Ground Collision

Definition

Ground Collision (GCOL) - a collision that occurs while an aircraft is taxiing to or from a runway in use.

Source: ICAO

Note: 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 (RE), Wildlife Strike, or Ground Handling (RAMP). RAMP events are defined as occurrences during, or as a result of, ground handling operations.

Description

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.

Scenarios

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.

Contributory Factors

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):

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

Aircraft–Aircraft

On 3 February 2019, two aircraft which had just landed on adjacent parallel runways almost collided during their taxi in after one failed to give way to the other at an intersection as instructed causing the other to perform an emergency stop which was achieved just in time to avoid a collision. Whilst not attributing direct cause to other than the crew of the aircraft which continued high speed taxiing as the intersection was approached, having noted that all taxiway lighting at Amsterdam is permanently lit at night, a range of factors were identified which had facilitated the error made.

On 13 January 1982, an Air Florida Boeing 737-200 took off in daylight from runway 36 at Washington National in moderate snow but then stalled before hitting a bridge and vehicles and continuing into the river below after just one minute of flight killing most of the occupants and some people on the ground. The accident was attributed entirely to a combination of the actions and inactions of the crew in relation to the prevailing adverse weather conditions and, crucially, to the failure to select engine anti ice on which led to over reading of actual engine thrust.

On 5 February 2011, an Airbus A319-100 being operated by Air Berlin on a passenger flight departing Stockholm inadvertently proceeded beyond the given clearance limit for runway 19R and although it subsequently stopped before runway entry had occurred, it was by then closer to high speed departing traffic than it should have been. There was no abrupt stop and none of the 103 occupants were injured.

On 18 June 2010 a Sun Express Boeing 737-800 taxiing for a full length daylight departure from runway 06 at Prague was in collision with an Airbus 321 which was waiting on a link taxiway leading to an intermediate take off position on the same runway. The aircraft sustained damage to their right winglet and left horizontal stabiliser respectively and both needed subsequent repair before being released to service.

On 14 April 2011, a Ryanair Boeing 737-800 failed to leave sufficient clearance when taxiing behind a stationary Boeing 767-300 at Barcelona and the 737 wingtip was in collision with the horizontal stabiliser of the 767, damaging both. The 767 crew were completely unaware of any impact but the 737 crew realised the close proximity but dismissed a cabin crew report that a passenger had observed a collision. Both aircraft completed their intended flights without incident after which the damage was discovered, that to the 767 requiring that the aircraft be repaired before further flight.

Aircraft–Object/Vehicle

On 8 September 2020, an airport maintenance team driving at night on the centreline of the active runway at Birmingham were unaware that an inadequately secured 2 metre-long ladder had fallen from their pickup truck. Three aircraft then landed in the following half hour narrowly missing the ladder before it was discovered and the runway closed. The Investigation found that a more suitable alternative vehicle was available and that the completely inadequate method used to secure the ladder in their vehicle had failed to restrain it when the vehicle accelerated after passing the aiming point markings in the touchdown zone.

On 18 December 2018, a Boeing 787-9 was instructed to taxi to a specified remote de-icing platform for de-icing prior to takeoff from Oslo. The aircraft collided with a lighting mast on the de-icing platform causing significant damage to both aircraft and mast. The Investigation found that in the absence of any published information about restricted aircraft use of particular de-icing platforms and any markings, lights, signage or other technical barriers to indicate to the crew that they had been assigned an incorrect platform, they had visually assessed the clearance as adequate. Relevant Safety Recommendations were made.

On 10 May 2019, a Bombardier DHC8-300 taxiing in at Toronto at night was hit by a fuel tanker travelling at “approximately 25 mph” which failed to give way where a designated roadway crossed a taxiway causing direct crew and indirect passenger injuries and substantial damage. The Investigation attributed the collision to the vehicle driver’s limited field of vision in the direction of the aircraft coming and lack of action to compensate for this, noting the need for more effective driver vigilance with respect to aircraft right of way rules when crossing taxiways. The aircraft was declared beyond economic repair.

On 24 April 2005, an Airbus A340-200 landed short of the temporarily displaced runway threshold at Perth in good daylight visibility despite their prior awareness that there was such a displacement. The Investigation concluded that the crew had failed to correctly identify the applicable threshold markings because the markings provided were insufficiently clear to them and probably also because of the inappropriately low intensity setting of the temporary PAPI. No other Serious Incidents were reported during the same period of runway works.

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.

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