The head of the US air traffic control has resigned after a series of incident in which controllers sleeping on the job.

Hank Krakowski was director of the Federal Aviation Administration’s Air Traffic Organization, which is in charge of more than 9 million departures and arrivals at more than 400 airports annually.

The FAA has launched an investigation into why at least four controllers fell asleep at work, including one who was out of radio contact while a medical flight was trying land in Nevada.

FAA Administrator Randy Babbitt said in a statement: “Over the last few weeks, we have seen examples of unprofessional conduct on the part of a few individuals that have rightly caused the travelling public to question our ability to ensure their safety.
This conduct must stop immediately.”

Suspected errors by controllers in 2010 rose to 1,887 from 1,233 in 2009, according to the FAA. More than half were classed as relatively minor, but reports in the most severe category rose to 43 from 37.

Last Monday, a controller in Seattle, Washington state, who was already facing disciplinary action for falling asleep twice during an evening shift in January, was suspended after again falling asleep.

Other incidents were reported in Washington DC, where an American Airlines flight and a United Airlines flight landed without clearance after a local controller fell asleep, and in Lubbock, Texas, where two controllers were suspended after failing to hand over control of a departing plane to air traffic control in Fort Worth.

David Grizzle, the FAA’s chief counsel, was named acting chief operating officer until a permanent replacement for Mr Krakowski is found.