U. S. Department of Transportation
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- Background
- Fiscal Year 2008
- Fiscal Year 2009
- Fiscal Year 2010
- Fiscal Year 2011
- FAA Response to Runway Incursions
- Method of Investigation
IntroductionThe focus of this research is to examine the underlying factors that contribute to the severity of runway incursions. A runway incursion is an event in which a person, vehicle, or aircraft enters the runway safety area without authorization. From the perspective of the FAA, runway incursions represent dangerous pre-collision behavior. In accordance with standards established by the International Civil Aviation Organization (ICAO), runway incursions are ranked according to their severity, with category D being the least dangerous and category A being a narrowly avoided collision.1 As it is believed that reducing the severity of incursions reduces the likelihood of having a collision, it is important to understand those factors that influence incursion severity. Previous research has focused on qualitative examinations of incursion reports. Case studies were used to understand some trends and identify common causes. The research detailed in this report does not seek to explain the causes of particular events, but rather focuses on broader trends in incursion severity. Understanding those patterns can provide insight into policy-making and identify areas for future research.
Runway incursions are classified in two main ways. Severity is ranked from category D to category A. In addition to that ranking is a classification of who was at fault for the incident: controller at fault, called operational errors (OEs); pilot at fault, called pilot deviations (PDs); and vehicle or pedestrian at fault, called vehicle or pedestrian deviations (V/PD). In fiscal year 2008, FAA adopted a new definition of runway incursions, conforming to ICAO standards.2 When compared to previous years, the new definition produces more runway incursions, even with no change in underlying behavior or safety. Thus, any comparison with previous years needs to be done so in the light of the changing definitions. However, this definitional change does not reclassify any severe incursions (class A or B). Below is an overview of recent incursion trends to provide context for the research that follows. Fiscal Year 2008During FY 2008, there were 1,009 runway incursions.3 Twenty-five of those incursions were classified as severe (category A or B), resulting in a rate of approximately 0.43 severe incursions per million operations (takeoff or landing). The overall rate of runway incursions was 17.2 incursions per million operations. Fiscal Year 2009During FY2009, there were 951 runway incursions.4 Of those incursions, 12 were categorized as severe, representing a rate of 0.23 severe incidents per million operations. The overall rate of runway incursions was 18 incursions per million operations. Fiscal Year 2010There were 966 incursions during fiscal year 2010, representing a rate of approximately 18.9 incursions per million operations.5 Of those, 6 were categorized as severe, representing a rate of 0.12 severe incidents per million operations.6 Fiscal Year 2011There were 954 incursions during fiscal year 2011, representing a rate of approximately 18.8 incursions per million operations. Of those, 7 were categorized as severe, representing a rate of 0.14 severe incidents per million operations. Runway Incursion TrendsCompared to the previous year, FY2010 saw an increase in both the number of incursions and the rate of runway incursions. However, the number of incursions in FY2010 is still below the FY2008 total of 1009 incursions. The incursion rate has increased in general from 2008 (a rate of 17.2 incursions per million operations) to 18.9 incursions per million operations in FY2010. FY2011 saw the rate remain almost constant, though there was a slight drop in total number of incursions. FY2010 saw a continued decrease in the overall number of severe incursions. The rate of severe incursions has also declined. This is contrary to the trend in the overall rate and count of runway incursions. FY2011 saw an increase in both the rate and total number of severe incursions. However, both were very slight and likely not representative of an increasing trend. FAA Response to Runway IncursionsFAA has recently placed a renewed focus on runway safety, starting with a Call to Action in August 2007. A plan “focused on changes in cockpit procedures, airport signage and markings, air traffic procedures, and technology” was developed.7 Further deployment of systems such as ASDE-3/AMASS and ASDE-X will increase controller awareness of movement areas. FAA has also begun deployment of runway status lights at 23 airports. The new light system “gives pilots a visible warning when runways are not safe to enter, cross, or depart on”.8 The first lights are already online with the full set expected to be in service by 2016.9 Yet another effort to reduce runway incursions is the deployment of the Final Approach Occupancy Signal (FAROS) system. The FAROS system “activates a flashing light visible to aircraft on approach as a warning to pilots when a runway is occupied and hazardous for landing” – essentially the arrival counterpart to runway status lights.10 These interventions by FAA are an attempt to control some of the causes and impacts of runway incursions. FAROS and runway status lights are designed to give pilots more information so that they can avoid a runway incursion (by performing a go around or stopping at the hold short line, for example). The ground surveillance technologies (ASDE-3/AMASS and ASDE-X) help improve situational awareness for controllers and provide controllers with early warnings of potential collisions. Both are human factors improvements meant to mitigate runway incursion risk.
The goal of this research was to use statistical methods to identify trends in runway incursion severity. The basis of this research was the set of all incursions that occurred between January 1, 2001 and September 30, 2010. During this time period, there were approximately 8,800 incursions. The methodology focused on analyzing these 8,800 incursions and detecting patterns in airport, aircraft, controller, and pilot characteristics. Additional information on weather was included where feasible. The analysis was effectively split into two parts. The first part was focused on one-way and two-way descriptive statistics and analyzing cross tabulations of variables. As much of the information describing the incursion was categorical in nature, this provided an effective means of analyzing these variables. Additionally, this allowed a wider array of variables to be tested. These results focus on comparing variables pairwise, so are less able to account for interactions. To counteract some of the limitations of the cross tabulation approach, a modeling effort was undertaken. This allowed multiple variables to be included at once and their interactions to be understood. However, as this was a more time-intensive process, the sample had to be limited. It was decided to focus on controller incursions. Thus, the cross tabulations examine many more variables across and broader array of incursion types while the modeling effort attempts to delve deeper into the relationship between these variables and severity within a limited sample. Again, due to time and resource constraints, these models should be considered preliminary only; a more intensive modeling exercise would provide significant improvements to the understanding of runway incursion severity. The modeling effort focused on discrete choice models. Due to the apparently ordered nature of the rankings, an ordered logit model was presumed to be the appropriate model. Evidence suggests, however, that the assumptions of the ordered model did not hold. Therefore, multinomial logit models were employed to capture a more nuanced look at the impacts on severity.
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