Invisible Highways: An Inside Look at Air Traffic Control in the U.S.

Note: This was originally published on the Aviation Queen blog, where I have been fortunate enough to post as a guest contributor thanks to the immense kindness of Benét Wilson.

While I love music, these days I find myself listening to air traffic control feeds more often than tunes. On average, more than 400,000 landings and takeoffs occur at Minneapolis-St. Paul International Airport each year, and the fact that the controllers get them all on and off the ground safely never ceases to amaze me.

So when passengers at Amsterdam’s Schiphol Airport were faced with serious flight delays in early February due to a computer issue in air traffic control, it really got me thinking about our own ATC system.

How exactly does it work? Is there a “backup” plan in the event something similar happened here?

According to a video released by the FAA, controllers have two primary jobs: to make sure planes are properly separated from one another, and to keep air traffic flowing in the most efficient manner.

When planes depart, an initial heading is used and then they fan out into their specific routes. When planes are nearing their destinations, they’re sequenced and merged into “arrival streams.” And in the air, planes have both a minimum lateral and vertical distance they must remain from one another.

Near airports, planes flying at the same altitude must be at least three miles apart, but at higher altitudes that jumps to five miles. And if planes don’t meet those lateral requirements, they must remain a minimum vertical distance from other one another. For commercial aircraft below 41,000 feet, the minimum vertical separation is only 1,000 feet. So when you’re at cruising altitude, the distance between your plane and one that’s above or beneath you could be as small as the length of three football fields.

Departures and arrivals also have numerous crossing routes where they must be separated from one another, so controllers are continually managing and separating them throughout the day.

So how exactly do air traffic controllers do their job?

Derek Sorenson has worked at the Minneapolis Air Route Traffic Control Center (ARTCC) for roughly three years, first as a contractor and more recently as a controller. The Minneapolis Center is one of 21 ARTCC facilities in the U.S. and encompasses nearly 400,000 square miles of Midwest airspace.

Sorenson is responsible for an area that covers roughly the northern half of Wisconsin, the upper peninsula of Michigan, and the northern half of the lower peninsula of Michigan. And a lot of planes fly through that airspace on any given day.

“If it were averaged throughout the year, I would estimate something like 2,000 aircraft per day,” he said.

Before departing, pilots file a flight plan with the ARTCC, which includes their requested route and altitude. The controllers do their best to accommodate these requests, but that’s not always feasible. “Sometimes, for traffic situations or a required route to be flown to a busier airport, we need to change things up,” Sorenson said.

There’s no such thing as a “typical day” for Sorenson, and he likes that. “It all depends on many factors such as traffic volume, weather, turbulence, and how many people are working that particular shift,” he said.

On the job, he is in constant communication with pilots via radio, and with other controllers via phone. And when it comes to tracking aircraft, he primarily works off of a radar display that runs on En Route Automation Modernization (ERAM). ERAM technology is a vital component of the Next Generation Air Transportation System, commonly referred to as NextGen, and is helping in the transition from an aging ground-based air traffic control system to a more modern satellite-based system. Previously, controllers could only track 1,100 aircraft at a time, but the use of ERAM has increased that capability to 1,900.

Lucky for him, Sorenson has never encountered a significant system failure akin to what happened in Amsterdam, and he isn’t aware of any past incidents at the Minneapolis ARTCC. The most notable event he could recall here in the U.S. was in September 2014 when a contract worker set fire to the Chicago Center early one morning. As a result, thousands of flights into and out of both Chicago O’Hare and Midway airports were delayed or canceled.

“In the Chicago incident, they lost communication and radar… so they were ATC-Zero,” said Jennah Perry, Program Chair and Assistant Professor of Air Traffic Management at Embry-Riddle Aeronautical University.

The Independent reports that in Amsterdam, the fault apparently occurred with radar correlation software, which compares and assesses information from primary and secondary radar. Perry explained that primary radar detects anything that has mass, whereas secondary radar only picks up aircraft that are carrying a transponder.

“I would imagine it is the system that puts them together that failed,” Perry added.

According to Perry, the FAA is supposed to have contingency plans in the event of radar failure. In the Chicago situation, even though there were plans in place, they didn’t work. The controllers didn’t have proper training on following the plans and there wasn’t proper infrastructure.

“Due to the high demand of air traffic and the lack of ability to train and be current on those non-radar procedures, those contingency plans are ineffective in the event they have to be used,” Perry said.

The contingency plans in place in Chicago were designed for short-term use, which created limitations and required controllers to discard the plans and instead work with adjacent centers such as Cleveland, Minneapolis, Kansas City, and Indianapolis.

A similar incident happened in October 2015, when record rainfall caused flooding at the Austin-Bergstrom Terminal Radar Approach Control (TRACON), also resulting in an ATC-Zero situation. The damage affected the operations for more than two weeks.

Over the last three years, a number of incidents have revealed a lack of resiliency in the current air traffic control structure, but ultimately, it was the fire at the Chicago Center that led to the FAA’s extensive review of its current contingency plans.

According to a January 2017 report released by the Office of the Inspector General, the FAA’s contingency plans are not yet sufficient to minimize the impact of system disruptions.

Following the Chicago incident, the FAA updated its contingency plan policy to include goals to achieve 90 percent capacity at the top 30 airports with the most passenger activity within 24 hours, and 90 percent capacity at facilities that manage air traffic at high altitude and in the vicinity of airports within 96 hours. But in a crisis situation, that’s just not realistic given the current plans, according to Perry. “The centers will not be operating at normal capacity… they’ll be operating at maybe 30 to 40 percent,” she said.

Additionally, the Air Traffic Organization (ATO) completed a 30-day assessment of the operational contingency plans, which identified five next steps that needed to be completed within one year. However, two of those steps have not yet been fully completed.

“Right now if any major facility went down in the U.S. to ATC-Zero, it would cause major havoc over the whole U.S. airspace system,” Perry said. “It’s a domino effect.”

According to her, our current radar-based system just won’t cut it… the only thing that can bring our centers up to the 90- to 100-percent efficient status they’d need to be at following a crisis is NextGen.

Key site testing for NextGen’s NAS Voice System (NVS) is expected to be complete in 2019. This voice switch capability would allow controllers to talk to any aircraft anywhere in our airspace. So if one facility lost communications, another facility could communicate with their aircraft. Once these systems are certified and available, they’ll be installed in terminal and ARTCC facilities, likely between 2019 and 2026.

Perry said the change in technology is great, theoretically, but it’s timely and expensive.

“It has a lot of advancements that we need in order to keep our system safe and streamlined, but with technology comes failure… redundancy needs to be there.”

So while flying is statistically the safest form of travel, more work needs to be done to keep it that way. The FAA has made progress by establishing goals and working to achieve them, but the January report concluded that until the administration strengthens controller training and implements policies and procedures for transferring traffic within all airspace, they’ll continue to face challenges.

Realistically, in a situation similar to what happened in Amsterdam, we probably wouldn’t fare much better than they did. But in the next 5-10 years, once NextGen is fully implemented, a center’s response to a crisis will almost certainly be much smoother and more effective, making our skies even safer than they are today.