A few minutes after midnight, radio recordings show, the TRACON controller handling the flight from Miami made a routine verbal handoff, telling the pilot to contact the National tower.
Unable to reach anyone at there, the pilot aborted the approach, circled the airport and radioed the Potomac TRACON controller for help in aligning the plane for landing. A few minutes later, when the United plane approached for landing, the TRACON controller told him that the tower was not staffed.
The TRACON controller had a similar conversation with a second American plane.
“So you’re aware,” the controller said, “the tower is apparently not manned. We’ve made a few phone calls. Two airplanes went in the past 10 to 15 minutes, so you can expect to go into an uncontrolled airport.”
“Is there a reason it’s not manned?” the American pilot asked.
“Well, I’m going to take a guess,” the controller replied, “and say that the controller got locked out. I’ve heard of it happening before.”
“That’s the first time I’ve heard of it,” the pilot said.
“Fortunately, it’s not very often,” the controller said. “It happened about a year ago. I’m not sure that’s what happened now, but there’s nobody in the tower.”
Finding their way
The first two planes landed and used information from their airlines to find the correct gates. By the time the third plane touched down, after about half an hour of silence, communication from the tower had been restored.
The greatest risk posed by silence from the tower was on the ground rather than in the air. Planes routinely land in smaller airports without guidance from a tower.
In a circumstance like the one that occurred at National, pilots get on the control tower radio frequency and relay their position, speed and distance to other pilots as they approach and land.
“So, other airplanes would know, ‘Okay, he’s clear of the runway, so I’m good to go,’ ” said the source familiar with tower operations.
On the ground, however, the slow nighttime hours are when maintenance crews crisscross the runway — sometimes towing planes — as they prepare for the next morning.
“There are people in the control tower for a reason,” the source said. “There’s a whole lot of activity going on during the night.”
Those maintenance workers contact the tower on a special frequency to get clearance before crossing a runway. Inbound pilots contact the tower on a different frequency.
At airports where the tower shuts down for the night, ground crews and incoming pilots are required to use the same radio frequency to coordinate their actions.
Air traffic controllers who direct more than 1.5 million flights annually in the Washington region made a record number of mistakes last year. Dozens of the errors triggered cockpit collision warning systems.
Nationwide, errors by air traffic controllers increased by 51 percent last year. The record number of errors — locally and nationally — reflects a majority of cases in which planes came too close and some in which a potentially fatal outcome was narrowly averted.
In January, an American Airlines plane carrying 259 people almost collided with a pair of 200-ton military cargo jets after departing New York’s John F. Kennedy International Airport. Official records show that a distracted controller did not respond to a warning from a colleague that the planes were on a converging course.