(Adds FAA statement)
CHICAGO, March 17 (Reuters) - The Federal Aviation Administration said on Tuesday it was temporarily closing the air traffic control tower at Chicago Midway International Airport after three technicians tested positive for the coronavirus, prompting contingency plans at the airport and other facilities across the country.
The FAA closed the tower at 5 p.m. CDT (2200 GMT) and it was going to be cleaned again. It was not clear when it would reopen. Arriving and departing pilots will announce their presence and intentions through airport frequencies.
The agency issued a temporary ground stop after it closed the tower, but it was not expected to last for a significant period.
Southwest Airlines Co accounts for the vast majority of traffic at Chicago's Midway.
The FAA said in a statement that "the air traffic system is a resilient system with multiple backups in place. This shift is a regular execution of a longstanding contingency plan to ensure continued operations."
The FAA said previously the Midway Control Tower had been cleaned in accordance with guidance from the U.S. Centers for Disease Control and Prevention.
The diagnoses are in addition to three separate cases that the FAA disclosed to its employees in a letter on Monday, the first positive coronavirus cases among the agency's employees.
One of the employees works at FAA headquarters in Washington, another at an aviation safety district office in Chicago and the third in finance and management in the agency's Eastern Region in a full-time telework capacity, the FAA said. (Reporting by Tracy Rucinski and David Shepardson; Editing by Paul Simao and Peter Cooney)