The head of the Air Traffic Organization at the Federal Aviation Administration resigned Thursday morning amid recent reports of several controllers sleeping on the job.

Hank Krakowski submitted his resignation to FAA Administrator Randy Babbitt, who said he accepted it.

“Hank is a dedicated aviation professional and I thank him for his service,” Babbitt said in a statement. “Starting today, I have asked David Grizzle, FAA's chief counsel, to assume the role of acting ATO chief operating officer while we conduct a nationwide search to permanently fill the position.” 

Babbitt said recent reports of “unprofessional conduct on the part of a few individuals have rightly caused the traveling public to question our ability to ensure their safety.”

On Wednesday federal officials ended the practice leaving one controller on in airport towers during overnight shifts. The news come as the FAA revealed that a Nevada air traffic controller allegedly fella sleep Wednesday morning as a medical flight carrying a patient tried to land. The plane landed safely at Reno-Tahoe International Airport with the help of a radar controller based in California, the FAA said. The controller was suspended and the incident is under investigation.

However, the incident Wednesday was the fifth time this year that a controller apparently slept while on duty, including at Reagan National Airport, where a controller supervisor was suspended last month after he admitted to napping  in the tower.

The FAA plans to conduct a “top to bottom review” of the nation’s air traffic control system, Babbitt said.

“We are all responsible and accountable for safety–from senior FAA leadership to the controller in the tower,” he said.  “Employees at the FAA work diligently every day to run the safest air transportation system in the world. But I will continue to make whatever changes are necessary to ensure we concentrate on keeping the traveling public safe.”