Danger: Airplane Crossing
Controlling airplanes on the ground is a thornier problem than controlling them in the air.
- By Michael Milstein
- Air & Space magazine, August 2007
(Page 3 of 6)
In one incident, the pilot of a departing commuter jet can be heard on air traffic control tapes gasping for breath after a British Gulfstream jet crossed in front of him, forcing him to jam on the brakes, even though controllers twice told the Gulfstream not to proceed. The commuter’s brakes took 40 minutes to cool down.
The risk of collisions rises roughly twice as fast as the growth in air traffic, according to Arnold Barnett, a professor at the Massachusetts Institute of Technology’s Sloan School of Management. That’s because as more airplanes travel through airports, risk rises in two ways. First, more aircraft are likely to stray into the wrong place. Second, more airplanes make it more likely a straying aircraft will collide with another one. The top 32 busiest U.S. airports already log about twice as many close calls as others.
Based on FAA projections of increases in air traffic, Barnett calculates that, if nothing is done, by the early 2020s, U.S. airports could experience about 15 fatal accidents, killing as many as 700 to 800 people. The low number of major accidents so far indicates that for airplanes to hit each other, errors must happen at precisely the wrong time—and that’s rare. “Not only do people have to make mistakes, but you also have to have really bad luck for a collision to occur,” Barnett says.
Catastrophes have already struck. On a foggy runway on Tenerife, one of the Canary Islands, in 1977, the pilot of a KLM Boeing 747 apparently misunderstood air traffic control instructions and accelerated into a Pan Am 747 taxiing along the airport’s single runway. Everyone on the KLM jumbo and most on the Pan Am airplane died—583 in all.
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.