Most of the nation's air traffic controllers — the folks who, among other things, prevent commercial flights from crashing into each other — are among the roughly 800,000 federal workers who will not be receiving a paycheck Friday.

That's because of the partial federal government shutdown, now in its 21st day, with no end in sight.

About 10,000 air traffic controllers who work for the Federal Aviation Administration, 51,000 Transportation Security Administration officers and an undisclosed number of federal air marshals have been told to keep reporting to work because they're deemed essential.

This includes Frederick Naujoks and his fellow air traffic controllers at San Francisco International Airport. Naujoks, local president of the National Air Traffic Controllers Association, and his colleagues have been reporting for work every day to make sure the airport's roughly 2,000 combined daily departures and arrivals take off and land safely.

Government employees have always been paid after past shutdowns, and that's the expectation this time, too. But that assurance doesn't help pay the bills right now.

KQED's Brian Watt spoke with Naujoks about the situation, and whether air travelers should be worried about potential safety impacts due to the shutdown. Here is an abridged version of their conversation.

So you guys are still showing up to work, right?

Absolutely. We are still working, those of us that are certified on at least one position. There's about five positions in the tower. We're still going to work every day, but we're not getting our paychecks. The primary impact is that people are going to work without pay. They're going to work for an IOU.

The secondary impacts are a lot of training is being suspended or stopping. We don't have the manpower to provide classroom training. We don't have the simulators available to us to provide training that's not on-the-job training and the staff support specialists that help us out with a lot of the backend duties. They're furloughed and they're not coming to work.

So people are manning the towers and the centers and they're guiding the flights from point A to point B — but that's just the first layer. All those secondary layers are gone.

Is it safe to fly?

I wouldn't say that it's a safety issue at this moment. We are still going to work. We are still treating every flight as if our family members are on those flights.

The problem is that safety is something that you build up on. We call it a Swiss cheese model. We layer Swiss cheese until you can't see the holes through it, and hopefully if something passes through one layer it won't get all the way to the bottom.

What we're starting to do is, we're peeling off layers by lengthening the shutdown. Because without getting training done, without getting quality assurance and looking at event analysis done without any of these pieces that are from the back end of our job getting accomplished, eventually you're eroding away what is essentially a very safe and robust system.

We don't want to throw that away at all. We wanted to keep it safe and robust, but we can't do that.

So what does this mean for the men and women who do this work in the tower?

I don't want to complain too much because we are very well paid. But when you talk about Bay Area living standards and the cost of living around here, it does end up being a paycheck-to-paycheck job for many people.

I mean, sure, you're putting some money away in the midst of that, but we are primarily counting on that next paycheck to make our mortgage payments, to make our rent payments, to pay our insurance, to pay for our kid's school.

All of that stuff is not there.

We've got some promise from our credit union that they will offer us some short-term, low-interest loans. But, you know, how long can we really live off of that?

It's the promise of the IOU and not knowing when that next paycheck is coming is a little bit scary because we just don't know how much we need to cut back on our purse strings.

I've even had a couple of people come to me and say that they want to work for Lyft or Uber, in addition to coming to work and working air traffic.

For real?

For real. Yeah, they said that if this lasts more than two paychecks they can't sustain themselves otherwise.

That doesn't strike me as safe either for the roadways or the airways.

I would hate to be as fatigued as you would be if you were working both of those jobs.

And air traffic control has always had some staffing challenges, right?

That's correct. And we are actually at a 30-year low in staffing right now.

Nationwide, we're about 2,000 bodies short from where we need to be. At SFO we're about six bodies short from where we need to be, and that's out of a staff of 30. So that's a pretty big percentage.

So, yeah, we have a lot of staffing challenges. There's a lot of overtime already, and now people are going to work six days a week for no paycheck.