When there's snow or fog at Logan International Airport and visibility is bad, air traffic controllers rely on ground radar to show them what's happening on the runways.
But there's a problem.
The ground radar system, known as ASDE-X, isn't working the way it should, according to Matt McCluskey, president of the Boston chapter of the National Air Traffic Controllers Association, because it is telling controllers that vehicles like snow plows are on runways when they aren’t really there.
Those phantom images, or false targets, have occurred hundreds of times, McCluskey said, since the ground radar system was upgraded last summer.
“You've cleared an aircraft for takeoff on a runway. The aircraft is rolling down the runway and all of a sudden a false target appears right in front of you,” McCluskey said. “Your heart's about the size of a football at that point. You're sitting there. You're looking up. You don't know what it is.”
Video obtained by Fox Undercover from the Federal Aviation Administration shows just what those false targets look like. On a snowy Saturday afternoon last month, a United Airlines jet was taking off when suddenly a vehicle appeared on the runway in the path of the departing jet.
In the control room that afternoon, air traffic controllers feared the worst.
“It's too late. The aircraft's already up to speeds of approximately 150 miles per hour rolling down the runway. And the false targets are right there. Right in front of the aircraft,” McCluskey said. “You don't know if it's something that went out onto the runway. If it's something or not. Until after the aircraft comes out the other side.”
But then, the jet passes right through it, and takes off safely. It turned out the vehicle was a false target.
Those false alerts, McCluskey says, threaten the safety of the flying public.
“If there's an aircraft rolling down a runway and a controller sees a false target and you can't see anything -- the weather's bad, the visibility's down. If you shut that aircraft down, what's going to happen then? The possibility in a snowstorm, ice, snow on the runway, could the aircraft go off the runway? I'm not sure. I think it could.”
But the FAA maintains the false alerts pose no problems.
“False targets… are a clear part of a radar system,” said FAA official Joseph Davies. “It comes with the territory.”
“This system is operating exactly how it should be,” Davies said.
Davies said the false alerts are a price to pay to make sure the radar sees all true targets.
“We set the system so that false alarms will occur because it focuses the controllers attention to an area that could be of concern,” he said. “We have to be certain that we're always going to depict real targets. And to do so, we may have to pay the price of occasional false targets.”
Davies said the public should “absolutely not” be concerned about the false targets.
“The flying public should continue to enjoy the remarkable safety that exists at Logan airport,” he said.
But McCluskey disagrees.
“It could be a matter of time before a catastrophe does happen,” he said.
It’s potentially a nationwide problem, because the same ground radar system in use at Logan airport, is also at other airports around the country, and will be at 35 airports in all by the end of the year.