Danger: Airplane Crossing

Controlling airplanes on the ground is a thornier problem than controlling them in the air.

Who's at fault when airplanes cross paths where they're not supposed to? Controllers, pilots, and even the Federal Aviation Administration share the blame. (Paul Dimare)
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One of the deadliest runway incursions in the United States occurred at LAX in 1991. A harried controller burdened with a broken ground radar, trying to do multiple jobs and distracted by a search for paperwork, cleared a USAir Boeing 737 to land on the runway where a Skywest Metro commuter flight awaited takeoff. Twenty-two people were killed. NTSB investigators blamed the FAA for designing an air traffic control system that depended unrealistically on “flawless human performance” at busy airports and said that system designers shared responsibility for the disaster.

Ever since, the NTSB has urged the FAA to develop an automated system to detect potential incursions that controllers and pilots missed. The FAA tried. But its Airport Movement Area Safety System, or AMASS, turned into a case study of why runway incursions are so hard to avoid.

While computers can spot airplanes flying on a collision course, they have a harder time predicting that a pilot is about to make a sudden wrong turn onto a runway-—or fail to stop in the right place. By 1999, with the warning system more than doubling in cost from the original $60 million price tag, the FAA said it could not keep aircraft from straying onto runways but would try instead to identify those airplanes likely to collide.

When an Air China 747 taxied onto a runway where a Korean Air 747 was taking off at Chicago’s O’Hare International in 1999, AMASS sounded an alarm in the tower only six seconds before the airplanes would have collided. Controllers had too little time to identify the airplanes involved, contact the pilots, and tell them what to do. The Korean Air pilot spotted the other 747 on his own and pulled up, banking sharply. He lifted off, avoiding catastrophe by a mere three seconds and 75 feet.

Controllers need AMASS most in bad weather, but the system mistakes rain showers for airplanes. At John F. Kennedy International Airport in New York City, controllers disabled the system one night in July 2005 because of downpours. An Israel Air 767 missed a turn and taxied in front of a departing DC-8 freighter. The freighter pilot later guessed his airplane’s tail came within 45 feet of the 767.

Investigators concluded the system works backward. Making pilots depend on controllers for warnings is like driving a car while waiting for a cell phone call that tells you to watch out for a truck you cannot see, the Department of Transportation’s inspector general, Kenneth Mead, told Congress five years ago. “The very slow pace of fielding technology, the failure to move forward expeditiously with promising new technology, is a major part of the problem and, hence, must be focused on as a major part of the solution,” Mead said.

The FAA also backed research by NASA into a concept that is called “synthetic vision”: a virtual view out the cockpit window that shows pilots everything they wish they could see, but can’t. It’s computer-generated and projected onto a glass screen in front of the windshield. The screen is called a “head-up display” because pilots look straight ahead to view it. Even when thick fog or darkness obscures the view outside, the bright outlines of runways and—with the most advanced technology—the locations of other airplanes appear.

NASA demonstrated synthetic vision aboard a Boeing 757, along with a separate cockpit screen that showed the airplane’s location against a moving map of the airport. Electronic links with the control tower relayed the airplane’s taxi route and the location of other airplanes, so they showed up on the map too. Test flights at Dallas/Fort Worth International Airport in 2000, using a van to simulate another airplane intruding on the runway, found the onboard system alerted pilots to problems 10 to 20 seconds before controllers were aware.

In NASA simulations, the same airline pilots who made wrong turns and other mistakes taxiing through the Chicago airport in low visibility made no errors when they had the displays in their cockpit.

Current head-up display systems, however, do not carry enough airport details to guide pilots beyond the runway. Rockwell Collins began searching about five years ago for airline backing to develop its Surface Guidance System at a likely cost of several million dollars—the final cost will depend on what sort of aircraft the system is being developed for and what other avionics are already on board.

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