The controllers do this by sequencing and coordinating planes in a vast ballet of the sky, so airliners can line up dozens of miles out from the approaches to LaGuardia or SFO or LAX or O’Hare, and then can touch down safely one right after the other, pushing these finite amounts of takeoff-and-landing space toward their theoretical maximum capacity. Controllers do this with the unflappable calm that we’d all like to think we’d exhibit in times of stress—and that controllers virtually always do. I say this based on reading articles about controller training, like this and this, having visited control centers around the country, and dealing with controllers over the decades as a pilot myself, leading to articles like this one (about the sangfroid of the team at LaGuardia, when one plane had a landing problem that closed a runway and the controllers immediately had to reroute the dozens of other planes headed toward the same spot).

Read: Will the government ever reopen?

These men and women are doing America’s work, they’re doing it skillfully and safely, and they’re doing it with constant reminders of the very high stakes if they should screw up.

And right now, they’re doing it without paychecks. For reasons that have absolutely nothing to do with any controller as an individual nor all controllers as a group, they’re all being told to show up, keep millions of passengers as safe as ever, and worry about their back pay some other time.

As the Airline Pilots Association said this past weekend, in a letter urging an end to the shutdown, the controllers and other workers “are dutifully providing safety of life services while facing increasingly difficult financial pressures to provide for those dependent on their paycheck.

“The pressure these civil servants are facing at home should not be ignored.”

Will some airliner crash because of the shutdown? I don’t think so. The system is so triply redundant in its safety awareness and practices that a catastrophic failure, while always possible, remains improbable. But what will happen, and no doubt already has, is that the air-travel system as a whole will further slow down, precisely because people are aware of the additional safety risk.

If you’ve ever traveled in China’s commercial airline system, you know how modern its airplanes are—and how slow its operations are, compared with those in Europe or North America. That’s partly because China has so many people, so few airports, and so little airspace that’s not under military control. But it’s also because the air-traffic control system there has so much less experience on which to draw than North America’s or Europe’s, and therefore builds extra safety buffers into everything it does. (For instance: Planes might land every 60 seconds at the busiest U.S. airports, versus every three or four minutes at a busy Chinese airport.)