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
Runway 35 Left at Denver International Airport looked clear to the pilots of a Frontier Airlines Airbus A319 as they dropped from a 600-foot ceiling of clouds one morning in early January 2007. Blowing snow cut visibility to about a half-mile, so they were flying an instrument approach.
Then they saw the airplane sitting on the runway, dead ahead. The pilot of the Key Lime Air cargo turboprop had inadvertently followed blue taxiway lights (the centerline lights were obscured by the snow), turning onto a 12,000-foot active runway at the nation’s sixth busiest airport. A puzzled ground controller asked him where he was, just as the Frontier pilots spotted his airplane and yanked the nose of the Airbus up to abort the landing.
A collision alarm sounded in the tower. The two airplanes missed each other by about 50 feet.
Nearly once a day, on average, an airplane or airport vehicle ends up on a U.S. airport runway where it is not supposed to be. Such potentially hazardous incidents are called “runway incursions.” Not all are as dangerous as the close call in Denver—one of at least five instances there since 2000. But according to the Federal Aviation Administration, almost every 10 days an incursion poses the serious chance of a collision. Only last-second reactions by pilots have averted several disasters.
The good news is that there are ways to prevent incursions. More than a decade of research by NASA, the Department of Transportation, and aviation companies shows that cockpit displays, like the moving maps now widely available in automobiles, plus bolder runway striping and lighting at airports, can prevent the most common pilot errors that cause incursions. Basic improvements are now becoming available. But growth in air traffic is making incursion rates rise (incursions more than doubled nationally as air traffic grew between 1994 and 2000), so safety leaders want to pick up the pace.
“We’ve got the technologies; it’s now a question of deciding which of those technologies to use,” says Mark Rosenker, chairman of the National Transportation Safety Board, which began pressing the FAA in the 1970s to step up prevention of runway incursions. “Too many incursions are occurring annually,” Rosenker says. “We’ve been running on luck, and luck is no way to run a national air system.”
The reality is that, until recently, runway incursions were eclipsed by more serious dangers, such as airplanes colliding in the air or flying off course and into the ground (known as “controlled flight into terrain”), says Basil Barimo, vice president of operations and safety for the Air Transport Association, which represents the airline industry. Now that cockpit warning systems have greatly reduced those risks, runway incursions have risen to the top of the safety to-do list.
“You get the biggest risk first and then you work your way down,” Barimo says. “While runway safety is getting a lot of attention now, it’s only because we’ve eliminated, quite frankly, the more significant risks.”
There is no simple solution for runway incursions because there is no single cause. According to federal statistics, more than half happen when pilots make a wrong turn or fail to stop short of a runway; responsibility for the rest is split between air traffic control mistakes and airport workers going astray when towing airplanes or driving trucks.
“It’s sort of hard to crack the code of why this happens,” says former FAA Administrator Jane Garvey, who made runway safety a priority during her term, from 1998 to 2002. “You find an awful lot of human error. Those are always more difficult because they are unique to the individual.”
Pilots sometimes refer to travel between the runway and an airplane’s parking spot as “the forgotten phase of flight”—and many consider it the most demanding. Sweeping tarmac disappears into the horizon, especially at night, when airfields become a sea of blue taxiway lights. Sophisticated instruments that help pilots navigate in the air offer scant help on the ground, leaving air crews to find their way with little more than paper maps. Pilots must combine what they see out the window with their map of the airport to figure out where they are, at the same time they’re communicating with their airline and ground control and maneuvering the airplane. “There are points when [successful communication] doesn’t happen, and that’s how we end up with incursions,” says Rick Shay, a United Airlines pilot. Experts call the lapses “loss of situational awareness.”
While high-end automobiles now carry color electronic maps that display the car’s location on roads and highways, “we don’t have that in our cockpits,” says Terry McVenes, a US Airways captain who leads safety efforts for the Air Line Pilots Association.
David Foyle, who studies incursions at NASA’s Ames Research Center in California, recalls sitting with two pilots in the cockpit of a NASA Boeing 757 at a three-way intersection at Atlanta’s Hartsfield-Jackson International Airport a few years ago. The pilots couldn’t agree on which way to go. “They stopped the airplane and they started arguing about it,” Foyle says. The airplane was already past signs for the intersection, and the pilots had no way to tell on their own where they were. It turned out neither pilot was right.
It doesn’t help that many busy airports were not designed for today’s booming air traffic, says Paul Erway, the FAA’s acting director of runway safety. As incursions multiplied, the FAA increased training for controllers and launched campaigns to educate pilots. That has helped, says Erway. What’s left are a stubborn few errors that may never be eliminated as long as people are involved.
“Because we’re human, we’re going to make mistakes,” he says. “What we’re looking at now is modifying the system so the inevitable human error doesn’t result in catastrophe.”
Los Angeles International Airport has recorded more than 40 runway incursions since 2001. The cramped airport layout, dating to the 1950s, forces airplanes to cross two inner runways and two parallel outer runways to go between terminals. Aircraft cut across the inner runways roughly 900 times a day. Twice last year, controllers told pilots to stop before crossing and heard the pilots repeat the instructions back, only to see the pilots go across the runway anyway—into the paths of airplanes that were taking off. Almost every day, says Michael Foote, an air traffic controller at LAX, at least one pilot does not follow his instructions.
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.
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.
The goal was to translate NASA’s demonstrations into commercial reality. The vision was grand: Pilots would see taxi routes projected onto the screen in front of them, advising them how to adjust their speed to make the next turn. Traffic cones would pop up across their paths when they approached a runway they should not cross. But then came September 11, 2001, and suddenly airlines were more focused on survival than investment.
“Everybody thought it was a great idea, but there was no money to develop it,” says Peter Howells, the main system engineer at Rockwell Collins. The other problem, he adds, is that while everyone is concerned about incursions, many airlines see it as a problem caused by the mistakes of other pilots. “They say, ‘It’s not us that has the problem. It’s those other people. Why should we invest in this equipment when it’s the others causing the issue and we’re essentially the victims?’ ”
NASA’s Foyle and Becky Hooey, a San Jose State University researcher based at the Ames center, found a good reason for such investment when they studied the performance of pilots in NASA simulators. Advanced displays reduced pilots’ workload; a moving map helped plot their route, and a head-up display helped them plan upcoming turns. They taxied faster and reached the gate sooner. Rockwell calculates the extra speed would enable a 737 carrying about 150 people to earn another $35,000 to $50,000 a year. That payback will probably drive what airlines will spend on the system, Howells says. But FAA leaders and others caution that an elaborate new system does little good if airlines cannot afford to install it in their airplanes. While new-generation aircraft will likely carry head-up displays as standard equipment, it’s difficult for airlines to make a good business case for installing the displays purely in the interest of runway safety, says Barimo of the Air Transport Association.
As a backbone of its strategy to handle traffic in ever-busier skies, the FAA is now investing heavily in ADS-B, a system that provides more precise air traffic data (see “How Things Work: Aircraft Identification,” Oct./Nov. 2006). The system will help prevent runway incursions too, making it easier for controllers and pilots to see the location of aircraft on runway maps. But it will cost close to $7 billion—with the price split among the FAA, airlines, and others—and will not be completely finished until 2035.
“This is a very important area to us,” FAA spokesperson Laura Brown says. “But we have a lot of other technologies we’re working on, and they always compete for funding.”
There is also a resistance to filling cockpits with gadgets, both because of cost and because no one wants to distract pilots, says Robert Francis, a longtime FAA official who later served on the NTSB. And any new equipment for airplanes must be foolproof before it can be put in place.
“The real challenge is: How do you balance the need to be responsive with the need to be so careful and so precise?” says former FAA administrator Garvey. “The degree of precision in navigating a car is very different than what you have to have in aviation.”
Controllers are getting an important new tool as well: a new ground radar system known as Airport Surface Detection Equipment, Model X. It provides an all-weather view of the airport by combining radar signals with data from airplane transponders. An electronic airport map labels each aircraft on the screen so controllers know which is which. But it, too, is behind schedule, because of funding problems, and will not be in place at 35 leading airports until 2011.
One bright winter day, Markus Johnson, chief test pilot for Honeywell Aerospace, lines up his Beechcraft King Air for takeoff from Salem, Oregon. The sun glares in his eyes, but he’s on the right heading to depart from Runway 16. He guns the engines and the airplane rolls faster. Suddenly, on his headset, he hears an urgent voice: “On taxiway! On taxiway!”
His airplane carries Honeywell’s Runway Awareness and Advisory System, an inexpensive (less than $20,000) software upgrade to a common system that warns pilots when they approach dangerous terrain. It contains electronic airport maps and closely monitors the airplane’s direction and speed. Six airlines have already installed it.
“There are a million different reasons why pilots lose track of their position,” Johnson says. “What we want is RAAS to be this third guy in the cockpit who’s just watching and is going to tap you on the shoulder and say, ‘Here’s where you are.’ If you agree with that, that’s great. If you don’t agree with that, you say, ‘Let’s stop and see what’s wrong.’ ”
For pilots of a Comair commuter jet that took off from the wrong runway in Lexington, Kentucky, last August, the runway awareness system would have given three key warnings they were off course: when they approached, when they lined up, and again when the system recognized the runway was too short for their jet to take off from. As it was, the pilots didn’t realize that until they were beyond the point where they could abort their takeoff; 49 of 50 people aboard were killed.
At San Diego’s Lindbergh Field, the busiest single-runway commercial airport in the nation, the runway is sacrosanct. “Our dependency on the use of that runway is absolute,” says Ted Sexton, vice president at the airport and a former Navy pilot. Airplanes scream in and out less than two minutes apart on average, so if anyone happens to stray onto the runway, “someone gets hit in two minutes.”
Now San Diego has a new tool to keep pilots on track: prototype FAA warning lights that signal pilots to stay off the runway when it’s occupied. Consider it a $6 million stoplight. They’re called runway status lights, and they’re embedded in the pavement at key runway intersections. When airport radar detects an incoming airplane within a mile of the airport or a departing airplane accelerating above 34 mph, the red lights switch on. It’s a clear no-go signal to waiting pilots.
There’s a delicate balance at an airport this busy: It can’t afford lights that slow traffic like an ill-timed stoplight on a busy highway. These lights switch off just before it’s safe to cross, because waiting airplanes will take a few seconds to spool up their engines before they actually begin moving onto the runway. By that time, the runway will be clear.
Similar “stop bars” of red lights built into the intersections at major European airports, such as London’s Heathrow, make incursions a non-issue there, the NTSB says. U.S. Department of Transportation studies of past runway incursions suggest that runway lights would have alerted one or both of the pilots in about 65 percent of cases. The lights, combined with the slow but still helpful AMASS system, would catch about 85 percent of all incursions, the studies found. A similar prototype in Dallas won raves from pilots. A single Dallas runway may handle 450 flights per day, with 500 runway crossings mixed in. More than 90 percent of pilots surveyed said the lights would reduce incursions. The FAA now considers the lights very promising, and will decide later this year whether to expand the program to other airports.
Last March, FAA Administrator Marion Blakey eliminated an FAA requirement that electronic cockpit maps work in the air as well as on the ground. They can now be developed for ground-only use. That will “change how pilots safely navigate runways, the way GPS changed the way we drive our cars,” she said. “I’ll say it plainly: It needs to be in the cockpit. It’s ready, we’re ready, and aviation needs it.”