Runway Incursions: Causes, Risk Factors, and Aviation Safety

Introduction and Background

Today, commercial aviation is widely recognized as the safest form of mass transportation by far, and the aviation industry's safety track record is unparalleled in other sectors. Moreover, innovations in avionics have made air transportation even safer than in the recent past, and current signs indicate these trends will continue well into the foreseeable future. Nevertheless, the potential for runway incursions to cause catastrophic air disasters is always present, and the natural and human sources of these incidents are virtually infinite. In this regard, the U.S. Federal Aviation Administration (FAA) defines a runway incursion as "any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of a surface designated for the landing and takeoff of aircraft" (Runway incursions, 2020, para. 2).

Runway incursions can also be caused by foreign object debris (FOD) and bird (and other animal) strikes, which are far more commonplace than many air travelers might believe. According to Mrazova (2014), "Bird strikes are innocuous. A large airport suffers one bird strike every three days. 92% of most strikes cause no damage, but the average cost still comes to $22,741 per strike. Another fact is that 41% of all bird strikes occur on the runway. Of these, up to 50% are caused by birds actually sitting on the runway rather than simply flying past" (p. 75).

Airport managers around the world have taken extreme measures in an effort to ward off birds and other animals, but nature is unpredictable and the potential for this source of runway incursions is especially challenging to mitigate. According to the Flight Safety Foundation (2020), "Animal strikes accounted for one fatal accident in the past five years. This category includes conflicts with birds, primarily on takeoff and during approach and landing, and conflict with terrestrial animals on the ground during the takeoff roll or landing. In 2015, the most recent year for which data are available, a record 13,795 wildlife strikes were reported to the [FAA]" (Key safety issues, para. 2). Surface incidents involving animal strikes or humans are defined by the FAA as "an unauthorized or unapproved movement within the designated movement area (excluding runway incursions) or an occurrence in that same area associated with the operation of an aircraft that affects or could affect the safety of flight" (Runway incursions, 2020, para. 3).

Taken together, it is clear that commercial aviation in general and the American flying public in particular remain at significant risk from severe runway incursions from multiple sources that have the potential to cause catastrophic results.

Problem Statement

Despite aggressive efforts to address the numerous antecedent causes of runway incursions, these incidents continue to occur on a regular basis (Torres & Metscher, 2011). Singh and Meier (2009) emphasize that "preventing runway incursions and conflicts is amongst the most critical problems in airport ground movement operations. Despite being on the NTSB's 'Most Wanted' list of desired safety improvements for over a decade now, it remains a persistent issue" (p. 653). Indeed, there are several runway incursion incidents globally every day, and the numbers continue to increase — albeit more slowly than in the past (Singh & Meier, 2009).

Notwithstanding the progress that has been made to date in reducing the number of runway incursions, collisions on the magnitude of the air disasters that occurred in Tenerife in 1977 and Milan in 2001 are extremely rare; however, the potential for runway incursions to cause similar disasters is always present (Squire & Barrow, 2010). Moreover, even less severe categories of runway incursions can have severe economic consequences. According to Squire and Barrow (2010), "In 2005, there were 63.1 million flights in the United States, with a rate of 5.2 runway incursions per million flights. The comparable figures for 2007 were 61.1 million flights and 6.1 runway incursions per million flights" (p. 10).

In some cases, the causes of runway incursions are foreseeable but unpredictable — such as bird strikes or disoriented humans wandering onto a taxiway — while other causes have already been identified but remain unresolved (Schönefeld & Möller, 2012). As Mrazova (2014) notes, "The risk of a runway incursion is still a serious problem. Fortunately, this problem has been exhaustively studied by dozens of experts and many mitigating processes have been applied" (p. 71). The wide array of mitigating processes implemented in recent years underscores the harsh reality that there is no "one-size-fits-all" solution to runway incursions caused by unpredictable man-made and natural occurrences.

It is especially noteworthy that some mitigation initiatives have been effective in part due to the severely diminished air travel caused by restrictions imposed by national governments in response to the ongoing Covid-19 global pandemic. Absent this decrease in air travel, it is reasonable to posit that the recent declines in runway incursions would not have occurred; rather, the same antecedent challenges that have historically contributed to runway incursions would have been further exacerbated. Johnson and Zhao (2016) advised pre-pandemic that "owing to the growing traffic volume and airport expansion, avoiding runway incursions has become a critical issue for aviation safety. Increased traffic volume could be considered as one of the most significant drivers of runway incursions" (p. 16).

Beyond those challenges, some other issues continue to adversely affect the safety of the nation's airports, including the outdated designs of some airports' runways and taxiways. Johnson and Zhao (2016) add that "owing to legacy configurations of runways and taxiways, the risk of runway incursion has increased along with the growing traffic volume and aircraft size, especially for airports designed and constructed before the jet age" (p. 16). This problem is readily understandable given the significant costs involved in constructing and maintaining even modest airport facilities, but outdated facilities can exacerbate human errors in ways that transform near-misses into outright aircraft collisions with corresponding human and economic costs.

In sum, runway incursions are a threat to aviation safety that demand increased attention and collaborative efforts from public and private sector partners alike.

Review of Relevant Literature

The study draws on a combination of primary and secondary sources, including relevant U.S. governmental statistical data, analytical reports, field studies, peer-reviewed journal articles, empirical observations by aviation industry safety practitioners, and other scholarly resources. The goal is to identify opportunities for improvement and further reduction in the incidence of runway incursions at American airports.

The primary sources for the literature review were resources provided by the FAA, the National Transportation Safety Board (NTSB), and other U.S. government aviation authorities, as well as international aviation safety organizations. These were supplemented by peer-reviewed studies providing original research concerning strategies for mitigating runway incursions.

A macro overview of the research on runway incursions indicates that a growing body of scholarly literature addresses the different variables contributing to their incidence and the steps taken to address them (Wilke & Majumdar, 2010). One overarching factor consistently demonstrated to contribute to runway incursions — and one that defies easy solutions — is human error.

An analysis of the relevant literature revealed that human error accounts for the majority of all runway incursions by far. The primary sub-variables affecting the extent to which human error results in runway incursions include the type and recentness of training provided to air crews and air traffic controllers, as well as the level of air traffic occurring at any given time. Working conditions and scheduling are also implicated in the types of human errors that cause runway incursions.

In any workplace setting, adequate training is an essential ingredient for success, but the life-and-death circumstances involved in getting an aircraft from point A to point B are vastly different from most enterprises. When air traffic controllers and air crew members lack the training they need to operate an airport safely, runway incursions are inevitable. Likewise, overworked and fatigued personnel are far more likely to make mistakes that can cost human lives, making optimal scheduling and personnel staffing absolutely essential for minimizing runway incursions.

A study by Johnson et al. (2017) identified a statistically significant relationship between the configuration of airport runways and taxiways and the incidence and severity of runway incursions. The methodology of this study and the findings that emerged from the analysis are presented in the Findings section below.

Besides legacy design constraints, another consistent sub-variable identified in the research is a fundamental lack of resources from cash-strapped municipalities and local governments. Because resources are by definition scarce, outdated airport facilities and taxiways represent one area where a real difference can be made by focusing available resources appropriately. As Mrazova (2014) explains:

"Constantly reducing the likelihood of airplanes colliding with obstructions on airport runways — whether they are other aircraft, vehicles, individuals, or wildlife — is the primary objective of the [aviation safety groups]. In this case, we must focus our limited resources on the causal factors with the highest risk of contributing to the likelihood of significant safety events. Therefore, the ways of reducing runway incursion risks are very important." (p. 72)

While it is possible to minimize the impact of human error on runway incursions through optimal scheduling and ongoing training opportunities, it is impossible to completely eliminate this threat without allocating additional resources. A study by Mathew and Major (2010) concluded that "budget is always a constraint for airport improvements, so it is important to have systematic methods to prioritize resource allocation and identify which technologies to invest in" (p. 16). Furthermore, the lack of resources exacerbates the ability of airport managers and the federal government to provide adequate scheduling and training, and qualified, experienced air traffic control personnel are becoming increasingly scarce. The combination of these factors underscores the need for innovative strategies to help protect the flying public and ensure that commercial aviation continues to represent the safest form of mass transportation in the future.