New regulations intended to keep air traffic controllers from dozing off on duty have been violated nearly 4,000 times, according to internal Federal Aviation Administration documents.

After a controller fell asleep last year in the tower at Reagan National Airport, it emerged that such lapses were commonplace at airports across the country, and the FAA said it would act to curb the problem.

But a memo to more than 400 frontline FAA managers this month said a five-month internal review earlier this year uncovered repeated violations of a requirement that controllers have at least nine hours off between shifts. More than half of the airport control towers were found to have violated the rule at least once. One facility broke the rule scores of times.

The FAA suspended or fired several controllers for sleeping on the job last year, and the controversy contributed to the ouster of the head of the FAA’s air traffic control organization.

Among those incidents was one at Reagan National Airport when the pilots of two late-night jet liners had to land on their own after the controller supervisor who was the lone man on duty fell asleep. A Knoxville controller working the overnight shift made a bed for himself and slept during a five-hour period when seven planes landed. And a controller at a Nevada airport slept as a medical flight sought to land with a sick patient.

A scheduling practice that let controllers pack a full work week into just four days was singled out as the primary reason they were coming to work too tired to stay awake.

U.S. Transportation Secretary Ray LaHood said he was outraged and put an immediate end to solo overnight shifts. The FAA ordered that controllers have a minimum of nine hours off before a day shift and prohibited a popular shift- swapping practice that violated that rule.

“A vast majority of employees are meeting the requirement for nine consecutive hours of rest between shifts,” said David Grizzle, FAA chief operating officer. “There are 12,000 shifts per month across the country, and in some cases, employees were [arriving] a few minutes early.”

After discovering the violations recently, Grizzle said the FAA was updating its timekeeping software to prevent controllers from clocking in without nine hours’ rest.

LaHood last year instructed the FAA to work with the union on rules to ensure that the controllers who manage 24,000-27,000 commercial flights a day to arrive at work well rested.

Almost a year ago, the agency and the National Air Traffic Controllers Association (NATCA) announced an agreement that required controllers to notify their supervisor if they were too tired to do their jobs. They also were allowed to ask for time off if they were too fatigued to work air traffic, were permitted to read on the job and were given rest breaks.

“These standards are based on a little more than guess work, so you’d think they’d want to adhere to them,” said Gerald Dillingham, director of civil aviation for the U.S. Government Accountability Office, whose office has studied aviation fatigue issues.

Dillingham described the nine-hour break between shifts as “sort of minimalist” and an important standard, but said he wasn’t surprised to learn it was being violated.

“The controllers liked to work it so they’d get these long weekends,” he said. “Once the Hill gets wind of this they may want us to look into it.”

Since the beginning of the year, internal information indicates the nine-hour minimum rule has been violated thousands of times, sometimes by a matter of minutes and other times by more than that.

In a June 4 memo signed by officials from the FAA and the union, supervisors were told of numerous violations and reminded that all controllers must have nine hours off before a day shift.

Scheduling needs to be flexible to meet the air traffic system’s demands, and over the years one of the most popular schedules became what was known as the 2-2-1. It was favored by many controllers because it compacted their workweek and created a weekend of at least three days.

Under it, a controller began the work week with two evening shifts, did a quick turnaround to a pair of day shifts and then did another quick turnaround before an overnight shift.

Those quick turnarounds — usually just eight hours — were blamed for controller fatigue, particularly when the final quick turnaround came at the end of the work week and just before an overnight shift.

Most of the controllers who were disciplined or fired for sleeping were working overnight shifts.

Under the guidelines developed after the controllers were found sleeping, nine hours of rest are required before day shifts but only eight hours are mandated prior to the final overnight shift.

That overnight shift, commonly known as the “mid” or midnight shift, routinely consists of a flurry of activity when it gets underway at 10 p.m. as most of the night’s last planes come in, but that tapers off by midnight.

“After doing this for years I know this much: It doesn’t matter if I have eight or nine hours between shifts,” said one veteran controller who asked not to be named so that he could speak candidly. “No matter what, I am tired on the mid shift. Not to say that I cannot function, just that I am not totally on my game.”

The controller described the nine-hour requirement as “more of a nuisance than a true answer to fatigue mitigation.”

“With the schedule we work, there is always someone yawning aloud, including me,” the controller said. “But we plug away and get the job done to the best of our ability, no matter if we’re a little tired.”