US officials announced new shift rules for air traffic controllers as part of a "zero tolerance" policy to stop alarming numbers of staff from falling asleep on the job. Transportation officials monitoring some of the world's busiest air traffic have been red-faced as case after case of workers snoozing in US airport towers came to light in recent weeks, in some incidents leaving pilots of passenger jets to land unassisted in Washington. The head of US air traffic control resigned Thursday, and the Federal Aviation Administration (FAA) vowed a major shake-up to win back public trust in its safety. "We expect controllers to come to work rested and ready to work and take personal responsibility for safety in the control towers," Secretary of Transportation Ray LaHood in a statement announcing the new rules. "We have zero tolerance for sleeping on the job," he said. "Safety is our top priority and we will continue to make whatever changes are necessary." The new regulations, which have already been implemented, require the country's 15,000 air traffic controllers to have at least nine hours off between shifts -- one more than the current eight-hour minimum, FAA said. The rules also restrict shift-swapping in order to prevent short down-time between shifts, and ban controllers from switching to unscheduled midnight shifts following a single day off. "Research shows us that giving people the chance for even an additional one hour of rest during critical periods in a schedule can improve work performance and reduce the potential for fatigue," FAA administrator Randy Babbitt said in the statement. FAA managers, too, are now required to schedule their own shifts in a way that would assure greater coverage in early morning or late night hours. Babbitt and other officials will criss-cross the country in the coming week to meet controllers in several airports, and the FAA is launching a "fatigue education program" to alert workers about fatigue risk, the agency said. Several recent cases have highlighted the alarming safety lapses at major American airports, and officials have scrambled to appear on top of the situation. "I don't know when I've ever been madder. I'm outraged about this," LaHood told Fox News Sunday. "I want the flying public to know we're doing everything we can, 24/7 to correct this problem." President Barack Obama recently sought to reassure Americans that officials had things "under control," but he told ABC News that he was upset over individuals who "let a lot of people down when they fell asleep on the job." Last month in Washington, just a few miles from the White House, two jets carrying a total of 165 people were forced to land at Reagan National Airport without help because the lone controller on the night shift had fallen asleep. After that highly publicized incident, LaHood called on Babbitt to review airport tower staffing levels and ordered two controllers to be placed on the night shift at the Washington airport. At least six incidents of controllers sleeping on the job have been made public in recent weeks. Earlier this month, a controller at Reno-Tahoe International Airport in Nevada fell asleep, forcing a medical plane carrying an ill patient to land without any guidance. The FAA revealed that a controller at a Seattle airport fell asleep several times, most recently during a morning shift last Monday. And in the latest incident, an air traffic controller in Miami was suspended on Saturday after falling asleep on duty. In 2007 the National Transportation Safety Board recommended a change to controller working hours, and LaHood conceded Sunday on Fox that "the NTSB was probably right." But he rejected allowing tower workers to take naps during their shifts, as recommended by some scientists and allowed in Canada and some European nations. "On my watch, controllers will not be paid to take naps," LaHood said.