A Nevada air traffic controller allegedly fell asleep early Wednesday as a medical flight carrying a sick patient tried to land, leading federal authorities to order an immediate end to the practice of leaving one controller on duty during overnight shifts.

The plane landed safely at Reno-Tahoe International Airport with the help of a radar controller based in California, the Federal Aviation Administration said. The Reno controller was suspended, and the FAA is investigating why there were 16 minutes of silence as the medical flight sought to land.

The air traffic control system has come under scrutiny by the National Transportation Safety Board and Congress after a year in which the number of operational errors recorded by controllers increased by 51 percent. Those errors were failures to keep aircraft at a safe distance while in flight.

The incident Wednesday was the fifth time this year that a controller apparently slept while on duty.

A controller supervisor was suspended last month after he admitted to napping in the tower at Reagan National Airport. The FAA has taken steps to fire a Knoxville radar controller who allegedly used a makeshift bed to sleep while on duty in February.

A Seattle tower controller working with two colleagues Monday was suspended after he fell asleep, the FAA said. According to federal officials, it was the third time the controller had slept on the job.

Two Texas controllers working the midnight shift last month were suspended after they failed to properly hand off a flight departing from Lubbock to radar controllers in Fort Worth, the FAA said. A Fort Worth controller also received no response when he tried to hand off an inbound flight to the Lubbock tower.

It is routine for controllers to work a compressed workweek that includes two evening shifts, a quick turnaround to a pair of day shifts and another quick turnaround to a midnight shift, all separated by eight- to 10-hour intervals. That allows them a three- to four-day weekend.

U.S. Transportation Secretary Ray LaHood, who ordered a nationwide review of controller staffing after the incident at Reagan National, responded to the latest event by ordering a second overnight controller into the 27 towers that still have one controller on duty on those shifts.

“I am totally outraged by these incidents,” LaHood said in a statement. “This is absolutely unacceptable.”

FAA Administrator J. Randolph Babbitt said he would take top FAA officials and leaders of the controllers union on a tour of the nation’s air traffic control facilities next week to “reinforce the need for all air traffic personnel to adhere to the highest professional standards.”

“Air traffic controllers are responsible for making sure aircraft safely reach their destinations,” Babbitt said. “We absolutely cannot and will not tolerate sleeping on the job. This type of unprofessional behavior does not meet our high safety standards.”

U.S. Sen. John D. Rockefeller IV (D-W.Va.), who chairs the Senate transportation committee, said he contacted Babbitt on Wednesday.

“I just got off the phone with the FAA and told the administrator that I am sick of this,” Rockefeller said. “We can’t have an aviation system where some of the people responsible for safety are literally asleep at the switch. This has to stop. The agency needs to do whatever it takes to keep air traffic controllers from sleeping on the job or not treating their responsibilities with the highest level of seriousness and attention.”

Members of the House transportation committee said they planned to hold a private meeting with FAA leaders Thursday to discuss controller errors and incidents of sleeping on the job. Rep. John L. Mica (R-Fla.), chairman of the committee, criticized the staffing decision.

“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,” he said. “This increase in staffing, when there is little to no traffic, also misdirects our resources and focus away from congested air traffic control facilities.”

The issue of fatigue in the towers and radar rooms where controllers work is not new.

In 2007, the NTSB recommended that the FAA work with the union to “reduce the potential for controller fatigue by revising controller work-scheduling policies and practices to provide rest periods that are long enough for controllers to obtain sufficient restorative sleep and by modifying shift rotations to minimize disrupted sleep patterns, accumulation of sleep debt, and decreased cognitive performance.”

The NTSB is investigating the incident at National Airport and says fatigue is one of the issues under review.

The federal air traffic control workforce is undergoing massive turnover that will take several years to complete. It is the legacy of labor strife in 1981, when the controllers went on strike and President Ronald Reagan fired them all.

The thousands of people brought in to replace those strikers are now reaching retirement age. Controllers are required to retire at 56, although they may retire earlier if they have 25 years of service. The FAA began replacing those in the retirement bubble in 2005, and two years ago the agency set a goal of hiring 17,000 controllers by 2017.