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In March 1977, in what remains the world’s deadliest aviation accident, two passenger jumbo jets collided on a runway at Tenerife, Canary Islands, causing the deaths of 583 passengers and crew. In the U.S., the deadliest U.S. runway incursion accident occurred in August 2006 when Comair flight 5191, a regional jet, crashed after taking off from the wrong runway, killing 49 of the 50 onboard. The worst U.S. runway incursion accident involving two aircraft was a collision between a USAir 737 and a Skywest Metroliner commuter airplane at Los Angeles International Airport in February 1991, which killed 34 people.
As an example of a recent serious incident, in August 2007, at Los Angeles International Airport, a WestJet 737 and a Northwest A320 nearly collided. The WestJet landed and then exited at a taxiway and changed to ground control frequency without authorization while the airplane was holding between the parallel runways. The tower controller cleared the Northwest for takeoff. Meanwhile, the pilot of the WestJet flight contacted ground control and said, "Ground, WJA900 with you on reverse [taxiway] yankee for gate 35." The ground controller assumed that the tower controller had instructed the flight to cross the runway and responded, "WJA900, Los Angeles tower, taxi [via taxiway] echo to the gate." Ten seconds later, the pilot of WJA900 confirmed that the flight was cleared to cross the runway. The ground controller asked who called and the pilot again asked whether or not they were cleared to cross the runway. The ground controller then realized that WJA900 had not been instructed to cross the runway and told the WestJet to stop. The airplane crossed the hold short line but did not enter the runway. The two aircraft missed colliding by 37 feet as the Northwest flight departed. The tower received an AMASS warning when the pilot was confirming to cross and before the controller told the WestJet to stop.
The runway incursion issue has been on the Safety Board’s Most Wanted List since the list’s inception in 1990. In the late 1980s, an inordinate number of runway incursions/ground collision accidents resulted in substantial loss of life, and the Board issued numerous safety recommendations addressing the issue. The Federal Aviation Administration (FAA) has since taken action to inform controllers of potential runway incursions, improve airport markings, and install the Airport Movement Area Safety System (AMASS) and Airport Surface Detection Equipment Model X (ASDE-X). These systems are an improvement, but are not sufficient as designed to prevent all runway incursions. The runway incursion rate in the United States has not appreciably changed over the past 4 years, and stands at about 6.1 runway incursions per 1,000,000 tower operations, despite these improvements.
Information needs to be provided directly to the flight crews as expeditiously as possible to prevent runway incursions. The issue is one of reaction time. Safety Board investigations have found that AMASS is not adequate to prevent serious runway collisions, because too much time is lost routing valuable information through air traffic control. After an AMASS alert, the controller must determine the nature of the problem, determine the location, identify the aircraft involved, and determine what action to take. Only after all of these determinations have been made can appropriate warnings or instructions be issued. The flight crew must then respond to the situation and take action. Simulations of AMASS performance using data from actual incursions show that alerts may occur as little as 8 to 11 seconds before a potential collision. In recent incidents, AMASS did not alert controllers in time to be effective, and the situations were instead resolved by flight crew actions that sometimes bordered on heroics or simple luck.
Until there is a system in place to positively control ground movements of all aircraft, with direct warning to pilots, the potential for this type of disaster will continue to be high.
Air traffic control (ATC) procedures should require specific clearances, rather than rely on implied clearances, for aircraft to cross runways. This requirement would reduce the chance of a runway incursion because pilots would have to obtain an explicit clearance before crossing any runway; without such a clearance, the pilot would be required to hold short. Further, if aircraft need to be cleared to cross multiple runways, controllers should issue an explicit crossing instruction for each runway after the previous runway has been crossed.
Implementation of the Safety Board’s recommendations will reduce the chances of a runway collision between two airplanes, and will also reduce the risk of a pilot mistakenly selecting an incorrect runway as occurred in the Comair flight 5191 accident in Lexington, Kentucky. If the revisions recommended had been implemented before that accident, these procedures would have provided the flight crew with better awareness of the airplane’s position along the taxi route and would have required the controller to visually observe the airplane’s position and monitor the taxi as the airplane progressed toward the departure runway. In addition, research and analysis sponsored by the FAA has cited pilot and controller concerns about the adequacy of runway crossing requirements, and most of these pilots and controllers thought that it would be beneficial to adopt the procedures recommended.
Analysis performed by the Flight Safety Foundation has shown that runway excursions accounted for approximately 29 percent of all accidents involving turboprop and turbojet aircraft worldwide between 1995 and 2006. A runway excursion occurs when an aircraft either overruns or undershoots a runway while landing or taking off. Existing FAA regulations do not specify either the type of arrival landing distance assessment that should be performed or a safety margin that should be applied. The FAA advocates a minimum safety margin of 15 percent for arrival landing distance assessments and a 15-percent factor is included in the European Aviation Safety Agency and Joint Airworthiness Authorities operational requirements for contaminated runway landing performance. The FAA has sought voluntary operator compliance with performing landing distance assessments, and applying a 15-percent safety margin. However, runway overruns continue to occur in the United States when the flightcrews have not performed a landing distance assessment before landing on a contaminated runway.
Summary of Action
In FY 2005, the FAA conducted a study to determine whether a direct warning capability to flight crews could be developed. A solution set with three technology levels was proposed, and simulations were conducted in May 2005 to assess the proposal’s effectiveness. Thirty-six commercial and general aviation pilots participated in simulations of 15 different incursion scenarios. The FAA found that a significant reduction of runway incursion risk was possible. The same year, the FAA initiated field tests of a Runway Status Lights system at the Dallas/Fort Worth International Airport. Initial test results have been promising and the FAA is performing additional testing to determine the extent to which this technology can be applied nationwide. The FAA plans to explore alternative operational and system solutions to address shortcomings with the systems evaluated in the simulation study. The FAA also plans an analysis of a flight deck–based direct warning system.
Although these technologies may offer added safety by providing information directly to cockpit crews, they are many years away from possible national implementation. More than 7 years after this recommendation was issued, the FAA is still evaluating technology, and has not yet developed plans for funding and installing these systems at airports. In view of the very real and continuing threat posed by runway incursions, and the failure of previously developed systems and procedures to reduce the rate of runway incursions, this is not an acceptable response.
The FAA does not agree that ATC should issue an explicit clearance for each runway crossing. The FAA conducted a study that examined runway incursions involving pilot deviations and controller operational errors between September 1, 1998, and December 31, 2002. The study examined approximately 1,300 events, and the FAA concluded that only 28 were relevant to the Safety Board’s recommendations regarding an explicit clearance for crossing each runway. Because the Board was aware of data indicating a considerably higher rate of runway safety problems that might have been prevented by requiring explicit runway crossing clearance, the Board requested that the FAA share the data sources or study results from their analysis. To date, that information has not been provided. The Board is concerned about situations in which pilots may be lost, or believe they have received permission to move to a different position than the one that the controller intended. In these situations, under the current rules in CFR 91.129 and Order 7110.65, the pilot will cross runways along the path without requesting clearance. Thus, simple individual mistakes may have catastrophic consequences.
The FAA has issued voluntary guidance advocating flightcrews performing landing distance assessments, and applying a minimum 15 percent safety margin. Since the FAA issued this voluntary guidance, the Safety Board has continued to investigate accidents and incidents in which aircraft overran the runway while landing on a contaminated runway after the flightcrew did not perform a landing distance assessment.
Action Remaining
Implement a safety system for ground movement that will ensure the safe movement of airplanes on the ground and provides direct warning capability to the flight crews. Implement ATC procedures requiring an explicit clearance for each runway crossing. Require operators to conduct arrival landing distance assessments before every landing based on existing performance data, actual conditions, and incorporating a minimum safety margin of 15 percent.
Safety Recommendations
A-00-66 (FAA)
Issued July 6, 2000
Added to the Most Wanted List: 2001
Status: Open—Unacceptable Response
Require, at all airports with scheduled passenger service, a ground movement safety system that will prevent runway incursions; the system should provide a direct warning capability to flight crews. In addition, demonstrate through computer simulations or other means that the system will, in fact, prevent incursions. (Source: Letter of recommendation dated July 6, 2000, to the FAA addressing runway incursions)
A-00-67 (FAA)
Issued July 6, 2000
Added to the Most Wanted List: 2007
Status: Open—Unacceptable Response
Amend 14 Code of Federal Regulations (CFR) section 91.129(I) to require that all runway crossings be authorized only by specific air traffic control clearance, and ensure that U.S. pilots, U.S. personnel assigned to move aircraft, and pilots operating under 14 CFR Part 129 receive adequate notification of the change.. (Source: Letter of recommendation dated July 6, 2000, to the FAA addressing runway incursions)
A-00-68 (FAA)
Issued July 6, 2000
Added to the Most Wanted List: 2007
Status: Open—Unacceptable Response
Amend FAA Order 7110.65, “Air Traffic Control,” to require that, when aircraft need to cross multiple runways, air traffic controllers issue an explicit crossing instruction for each runway after the previous runway has been crossed. (Source: Letter of recommendation dated July 6, 2000, to the FAA addressing runway incursions)
A-07-57 (FAA) (Urgent)
Issued October 2, 2007 (Superseded A-06-16)
Added to the Most Wanted List: 2007
Status: Open—Unacceptable Response
Immediately require all 14CFR Part 121, Part 135, and Part 91, subpart K operators to conduct arrival landing distance assessments before every landing based on existing performance data, actual conditions, and incorporating a minimum safety margin of 15 percent (Source: Investigation of the runway overrun at Chicago Midway Airport on December 8, 2005, of Southwest Airlines flight 1248, a Boeing 737)
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