Intermittent instability reached as many as 17 of 22 control centers
The FAA grounded flights nationwide Friday because of issues at regional air traffic control centers, an FAA notice said. Trump administration officials said Saturday in a press briefing that the nation’s air traffic control system overloaded antiquated equipment and caused “intermittent” communications and radar gaps, leading to the ground stop. The order was lifted late Friday.
Duffy said the contractor work involved replacing a section of the system’s old and discontinued copper wire with new fiber wire in a remote location on Friday afternoon, and he noted that such work has been happening across the country and across industries for decades.
“Specifically, we had over 1,000 connection attempts every 4 to 5 seconds,” Duffy said. “And what that did was gave us issues with our communication with airplanes, and it also caused some disruption with our radar feeds. And when we see that, your safety is paramount, we shut down the airspace.”
Planes flying at the time of the ground stop were able to land safely using “well-known procedures” in place for such circumstances, Duffy said Friday.
The government has been working to overhaul the outdated technology air traffic controllers rely on since Congress approved $12.5 billion for the effort last year. Miles of old copper wires have been replaced with fiber optic lines, while old radio systems are gradually being replaced at airports. The work is far from complete, and Duffy used news conferences on Friday and Saturday to urge Congress to provide more funding.
The United States operates 22 regional air traffic control centers managed by the FAA, which oversee long-distance aircraft operating between departure and arrival airports, according to Michael McCormick, associate professor and program coordinator in the Department of Applied Aviation Sciences at Embry-Riddle Aeronautical University. McCormick estimates these control centers take over flights at altitudes over 10,000 feet.
These centers, which operate in such places as Anchorage, Alaska, Houston and Indianapolis, are one of the three layers that guide pilots. Airport towers direct pilots at takeoffs at the 500-plus airports that have towers. Terminal Radar Approach Control centers then guide pilots as they get further away from the airport, and the regional control centers take over after that. When descending, the reverse happens, experts say. Experts say the controllers at the regional centers sit at radar displays and are responsible for only that airspace.
Stephen Creamer, president of the Air Traffic Control Association, a trade group for equipment manufacturers involved with air traffic control, described the transfer between controllers. “As you fly, your flight is handed off from one controller to another controller,” Creamer said. “That handoff process is like taking the screen and the aircraft on one screen and making sure it’s on someone else’s screen before you send the communications over to that next controller and have the pilot start talking to them.”
McCormick said the country’s regional, high-altitude air traffic control centers need to be connected to remote radio transmitter or receiver sites to allow for radio frequency coverage to communicate with the aircraft. Those transmitter sites are connected to the centers via telecommunications systems that are moving from copper wires to fiber optic lines, and the two-way communication is important to ensure, among other things, that planes maintain safe spacing.
“What is especially problematic in this case is that it’s what’s known as a rolling outage,” McCormick said. “In other words, it’s unpredictable and it may impact one air traffic control center now and then it gets better and then impacts another air traffic control center.”
Bedford told reporters Saturday that intermittent frequency instability affected as many as 17 of the 22 U.S. regional air traffic control centers. “The thing that was unique about this is that it was a type of failure that wasn’t local because it was part of the communication system,” Bedford said. “It propagated around the country.”
In September, Newark Liberty International Airport temporarily lost radar communications with aircraft after a backup fiber optic line was inadvertently cut by railroad construction workers, forcing the FAA to immediately cancel hundreds of flights going in and out of the airport. Airline experts said that scenario was different from what occurred on Friday.
Andrew Charlton, an aviation consultant, said the “knock-on” effect of a nationwide disruption is considerable, because aircraft do not simply fly from one airport to another and stop; they move on to the next destination and the next. Charlton said the effect is exacerbated on long-haul flights and international flights over the Atlantic or the Pacific.
Aviation experts said pilots can still communicate with aircraft even during intermittent communications disruptions, noting that many planes have satellite phone systems. John Hansman, aeronautics professor at MIT whose research includes information technology in aviation, said pilots can still talk directly to other pilots in nearby airplanes via radio, and that equipment on the airplane tells pilots if there are airplanes around them. If a control tower loses radio capabilities, it can also communicate with pilots with high intensity light beams, which send signals to pilots to alert whether it is safe to descend.
“We have a number of backup systems that allow the airplanes to fly safely to the extent that air traffic control can still communicate directly with the radio,” Hansman said.
McCormick and other aviation experts said the FAA is now transitioning to what is known as controller pilot data link — a digital, text-based messaging system that allows controllers and pilots to exchange routine clearances, instructions and requests through the data link instead of voice radio. McCormick said it could take days for airlines to resume normal operations after officials lifted the grounding order.