From NPR.

Transportation Secretary Sean Duffy says he could be forced to close some of the nation’s airspace if the government shutdown continues into next week: "You will see mass flight delays, you’ll see mass cancellations, and you may see us close certain parts of the airspace, because we just cannot manage it."

Duffy says it is safe to fly, but that the FAA will restrict the number of planes in the air if there aren’t enough air traffic controllers to manage the system safely. Air traffic controllers are required to work without pay during the government shutdown, which hurts morale and has lead many to call in sick, creating staffing shortages and extensive delays at airports across the country.