The head of the FAA's air traffic control unit resigned Thursday after a fifth controller was caught dozing while working the graveyard shift, officials said.
"Hank Krakowski has submitted his resignation, and I have accepted it," said Randy Babbit, chief administrator for the Federal Aviation Administration.
A former airline pilot, Krakowski had been the chief operating officer of the FAA's air traffic organization since 2007.
Babbit called the episodes of air traffic controllers sleeping on the job shockingly "unprofessional conduct" and vowed "a top to bottom review."
"This conduct must stop immediately. I am committed to maintaining the highest level of public confidence and that begins with strong leadership," Babbit said.
The announcement came as an air traffic controller was caught dozing early Wednesday as a flight tried to land at Reno-Tahoe International Airport.
It's the fifth time this year that an air traffic controller fell asleep while working alone on the overnight shift.
In response, the Federal Aviation Administration announced that it was putting a second controller in the tower for the late night shift at 26 airports and a radar facility.
"I am totally outraged by these incidents. This is totally unacceptable," said Transportation Secretary Ray LaHood. "The American public trusts us to run a safe system."
Two flights landed unassisted at Washington's Reagan National Airport last month as the air traffic controller snoozed.
A subsequent investigation revealed that similar incidents had occurred this year at airports in Knoxville, Tenn., Seattle and Lubbock, Texas.