Duffy says air travel may take 'days if not a week' to return to normal, even after shutdown ends

"If the government opens tomorrow - which it won't, it doesn't look like - it's going to take us days to assess the controllers coming back into their facilities or their towers," Duffy told "America Reports."

"And then once we start to move those numbers back down to zero on our required 10%, the problem is the airlines then have to put those planes back on for booking again," he said.

Duffy said there will be a lag of several days to a week before airlines and airports can return to normal operations.

"It's going to take some time for the airlines to respond. So once we see more controllers in the towers, then the airlines have to respond to that," Duffy said. "It can be days, if not a week, before we get back to full-force flights when the shutdown ends."

However, if the federal shutdown continues, the cuts will multiply due to an increase in the air traffic controller shortage.

"With that, you might see 10 percent would have been a good number, because we might go to 15 percent or 20 percent," Duffy said.

While he told the outlet the figure was "theoretical," he noted it remains a possibility.

"Could it go there? That's possible. There's no plan for that," Duffy said. "I assess the data and how many controllers I have, and I'm just saying we're going to make decisions based on what we see in the airspace to make sure we keep it safe. I hope it goes the other direction."

The announcement comes as the government shutdown rolls into its 38th day.