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), which 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.
This article links to other SKYbrary articles that reference explicit or implied opportunities to integrate ground-collision countermeasures with those already targeting RIs and REs. It also cites ground collision–relevant cases among actual scenarios analysed because of their relevance to controller detection of occupied runways. Briefs of pertinent accidents and incidents suggested by other SKYbrary articles, relevant References and Further Reading are provided.
The SISG analysed 20 ground safety events comprising RIs (primarily) 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 Ground Handling):
- 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.
- 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 efflux [engine exhaust gases] from large aircraft does 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., taxyways closed due to construction work or recently changed taxiway diagram or signage).