Authorities are investigating after an air traffic controller at McCarran International Airport became incapacitated for a period of time earlier this week while her co-controller was on a break.

Federal Aviation Administration officials say there were no safety events, losses of required separation between aircraft or conflicts between the airfield and the aircraft during that period, which happened after 11 p.m. on Nov. 7. But the agency has restricted the controller from working and is investigating the incident, which attracted the attention of Nevada Rep. Dina Titus.

“I’ve been briefed on the incident that occurred at the air traffic control tower at McCarran and am awaiting further details, but I find the initial reports deeply disturbing,” Titus, a member of the House Subcommittee on Aviation, said in a statement on Friday. “The safety of travelers is of paramount concern and I will work with the FAA and McCarran as this investigation continues to unfold.”

FAA officials declined to elaborate on how the controller became incapacitated or answer whether there was a medical episode, intoxication, or sleep issue involved, citing the controller’s privacy. They said the controller’s performance appeared to degrade at 11:09 p.m., about an hour into her shift, before becoming impaired at 11:24 p.m. and unresponsive at 11:47 p.m.

A second controller entered the cab atop the tower where controllers sit at 11:50 p.m. and took over air traffic duties at 11:54 p.m.

FAA officials said pilots contacted controllers at the Las Vegas approach control at the base of the tower, who notified the controller who was on a break about the situation.

The agency said some pilots opted not to take off or communicated directly with other aircraft via radio while the controller was unable to complete the task. Ground aircraft held their position or proceeded with caution while trying to talk with the controller and communicating with each other, according to the FAA.

“The FAA is deeply concerned by the incident, is thoroughly investigating what occurred, and is taking immediate steps to modify its overnight shift staffing policies,” the agency said in a statement.

While controllers are allowed to take breaks, the agency said it is implementing a policy effective Friday requiring two controllers to be in the cab until a certain time based on traffic levels and shift periods.

National Air Traffic Controllers Association President Paul Rinaldi said the union will cooperate with the FAA as they investigate.

“It is important to remember the outstanding work that that is done every day by the thousands of men and women who keep the National Airspace System safe. Our air traffic controllers in Las Vegas and around the country do an exceptional job day in and day out and demonstrate the highest professional standards,” Rinaldi said in a statement. “Our top concern is the safety of the National Aviation System. We are proud of our safety record both in Las Vegas and at every facility and will continue to work to keep our airspace system the world’s safest.”