The circumstances surrounding why an air-traffic controller apparently became incapacitated while working alone in the tower of a Las Vegas airport during a busy night shift earlier this week is under investigation, officials said Friday.
For about 40 minutes a female controller slurred her words while communicating with 29 pilots in the air and on the runways of McCarran International Airport before apparently losing consciousness.
"An air-traffic controller at the Las Vegas tower became incapacitated while on duty," the Federal Aviation Administration said in a statement. "No safety events occurred during this incident."
It did not identify the controller or whether she had experienced a medical emergency.
The woman began her shift at 10 p.m. Wednesday, the Las Vegas Review-Journal reported. She worked for a little more than an hour before trouble began.
Air-traffic recordings available on the internet show commercial airline pilots having difficulty understanding the controller during radio communications about approaches to land, clearances to take off and directions for taxiing. Some begin talking between themselves about something being amiss.
At one point, the controller sounds sleepy and apologizes over the radio, saying she is "choking a little bit." Minutes later, she misstates an aircraft's call numbers. Finally, her microphone opens to the sound of coughing and grunting.
She does not respond to a pilot's inquiry before the sound of a male voice is heard in the room asking if the woman is all right.
A second controller was on duty at the time, but had left for his break, which the FAA allows, the Review-Journal reported. He was called on to return to the tower after the incident began.
The FAA said the woman was put on administrative leave, and the agency ordered two controllers to be in the tower during busy hours.
"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 statement said.
The Associated Press contributed to this story.