The controller at Reno-Tahoe International Airport was out of communication for about 16 minutes when the aircraft carrying at least three people was landing about 2 a.m. Wednesday, the FAA said. No injuries were reported.
"This is absolutely unacceptable," Transportation Secretary Ray LaHood said in a statement. "The American public trusts us to run a safe system. Safety is our No. 1 priority and I am committed to working 24/7 until these problems are corrected."
It was the second case this week of a controller being suspended for sleeping on the job. A controller at Boeing Field-King County International in Seattle fell asleep during his morning shift on Monday and was suspended, FAA said. He was already facing disciplinary action for sleeping on two separate occasions during an early evening shift in January, the agency said.
The National Air Traffic Controllers Association has warned against putting controllers alone on shifts and assigning tiring work schedules.
At most airport towers, there's no bathroom in the cab - the room on the top of the tower. With only one controller on duty, the position has to go unattended at times if the controller needs to use a bathroom. It's common for the nearest bathroom to be located down a flight of stairs from the cab.
Two controllers at the airport in Lubbock, Texas, were suspended for an incident in the early morning hours of March 29, the agency said. In that instance, a controller in Fort Worth had to try repeatedly to raise the Lubbock controllers in order to hand off control of an inbound aircraft. The controllers also failed to hand off a plane departing Lubbock to the Fort Worth radar center, FAA said.
The latest cases follow three previously disclosed incidents in which controllers have been suspended, including two episodes of controllers sleeping on duty.
"Air traffic controllers are responsible for making sure aircraft safely reach their destinations. We absolutely cannot and will not tolerate sleeping on the job," FAA Administrator Randy Babbitt said in a statement Wednesday.
Babbitt and Paul Rinaldi, the president of the National Air Traffic Controllers Association, the union that represents FAA's more than 15,000 controllers, will be visiting airports and radar facilities around the country next week "to reinforce the need for all air traffic personnel to adhere to the highest professional standards," FAA said in a statement.
The FAA last month put two controllers on duty during the midnight shift at the Reno-Tahoe airport but went back to one controller several days later after implementing new procedures, FAA spokesman Ian Gregor said. Reno is one of the airports that will now get a second controller.
Airport chief Krys Bart said the pilot of the medical flight - a Piper Cheyenne with seating for five - and airport staff had tried to contact the controller multiple times without success. The FAA said the pilot was in contact with regional radar controllers in northern California during the landing.
"The pilot evaluated the airfield. The weather was clear. The aircraft did land without incident," Bart said.
It was not immediately clear where the flight was coming from.
The incidents come nearly five years after a fatal crash in Kentucky in which a controller was working alone. Investigators said the controller in Kentucky was most likely suffering from fatigue, although they placed responsibility for the crash that took 49 lives on the pilots.
The new disclosures drew rebukes from the chairmen of the Senate and House committees that oversees FAA's budget.
"I just got off the phone with the FAA and told the administrator that I am sick of this," said Sen. Jay Rockefeller, D-W.Va., chairman of the Commerce, Science and Transportation Committee.
But Rep. John Mica, D-Fla., chairman of the House Transportation and Infrastructure Committee, objected to adding more controllers at airports where nighttime traffic is light.
"Only in the federal government would you double up on workers, averaging $161,000 per year in salary and benefits, that aren't doing their job," Mica said in a statement. "This staffing increase misdirects our resources and focus away from congested air traffic control facilities," he said.
FAA said the airport towers where a second controller will be added to the midnight shift are Akron-Canton, Ohio; Allegheny, Pa.; Andrews Air Force Base, Md.; Burbank, Calif.; Duluth, Minn.; DuPage, Ill., Fargo, N.D.; two airports in Fort Lauderdale, Fla.; Ft. Worth Meacham, Texas; Grant County, Wash.; Kansas City, Mo.; Manchester, N.H.; Omaha, Neb.; Ontario, Calif.; Reno-Tahoe, Nev.; Richmond, Va.; Sacramento, Calif.; San Diego, Calif.; San Juan, Puerto Rico; Terre Haute, Ind.; Teterboro, N.J.; Tucson, Ariz.; Willow Run, Mich.; Windsor Locks, Conn., and Youngstown, Ohio. A second nighttime controller was also added at an approach control facility in Omaha.
The Associated Press contributed to this report