Unplanned contact between aircraft while on an airport runway or inadvertent contact between an aircraft and a ground vehicle, pedestrian, obstruction or animal while on an airport runway.
The world’s most deadly aviation accident, the collision of two fully loaded Boeing 747’s, occurred in 1977 on a foggy runway at Tenerife Airport, Canary Islands. In this incident, the captain of a KLM jumbojet, in a hurry to take off and suffering from a profound loss of situation awareness, accelerated down the runway directly into a Pan American jet taxiing in the opposite direction. In the ensuing carnage, 583 people were killed and nearly all of the survivors were injured to a significant degree.
The threat of runway collisions has increased along with the growth of air travel around the world. Since World War II, commercial aviation has steadily grown, dramatically so during most of the 1990’s. In the United States, air travel grew four times more quickly than any other form of ground transportation, pushed by the introduction of jet aircraft into commercial service on a large scale in the early 1960’s. By the year 2000, some 600,000 pilots had made almost 70 million takeoffs and landings at 450 different American airports. Alarmingly, the rate of runway collisions, incidents, and near-misses has exceeded the rate of growth of air travel, even throughout the 1990’s, exhibiting a 75 percent increase between 1993 and 1999, according to the Federal Aviation Administration (FAA).
Despite unparalleled airline passenger volume growth, the actual number of runways in the United States has diminished during this time, due, in large part, to extremely strict noise and environmental pollution regulations. As a result, more operations have been crowded onto fewer runways, taxing the abilities of pilots and air traffic controllers alike. This situation remains largely unresolved, with a particularly hazardous combination of large, complex airports and inexperienced pilots, who are common during times of industry growth.
Except for the rare instance of an aircraft colliding with an animal crossing a runway, the cause of most runway collisions is human error, on the part of pilots, air traffic controllers, or a combination thereof. Such collisions are said to involve human factors.
Air traffic controllers have the primary responsibility of providing safe separation for all forms of traffic at large, busy airports. On infrequent but regular occasions, controllers fail in this mission, due to workload, loss of situation awareness, faulty procedure design, or simple short-term memory loss. Such was the case in 1991 at Los Angeles International Airport, where a USAir 737 landed on top of a Skywest turboprop commuter, which had been directed by a controller to stop on a dark runway awaiting clearance for takeoff. Momentarily distracted by a third aircraft, the controller then cleared the USAir jet to land, without ever directing the Skywest aircraft to take off. Thirty-four people died in the resulting collision.
For both pilots and air traffic controllers, two elements contribute heavily to human-factor errors: a loss of situation awareness and miscommunication. Loss of situation awareness occurs when perception and reality are incongruent, especially with regard to location. To a large degree, this is due to poor or zero visibility, because sight is by far the most dominant sense. With impaired vision, usually due to darkness, fog, obstruction, or sun glare, the ability of pilots and controllers to develop a mental picture of the locations of all relevant aircraft and vehicles is significantly decreased. This leads to participants acting on imperfect information, which, in aviation, can have deadly consequences.
Communication problems repeatedly cause human-factor errors. Except in infrequent instances, in which light-gun signals are used, all operational aviation is coordinated by radio. The quality of radio communications on the frequencies used in aviation is markedly inferior to that of other forms of electronic communication, such as telephone or television, and is subject to static, interference, garble, and outright transmitter or receiver failure. Difficulties can also arise from controllers speaking at a rapid-fire rate, from pilots’ unfamiliarity with an airfield, from passengers or crewmembers asking questions of the pilot, and from poorly marked taxiways. The opportunity for misunderstanding is multiplied when controllers and pilots do not speak the same native tongue, forcing one or both of them to speak a second language.
In-flight safety has improved steadily since World War II, to the extent that, according to the FAA, ground operations have become the most dangerous phase of flight. With this in mind, and with the memory of the Tenerife disaster still fresh, FAA officials aggressively attacked the issue of runway safety throughout the 1990’s. In 1991, 1995, and again in 1998, the FAA developed action plans to address specific issues relating to safer ground operations. The agency also made the reduction of runway accidents and incidents its highest priority, with the goal of markedly reducing occurrences each year. To this end, the National Runway Safety Program Office, formerly known as the Runway Incursion Program Office, was created in 1996 as part of the FAA to focus and coordinate resources and efforts. Four areas were targeted for improvement: management and procedures, airport signs and surface markings, technology, and runway incursion awareness efforts.
Recognizing that confusion, usually due to miscommunication or complex instructions, was often a root cause of runway safety incidents, the FAA took steps to clarify the instructions provided to pilots and required more confirmations from pilots of critical elements of information. Additionally, new restrictions were placed on pilots conducting land and hold-short operations, air traffic control procedures used to expedite the flow of arriving and departing aircraft at airfields with intersecting runways.
Another effort to reduce confusion and to increase situation awareness was to develop more visible and easily recognizable airport signage and markings. Hold-short lines on a taxiway mark the limit of travel toward a runway with specific clearance to cross or enter it. It is essential that these lines are easily seen and recognized. The FAA mandated that all airports double the size of these lines and provide a black background to improve contrast and visibility. In cooperation with the Aircraft Owners and Pilots Association, the FAA examined the possibility of using an anamorphic projection, or unequal magnifications along two perpendicular axes, to create a sort of three-dimensional painted hold-short line. The FAA also examined the possibility of using a stop light system, similar to those used at European airports, to prevent inadvertent runway incursions.
The FAA has invested heavily in technology improvements to solve runway safety problems. Because many problems arise when controllers cannot readily see the aircraft and vehicles they are controlling, typically in fog, snow, or dark conditions, beginning in the early 1990’s, contracts were issued for the development of a ground-scan radar system. This project combined what is essentially a land-oriented version of air traffic control radar with a sophisticated software system called the Airport Movement Area Safety System (AMASS). The system was designed to be used at large airports to automatically alert controllers to impending conflicts in enough time for corrective actions to be taken. Initial results were disappointing. The system was labeled as being over budget, over schedule, and ineffective, criticisms leveled at the FAA on a number of projects during this period. The first AMASS unit was installed at San Francisco, California, in September, 2001, with thirty-three other airports to follow. A simpler and less costly version, ASDE-X, was to be provided to smaller airports, but most U.S. airports would not benefit from either program.
The FAA has long recognized that training and education are effective ways to address human-factors issues, and that policy was extended to the runway collision problem. Reaching air traffic controllers was relatively easy, because they are almost all FAA employees and could thus be scheduled for training as necessary. Controllers received training on new equipment, were educated about the scope and scale of the runway safety problem, and were taught new techniques to address specific issues, especially those involving communication and clarity.
Addressing human-factors issues with the 600,000 pilots utilizing U.S. airports was a more difficult task. Airline pilots could be provided relevant education by their corporate training departments, but teaching general aviation pilots, who constitute the bulk of active aviators in the United States, was more challenging. Taking advantage of the requirement that pilots obtain refresher training every two years, the FAA encouraged flight instructors to promote heavily runway safety awareness. Student pilots received similar instruction as part of their initial training. Through newsletters, safety seminars, and booths at aviation conventions, the FAA spoke directly to pilots on the subject of runway safety. The FAA was aided in this effort by nonprofit aviation organizations, such as the Air Safety Foundation and the Flight Safety Foundation, whose missions are to improve the safety of all forms of air transportation.
Part of the FAA’s agenda was to step up enforcement actions. Increasingly, pilots found there was no such thing as an inconsequential runway incursion. Violations were met with fines, pilot certificate suspensions, or mandatory retraining. Repeat or flagrant offenders could expect more than one of the aforementioned actions.
The FAA, flight instructors, and the nation’s aviation schools identified a number of steps that pilots could take to reduce the possibility of a runway safety compromise.
The first step was to increase visibility. It was recommended that pilots use rotating beacons, landing and taxi lights, and strobe lights while operating on the airport surface, even in the daytime. The degree of illumination should be based on environmental conditions.
A second step involved communications. Unclear or ambiguous instructions should be clarified so that both pilots and air traffic controllers achieve a shared mental model of the situation. Critical elements of information must be repeated back to the controller to ensure that a message has not only been heard but also understood. A sterile cockpit, that is, one in which no extraneous conversation takes place in the presence of the crew, is vital for keeping a cockpit free of distractions.
A third step recommended that pilots taxi accurately. This is best achieved by the pilot having in hand an airport diagram, essentially a road map of the airfield, while the taxi is underway. If a diagram is not available or uncertainty still exists, a “progressive taxi,” involving turn-by-turn sequential instructions from a ground controller, may be requested.
Pilots should also know and abide by taxiway and runway markings and signs. Airport signs and markings are standardized throughout the United States, making this job easier.
Pilots should always confirm runway alignment. More than one pilot has landed or taken off on the wrong runway, creating an obvious safety hazard. This error can be remedied by confirming the runway number and cross-checking with the compass.
Lastly, a pilot’s most important actions should always be to look, listen, and talk. Communication helps all flight participants achieve a shared mental model that is vital to situation awareness.
ASF Runway Safety Program. (www.aopa.org/asf/runway_safety/). Part of the Air Safety Foundation effort to reduce runway accidents by providing highly relevant operational pilot information, this Web site features a three-module, interactive program designed to teach pilots about runway safety Craig, P. A. The Killing Zone: How and Why Pilots Die. New York: McGraw-Hill, 2001. An analysis of National Transportation Safety Board investigations of all types of aircraft accidents, written for pilots and nonpilots alike and providing detailed explanations of trends and human-factors issues. Gero, D. Aviation Disasters. 3d ed. Somerset, England: Patrick Stephens, 2000. An encyclopedia of every commercial aviation crash that took at least eighty lives. An excellent source of reference information, illustrated with diagrams and photographs.
Airline industry, U.S.
Federal Aviation Administration
National Transportation Safety Board
Pan Am World Airways
Training and education