The air traffic control tower at Chicago’s Midway Airport remained shuttered on Monday due to the coronavirus.

It marks the sixth day of the shutdown for the tower after the Federal Administration Aviation abruptly shut it down on Tuesday, March 17, when employees in the tower tested positive for coronavirus.

After the shutdown, the FAA shifted Midway control tower operations to two remote locations outside of Chicago — in Aurora and Elgin, Illinois — where the aviation administration has other regional air traffic control facilities. But that shift necessitated a slowdown in the number of takeoffs and arrivals per hour that Midway can typically handle.

An FAA spokeswoman on Monday confirmed that the Midway tower remained closed. She declined to say when it might reopen.

An FAA website that monitors air traffic control tower operations nationwide said the Midway tower was in the third of three phases of cleaning that are required before the tower can reopen. Additionally, the FAA said on the site it was engaged in self-quarantine of affected employees and ongoing evaluation.

In a further statement, the FAA said “our agency’s mission is to operate the world’s largest and most-complex airspace system. But we have an equal obligation to ensure the health and safety of our employees.”

The FAA also noted in a statement that any disruption can impact the air traffic system and said "we are experiencing this at the handful of facilities already affected by Covid-19."

The air traffic control tower at Las Vegas' McCarren International Airport also remained shuttered as of Monday afternoon after at least one employee in that tower tested positive for coronavirus last week.

A Southwest Airlines (NYSE: LUV) spokesperson did not immediately respond Monday when asked how much the ongoing shutdown of the Midway Airport air traffic control tower continued to impact the carrier’s operations on Monday. Southwest operates more than 90 percent of all flights arriving and departing from Midway.