Runway Incursion Prevention: Keeping Airports Safe

On March 27, 1977, two Boeing 747s collided on the runway at Los Rodeos Airport (now Tenerife North, Spain) in dense fog. KLM Flight 4805 had begun its takeoff roll while Pan Am Flight 1736 was still taxiing on the same runway. The collision killed 583 people — the deadliest accident in aviation history. The tragedy was caused by a chain of factors including miscommunication, fog, and the absence of ground radar, but at its core was a runway incursion: an aircraft on the runway without clearance while another was using it for takeoff. Nearly five decades later, runway incursions remain one of the most serious safety concerns in aviation, and the systems designed to prevent them have become among the most sophisticated technologies deployed at airports.

What Is a Runway Incursion?

The 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." This includes pilots taxiing onto a runway without clearance, ground vehicles crossing a runway without authorization, and pedestrians walking onto runway surfaces. The ICAO uses a similar definition.

Runway incursions are classified by severity. Category A is the most serious: a conflict that required extreme action to avoid a collision, or where a collision occurred. Category D is the least serious: an incursion that posed no immediate safety threat. The FAA reports over 1,700 runway incursions annually in the United States, the vast majority Category D. But even a single Category A event can result in catastrophe, as the Tenerife disaster demonstrated.

A runway incursion at JFK Airport (JFK) on January 13, 2023, illustrated how close calls continue to occur at even the most heavily monitored airports. A Delta Air Lines Boeing 737, cleared for takeoff on Runway 4L, came within approximately 300 meters of an American Airlines 777 that had crossed the runway without clearance. The incident, classified as Category A by the NTSB, prompted renewed urgency around runway safety technology deployment.

Common Causes of Runway Incursions

Analysis of runway incursion data reveals recurring patterns. Pilot deviations — the largest category — include taxiing onto a runway without clearance, crossing a runway hold position marking without authorization, and taking off or landing on the wrong runway. These errors are most common at unfamiliar airports, during nighttime or low-visibility conditions, and at airports with complex taxiway geometries where it is easy to become confused about one's position.

Controller errors — issuing a clearance that creates a conflict, or forgetting that an aircraft or vehicle is on the runway — account for another significant category. Controller workload is a factor: during peak operating periods at busy airports, a single controller may be managing dozens of aircraft and vehicles on the surface simultaneously, and momentary lapses in situational awareness can result in conflicting clearances.

Vehicle and pedestrian deviations — ground vehicles or airport workers crossing a runway without authorization — are less frequent but can be equally dangerous. Construction vehicles, wildlife management teams, and airport maintenance crews all operate on or near runways, and procedures for coordinating their movements with ATC are critical.

Surface Detection Equipment: Eyes on the Runway

The most significant technological response to runway incursions has been the deployment of surface detection and surveillance systems that give controllers a real-time picture of all aircraft and vehicles on the airport surface. The FAA's ASDE-X (Airport Surface Detection Equipment, Model X) system, deployed at 35 of the busiest US airports, combines surface radar, multilateration sensors, and ADS-B data to display the position and identity of every transponder-equipped target on the airport surface on the controller's screen.

ASDE-X incorporates safety logic that generates automatic alerts when a potential conflict is detected. If an aircraft is on a runway and another aircraft or vehicle is approaching the same runway, the system generates a visual and audio alert on the controller's display. The controller can then issue instructions to resolve the conflict before it becomes dangerous.

EUROCONTROL has deployed A-SMGCS (Advanced Surface Movement Guidance and Control System) at major European airports, providing similar functionality: surface surveillance, identification, routing guidance, and conflict detection. Frankfurt (FRA), Paris CDG, Amsterdam Schiphol (AMS), and London Heathrow (LHR) all operate A-SMGCS systems.

Visual Aids and Surface Markings

Technology is only one layer of runway incursion prevention. The physical design and marking of the airport surface play an equally important role. Runway hold position markings — painted pairs of solid and dashed yellow lines perpendicular to the taxiway at every runway intersection — are the most critical ground markings at any airport. No aircraft or vehicle may cross these markings without explicit ATC clearance. Pilots are trained to treat the hold position as an absolute boundary: stopping short is mandatory; crossing without clearance is a violation.

Enhanced taxiway centerline markings, which add yellow dashes to the standard centerline leading up to a runway intersection, alert pilots that they are approaching a runway. Runway guard lights — alternating yellow flashing lights installed at hold positions — provide a visual warning that is effective even in poor visibility or at night. Some airports have installed in-pavement runway status lights (RWSL) that illuminate red when a runway is active (an aircraft is departing or arriving) and turn off when the runway is clear.

The FAA's Final Approach Runway Occupancy Signal (FAROS) system causes the PAPI lights (the visual glide slope indicators on the runway approach) to flash when the runway is occupied, alerting arriving aircraft that the runway is not clear. The system is installed at a growing number of US airports and provides a final layer of warning visible to the arriving crew.

Training and Procedural Measures

Technology and physical infrastructure address the consequences of human error; training and procedures aim to prevent the errors themselves. Crew Resource Management (CRM) training emphasizes communication, cross-checking, and situational awareness during ground operations. Sterile cockpit procedures, originally developed to reduce errors during takeoff and landing, have been extended to include taxi operations at many airlines — requiring pilots to minimize non-essential conversation and focus on navigation during surface movement.

Standard phraseology is a critical procedural defense. ICAO and the FAA have established precise language for runway clearances: "cleared for takeoff" and "cleared to land" are the only phrases that authorize runway use. The word "takeoff" is otherwise avoided in ATC communications to prevent confusion — controllers say "departure" instead. The word "cleared" is restricted to authorizations that involve a runway. These conventions exist specifically because of historical incidents where ambiguous communication contributed to runway incursions.

The "line up and wait" instruction (used by the FAA; ICAO uses "line up and wait" as well, replacing the previous "taxi into position and hold") directs an aircraft to enter the runway and await takeoff clearance. This instruction is inherently high-risk because it places an aircraft on an active runway before clearance to depart. Controllers must carefully manage the sequence to ensure no arriving aircraft will reach the runway threshold before the waiting aircraft receives its takeoff clearance and begins rolling.

Airport Design for Runway Safety

Airport geometry significantly affects runway incursion risk. Airports where taxiways cross active runways — requiring aircraft to cross a runway to reach gates or departure runways — have inherently higher risk than airports where the taxiway system allows aircraft to move between all areas without crossing a runway. When airports are redesigned or expanded, eliminating runway crossings is a priority.

Atlanta (ATL) benefits from a parallel runway and taxiway layout where most aircraft movements do not require runway crossings. Chicago O'Hare (ORD), by contrast, has a complex intersecting runway layout that requires frequent runway crossings — a geometry being addressed by the ongoing $8.5 billion O'Hare Modernization Program, which is reconfiguring the runway system to reduce crossings.

Perimeter taxiways — taxiways that route aircraft around the end of a runway rather than across it — are another design solution. By providing an alternative path that avoids the runway entirely, perimeter taxiways eliminate the need for runway crossing clearances. The FAA has funded perimeter taxiway construction at numerous airports as a safety improvement.

The Future of Runway Incursion Prevention

Emerging technologies promise further improvements. Cockpit display of traffic information (CDTI) — showing pilots a real-time map of all traffic on the airport surface on their cockpit screens — gives crews the same situational awareness that surface detection systems provide to controllers. Electronic flight bags (EFBs) with moving-map displays of the airport surface are already standard at most airlines and have measurably improved crew awareness of their position relative to runways.

Artificial intelligence and machine learning are being applied to surface safety prediction — analyzing patterns in surface traffic to identify high-risk situations before they develop. If the system detects that a particular runway intersection has elevated incursion risk during certain traffic patterns (for example, when multiple aircraft are taxiing toward the same hold point simultaneously), it can proactively alert the controller.

The ultimate goal is zero runway incursions. The industry has not yet achieved that goal, and the irreducible complexity of airport surface operations — dozens of aircraft and vehicles moving simultaneously on intersecting paths, in all weather conditions, under time pressure — means that human error will continue to occur. But the layered defenses now in place — technology, training, procedures, airport design, and organizational culture — have reduced the risk of a Tenerife-scale catastrophe to a level that would have seemed impossible in 1977. The work of runway safety is never finished, but it is working.