Delta Air Lines CEO Ed Bastian told CNBC that the carrier’s operation is running smoothly despite the federal government shutdown, but if it goes another 10 days that could change.

More than 13,000 U.S. flights were delayed this week, some of them due to shortages of air traffic controllers, raising concerns about strains on the country’s aviation industry during the shutdown.

Transportation Secretary Sean Duffy warned Monday that the Federal Aviation Administration is seeing a “slight uptick” in sick calls of air traffic controllers.

Bastian also said the shutdown is exacerbating concerns about the strain on air traffic controllers, a shortage of whom has vexed airline executives for years. Under the shutdown thousands of federal employees, including air traffic controllers and Transportation Security Administration officers at airports are working without pay.

Delta’s CEO said in an interview that the airline hasn’t seen “any impacts at all” so far from the shutdown but urged a quick resolution. A more than monthlong government shutdown from late 2018 to early 2019 ended hours after an increase in sick calls from air traffic controllers snarled travel in the New York area.

“I would say that if this doesn’t get resolved, say beyond another 10 days or so, you probably will start to see some impacts,” Bastian said in an interview with CNBC’s “Squawk Box” Thursday.

A perpetual shortage of air traffic controllers has vexed U.S. airline executives for years, and the FAA has scrambled to increase hiring.

Delta on Thursday reported better-than-expected third-quarter results and forecast a more profitable end of the year than analysts expected.