The United States has roughly 6% fewer air traffic controllers than it did a decade ago, even as the number of flights relying on the air traffic control system has grown 10%, according to a January analysis from the U.S. Government Accountability Office. That widening gap between staffing and traffic is the arithmetic behind the flight delays travelers encounter when facilities run short-staffed. And the shortage is not confined to American airspace.

Countries from Australia to Qatar now compete for the same limited pool of certified controllers, recruiting across borders with work visas and pay pegged to experience. Aviation training company CAE projects that 71,000 new controllers will be needed worldwide by 2034 — roughly 7,000 per year.

The U.S. cannot join that bidding war. Every FAA controller must be an American citizen, leaving the agency dependent on a domestic pipeline that turns away the vast majority of applicants.

For airlines, that pipeline sets the pace of the whole system. Delta CEO Ed Bastian told Fortune in April that the biggest opportunity for AI in aviation lies in air traffic control rather than inside the aircraft, because it would “do more in terms of helping our customers have quicker travel, more efficient travel.”

Why controllers are so hard to keep

The GAO traces much of the decline to interruptions in training. Government shutdowns in 2013 and in 2018 and 2019 froze hiring and instruction, and the COVID-19 pandemic stopped training entirely for four months before running it at reduced capacity for nearly two years. Elevated attrition from 2019 through 2024 made the recovery harder. Because certifying a controller takes years, the effects of those interruptions lingered well beyond the disruptions themselves.

The 2025 shutdown deepened the shortfall: by November of that year, the FAA said nearly half of major air traffic control facilities were short-staffed as controllers worked without pay.

The nature of the work may be the deeper problem. “It’s one of the highest stress occupations out there,” says Tiffany Bisbey, an assistant professor of industrial/organizational psychology at George Washington University. When controllers appear in academic research, she notes, it is typically as the subjects of studies on stress.

The federal government says as much. The Bureau of Labor Statistics describes the work environment this way: “Their work can be stressful because maximum concentration is required at all times. Night, weekend, and rotating shifts are common.”

The pay isn’t the problem

Compensation is not what keeps candidates away. The median American air traffic controller earned $148,080 a year — $71.19 an hour — as of May 2025, according to the BLS, and the top 10% earned more than $215,610.

The bar to entry is also lower than many people assume. The FAA requires a bachelor’s degree, one year of progressively responsible work experience, or a combination of the two; new hires then spend more than a year training on the job. When the agency pitched the role to Gen Z video gamers this spring, it advertised pay of at least $155,000 after three years.

A global scramble for controllers

Other countries face shortfalls of their own, and some are filling them by hiring controllers trained elsewhere. In September, Airservices Australia posted a call for experienced international controllers, offering a work visa with eligibility to transition to permanent residency and promising “the perfect balance between work and leisure.” Recruiting controllers who are already certified sidesteps the multi-year training process, which is why such postings target experience rather than new entrants.

Australia needs the help. That same month, unplanned absences left eight of Sydney Airport’s 49 controllers unavailable, delaying roughly a third of inbound flights one morning.

The competition cuts both ways. Qatar has been recruiting Airservices Australia controllers, Canada’s NAV CANADA used an outside firm to recruit eight foreign controllers, and South Africa lost 28 controllers in eight months, Reuters reported this month. A spokesperson for the industry group CANSO told the news service that the country that trains a controller usually bears the full cost of that training, even if the controller later leaves.

Why the U.S. can’t hire its way out quickly

The FAA’s qualification rules narrow the pool long before training begins. Applicants must be U.S. citizens under 31 and pass pre-employment tests, a medical exam, and a security investigation. “Less than 10% of all applicants meet these requirements and are accepted into the training program,” the FAA says.

Fewer still make it through: about 2% of applicants qualify for and complete the full training process, the GAO found.

Even so, the agency is hiring faster than it has in years. The FAA brought on 2,235 controller trainees in fiscal 2026, the most in its history, and its 2026-2028 workforce plan puts the certified workforce at about 11,000 as of April, against a target of 12,563. That gap of more than 1,500 certified controllers is the number to track as the record trainee classes move through a pipeline that still takes years to produce a fully certified controller.

That target is new. In May, the FAA lowered its staffing goal by about 2,000 controllers, citing forecast demand and changes to scheduling and training. The National Air Traffic Controllers Association said it was not involved in drafting the plan.

Bisbey sees no safe shortcut. Fast-tracking applicants or compressing training is not a viable fix, she says, and she suspects those who designed controller training “probably thought they needed to do even more, not less.” As she puts it: “It’s such a high-risk organization, and the training is so arduous for a reason.”

The FAA has experimented at the margins, including a 2024 pilot program that let graduates of two Oklahoma schools skip additional FAA Academy training and move straight into facility training. But certifying a controller still takes years, and until the pipeline catches up, travelers should expect more delays.

Bisbey expects most passengers to take those delays in stride, since few would trade a delay for a less safe flight. “As annoying as it is, it’s not going to make people stop traveling.”

This story was originally featured on Fortune.com.