U. S. Department of Transportation
Clarification of the Rating of Runway Incursions
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Clarification of the Rating of Runway IncursionsA final word on the ranking system is warranted. In addition to information about factors influencing severity, the deep scrutiny of the ranking system provided insights how incursion severity is ranked. Throughout the results, there were often disparate impacts between conflict and non-conflict events. Factors such as commercial carrier status showed no impact for all severity categories, but when excluding category D events, a relationship with severity emerged. Moreover, only one of the ordered models satisfied the assumptions underlying the ordered logit model – and that model excluded category D events.101 Additionally, the multinomial models reveal that some variables explain category D incursions but none of the conflict categories. All this evidence combines to suggest that category D incursions are a distinct group from the remaining three categories. Furthermore, there is evidence that category D incursions do not follow a smooth ordering with the other three categories. This has implications for any modeling effort that chooses to focus on all severity categories. Any model will need to account for a “two-stage” process, distinguishing between conflict and non-conflict and then attempting to identify severity. This also has implications for understanding the danger posed by any given event. If category D events are not part of a smooth ranking, the current system may not be properly capturing the risk inherent in some category D events. A simplistic example is when an aircraft lands on a runway without clearance or communication with the tower. If another aircraft is present on the runway, the incursion would likely be an A or B; however, if the airport is otherwise empty the same pilot error would be rated a D. This bears serious consideration as, in this example, the behavior in question is inherently quite risky and likely would be a serious event in the presence of other aircraft, someone the pilot could not possibly control. While not informed by rigorous research, the results of this effort would imply that incursion severity is truly (at least) a two-stage process. The first stages relates to the riskiness of a behavior (landing on a closed runway or forgetting an aircraft on the airfield versus stopping one foot past a hold-short line or giving a clearance to cross a runway to a non-existent flight number). The second stage relates to the likelihood that another aircraft will be nearby when the incident occurs. That is, the axes would be the riskiness of the behavior and the possibility of a conflict. Changes to the ranking system would require significant involvement by many players at the FAA and ICAO, but such coordination may offer a considerable benefit in an effort to respond to safety risks. Those interested in using data on incursions to reduce the likelihood of future collisions need to take a serious look at how to best classify incursions along however many axes of risk are most appropriate to model.
This is an excerpt from the Manual on the Prevention of Runway Incursions, First Edition.102 It is reproduced unedited from that document. Chapter 6 CLASSIFICATION OF THE SEVERITY OF RUNWAY INCURSIONS 6.1 SEVERITY CLASSIFICATION 6.1.1 The objective of runway incursion severity classification is to produce and record an assessment of each runway incursion. This is a critical component of risk measurement, where risk is a function of the severity of the outcome and the probability of recurrence. Whatever the severity of the occurrence, however, all runway incursions should be adequately investigated to determine the causal and contributory factors and to ensure risk mitigation measures are implemented to prevent any recurrence. 6.1.2 Severity classification of runway incursions should be assessed as soon as possible after the incident notification with due regard for the information required in 6.2. A reassessment of the final outcome may be applied at the end of the investigation process. 6.1.3 For the purpose of global harmonization and effective data sharing, when classifying the severity of runway incursions, the severity classification scheme in Table 6-1 should be applied. See Figure 6-1 for examples of severity classification. Table 6-1. Severity classification scheme
6.2 FACTORS THAT INFLUENCE SEVERITY To properly classify the severity of a runway incursion the following information is required: a) Proximity of the aircraft and/or vehicle. This distance is usually approximated by the controller or from the aerodrome diagram. When an aircraft flies directly over another aircraft or vehicle, then the closest vertical proximity should be used. When both aircraft are on the ground, the proximity that is used to classify the severity of the runway incursion is the closest horizontal proximity. When aircraft are separated in both horizontal and vertical planes, the proximity that best represents the probability of collision should be used. In incidents in which the aircraft are on intersecting runways, the distance from each aircraft to the intersection is used. b) Geometry of the encounter. Certain encounters are inherently more severe than others. For example, encounters with two aircraft on the same runway are more severe than incidents with one aircraft on the runway and one aircraft approaching the runway. Similarly, head-on encounters are more severe than aircraft moving in the same direction. c) Evasive or corrective action. When the pilot of an aircraft takes evasive action to avoid a collision, the magnitude of the manoeuvre is an important consideration in classifying the severity. This includes, but is not limited to, hard braking action, swerving, rejected take-off, early rotation on take-off, and go-around. The more severe the manoeuvre, the higher its contribution to the severity rating. For example, encounters involving a rejected take-off in which the distance rolled is 300 metres are more severe than those in which the distance rolled is less than 30 metres. d) Available reaction time. Encounters that allow the pilot little time to react to avoid a collision are more severe than encounters in which the pilot has ample time to respond. For example, in incidents involving a go-around, the approach speed of the aircraft and the distance to the runway at which the go-around was initiated needs to be considered in the severity classification. This means that an incident involving a heavy aircraft aborting the landing and initiating a go-around at the runway threshold is more severe than one that involves a light aircraft initiating a go-around on a one-mile final. e) Environmental conditions, weather, visibility and surface conditions. Conditions that degrade the quality of the visual information available to the pilot and controller, such as poor visibility, increase the variability of the pilot and controller response and, as such, may increase the severity of the incursion. Similarly, conditions that degrade the stopping performance of the aircraft or vehicle, such as wet or icy runways, should also be considered. f) Factors that affect system performance. Factors that affect system performance, such as communication failures (e.g. “open mike”) and communication errors (e.g. the controller’s failure to correct an error in the pilot’s readback), also contribute to the severity of the incident. 6.3 RUNWAY INCURSION SEVERITY CLASSIFICATION CALCULATOR A runway incursion severity classification (RISC) calculator is available on CD (see Appendix H for a description). The calculator was developed to assist States in assessing the severity of runway incursion events. Use of the RISC calculator should also enable a consistent assessment to be made. Alternatively, the severity of runway incursions can be classified manually using the guidance contained in 6.1 and 6.2. 
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