WASHINGTON (AP) – The Federal Aviation Administration is immediately adding a second controller at night at 26 airports and a radar facility after finding two more cases of controllers sleeping on duty.

Transportation Secretary Ray LaHood’s announcement Wednesday came hours after a medical flight carrying at least three people landed at Reno-Tahoe International Airport in Nevada without assistance because the pilot was unable to raise a controller in the airport tower. FAA said in a statement that the controller, who has been suspended, had fallen asleep. The incident occurred at 2 a.m. PDT, when the controller was alone on duty.

Another controller, at Boeing Field-King County International in Seattle, has also been suspended for falling asleep during his morning shift on Monday, FAA said. That controller was already facing disciplinary action for falling asleep on two separate occasions during an early evening shift in January, the agency said.

Two controllers at the airport in Lubbock, have been 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.

“I am totally outraged by these incidents. This is absolutely unacceptable,” 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.”

The latest spate of incidents began last month when two airliners landed at Washington’s Reagan National Airport without assistance from the tower after pilots were unable to raise the lone supervisor on duty at midnight. The supervisor later acknowledged he had fallen asleep. A second controller has been added to the midnight shift at Reagan National.

Last week, FAA Administrator Randy Babbitt told a congressional panel that FAA is seeking to fire a controller in Knoxville, Tenn., who deliberately slept for five hours while he was supposed to be manning a radar facility that handles aircraft approaches for the Knoxville airport as well as several other smaller airports in the region. The lone controller on the midnight shift in the airport’s tower wound up performing both his job of landing planes as well as the sleeping controller’s job of handling approaches.

“Air traffic controllers are responsible for making sure aircraft safely reach their destinations. We absolutely cannot and will not tolerate sleeping on the job,” Babbitt said in a statement Wednesday.

FAA also suspended an air traffic controller at a radar facility in central Florida last month for actions that brought a Southwest Airlines Boeing 737 and a small private plane too close together.

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.