than powerbacks) are coded as GCOL.
The GCOL occurrence category is one of several categories – the others being abnormal runway contact (ARC), Bird Strike (BIRD), Runway Excursion (RE), Runway Incursion (RI), loss of control on the ground (LOC-G), collisions with obstacles (CTOL), and undershoot/overshoot (USOS) – that ICAO classifies as runway safety-related. Runway safety events have been identified by ICAO as one of three high-risk accident categories. The other high-risk categories are Loss of Control-Inflight (LOC-I) and Controlled Flight into Terrain (CFIT).
EUROCONTROL’s Safety Improvement Sub-Group (SISG), in its “Operational Safety Study: Controller Detection of Potential Runway and Manoeuvring Area Conflicts,” defines ground collision as a distinct safety event in which an aircraft impacts (or is struck by) another aircraft, vehicle or object in the aerodrome’s manoeuvring area.
The SISG analysed 20 ground safety events comprising both RIs and ground collisions. Some events were accidents, some were incidents, and some yielded “lessons learned” relevant to mitigating the risks of both RIs and GCOLs. Below are are some examples of the areas and risk issues reviewed.
GCOL-relevant research about departing/landing on a taxiway (not a runway) explored these risk issues:
- Landing/departing on a taxiway after a non-conformance with ATC clearance due to spatial/positional confusion; and,
- Landing/departing on a taxiway after non-conformance with ATC clearance due to a misinterpretation [of clearance] or [misheard] clearance.”
GCOL–relevant research about incorrect aircraft movement on the aerodrome manoeuvring area explored these risk issues (any issues involving pushback/powerback would be considered RAMP):
- Aircraft takes taxi route with potential conflict after an incorrect ATC clearance;
- Aircraft enters on to manoeuvring area with potential conflict after an incorrect ATC clearance;
- Aircraft takes incorrect taxi route after a non-conformance with ATC clearance due to spatial/positional confusion;
- Aircraft incorrectly enters onto manoeuvring area after a non-conformance with ATC clearance due to spatial/positional confusion;
- Aircraft takes incorrect taxi route after non-conformance with ATC clearance due to a misinterpretation [of clearance] or [misheard] clearance
- Aircraft incorrectly enters onto manoeuvring area after non-conformance with ATC clearance due to a misinterpretation [of clearance] or [misheard] clearance;
- Aircraft takes incorrect taxi route due to poor [crew resource management (CRM)] or [forgotten] planned action; and,
- Aircraft incorrectly enters onto manoeuvring area runways without ATC clearance due to poor CRM or [forgotten] planned action.
The following are factors that may contribute to GCOL events:
- Failure of stakeholders to proactively ensure that aircraft are not involved in collisions with other aircraft when moving on the manoeuvring area, and that the jet engine exhaust gases from large aircraft do not create a threat for small aircraft;
- Failure to ensure safe parking and docking of aircraft;
- Failure to proactively mitigate the risk of impact damage to parked aircraft or to ensuring that a maintenance inspection — even for apparently minor impact — is conducted prior to any further flight operations;
- Failure to provide adequate signage, markings and lighting that enable aircraft flight crews to comply with taxy clearances; and,
- Failure to train — at a level of quality consistent with aviation professionals — the various types of unlicensed contractors and subcontractors who conduct and supervise aircraft ground-handling tasks on the manoeuvring area and/or in the vicinity of an aircraft parking stand or gate.
Defences and Solutions
The following ATC safety barriers — when deployed and employed correctly — are effective in “alerting ATC to a runway incursion or a ground safety event in sufficient time for ATC to act in order to prevent a ground collision" (SISG):
- Direct visual detection of conflict on the manoeuvring area,
- Indirect detection using remote camera displays,
- Detection following a pilot/vehicle driver report,
- Detection using basic surface-movement radar,
- Detection using an advanced surface movement guidance and control system (A-SMGCS Level 1) or based on an alert from A-SMGCS Level 2; and,
- Detection after an alert from an integrated tower working position (ITWP) or from aerodrome infrastructure that detects aircraft entry onto the runway (e.g., magnetic loops or lasers);
The SISG credited three safety barriers as those most often stopping a developing ground collision: conflict resolution by an air traffic controller alerted by a pilot or vehicle driver (especially when vehicles display high-visibility flashing/strobing lights in all visibility conditions), the controller’s own “belated (last-minute)” visual detection of a conflict, and the pilot’s “belated (last-minute)” visual detection of a conflict. Effective risk mitigation during taxi operations depends on aircraft commanders exercising their full responsibility for safety during this phase of flight.
Assuming that ATC maintains situational awareness and issues a correct taxi clearance — and the aircraft flight crew complies with clearances or standard routings — the highest risk of wing tip collision occurs when multiple aircraft are holding or taxiing in the manoeuvring area (e.g., near a runway entry point, changing the queuing order (especially at night) or moving without benefit of visible taxiway centrelines; Flight crews of swept-wing aircraft must stay alert to the physical clearance during a turn in which 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.
Air traffic controllers should be attentive and proactive in providing progressive taxi instructions if flight crews seem unfamiliar with the aerodrome manoeuvring area or have difficulty because of a particularly unintuitive procedure or a temporarily complex layout (e.g., taxiways closed due to construction work or recently changed taxiway diagram or signage).
Accidents & Incidents
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, that 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.
A343 / RJ1H, Copenhagen Denmark, 2016 — On 26 December 2016, the wing of an Airbus A340-300 being repositioned out of service by towing at Copenhagen as cleared hit an Avro RJ100 which had stopped short of its stand when taxiing due to the absence of the expected ground crew. The RJ100 had been there for twelve minutes at the time of the collision. The Investigation attributed the collision to differing expectations of the tug driver, the Apron controller and the RJ100 flight crew within an overall context of complacency on the part of the tug driver whilst carrying out what would have been regarded as a routine, non-stressful task.
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.
A124, Zaragoza Spain, 2010 — On 20 April 2010, the left wing of an Antonov Design Bureau An124-100 which was taxiing in to park after a night landing at Zaragoza under marshalling guidance was in collision with two successive lighting towers on the apron. Both towers and the left wingtip of the aircraft were damaged. The subsequent investigation attributed the collision to allocation of an unsuitable stand and lack of appropriate guidance markings.
A320, Lisbon Portugal, 2015 — On 19 May 2015, an Airbus A319 crew attempted to taxi into a nose-in parking position at Lisbon despite the fact that the APIS, although switched on, was clearly malfunctioning whilst not displaying an unequivocal ‘STOP’. The aircraft continued 6 metres past the applicable apron ground marking by which time it had hit the airbridge. The marshaller in attendance to oversee the arrival did not signal the aircraft or manually select the APIS ‘STOP’ instruction. The APIS had failed to detect the dark-liveried aircraft and the non-display of a steady ‘STOP’ indication was independently attributed to a pre-existing system fault.
- "Ground Operations" by SKYbrary, 22 September 2017.
- "Occurrence Category Taxonomy" by SKYbrary, 20 June 2012
- “Operational Safety Study: Controller Detection of Potential Runway and Manoeuvring Area Conflicts” Edition 1.0, by EUROCONTROL Safety Improvement Sub-Group, 1 December 2015.
- “Wing Tip Clearance Hazard” by SKYbrary, 4 August 2017.
- "Runway Safety Program - Global Runway Safety Action Plan," by International Civil Aviation Organization (ICAO), First Edition, November 2017
- “Advanced Surface Movement Guidance and Control System (A-SMGCS)” by EUROCONTROL, 9 October 2018.
- “Surface Movement Radar” by SKYbrary, 4 August 2017.
- “Controller Detection of Manoeuvring Area Conflicts” by EUROCONTROL, 27 October 2017.
- “Controller Detection of Manoeuvring Area Conflicts – Safety Barriers” by SKYbrary, 18 May 2016.
- “Controller Detection of Manoeuvring Area Conflicts – Guidance for Controllers” by SKYbrary, 27 June 2016.
- Ground Accident Prevention (GAP) Program by Flight Safety Foundation, 2003.
- Airside Safety Handbook by Airports Council International, 4th edition, 2010.
- Aircraft Ground Handling and Human Factors: A Comparative Study of the Perceptions by Ramp Staff and Management by NLR Air Transport Safety Institute, NLR-CR-2010-125, 2010.
- Ground Vehicle Operations to Include Taxiing or Towing an Aircraft on Airports, Advisory Circular (AC) 150/5210-20A, U.S. Federal Aviation Administration (FAA), 1 September 2015.
- Operational Safety on Airports During Construction, AC 150/5370-2G, by FAA, 13 December 2017.
- ISAGO Standards Manual, 7th Edition, by International Air Transport Association (IATA), IATA Safety Audit for Ground Operators (ISAGO), February 2018.
- "What’s on Your Runway? — NOTAMs enhanced with airport diagrams help pilots mitigate risks during U.S. runway/taxiway construction." by Wayne Rosenkrans, Flight Safety Foundation AeroSafety World, July 2012.