WASHINGTON » Air traffic controllers are at greater risk for fatigue, errors and accidents because they work schedules known as "rattlers" that make it likely they’ll get little or no sleep before overnight shifts, according to a government-sponsored report.

Three years after a series of incidents in which controllers were found to be sleeping on the job, a National Research Council report released Friday expressed astonishment that the Federal Aviation Administration still permits controllers to work schedules that cram five work shifts into four 24-hour periods.

The schedules are popular with controllers because at the end of the last shift, they have 80 hours off before returning to work the next week. But controllers also call the shifts "rattlers" because they "turn around and bite back."

The report also expressed concern about the effectiveness of the FAA’s program to prevent its 15,000 controllers from suffering fatigue on the job, a program that has been hit with budget cuts. And the 12-member committee of academic and industry experts who wrote the report at the behest of Congress said FAA officials refused to allow them to review results of prior research the agency conducted with NASA examining how late-night work schedules affect controller performance.

The FAA-NASA research results "have remained in a ‘for official use only’ format" since 2009 and have not been released to the public, the report said.

An example of the kind of schedule that alarmed the report’s authors begins with two consecutive day shifts ending at 10 p.m. followed by two consecutive morning shifts beginning at 7 a.m. The controller gets off work at 3 p.m. after the second morning shift and returns to work at about 11 p.m. the same day for an overnight shift — the fifth and last shift of the workweek.

When factoring in commute times and the difficulty people have sleeping during the day when the human body’s circadian rhythms are "promoting wakefulness," controllers are "unlikely to log a substantial amount of sleep, if any, before the final midnight shift," the report said.

"From a fatigue and safety perspective, this scheduling is questionable and the committee was astonished to find that it is still allowed under current regulations," the report said. The combination of "acute sleep loss" while working overnight hours when circadian rhythms are at their lowest ebb and people most crave sleep "increases the risk for fatigue and for associated errors and accidents," the report said.

Responding to the report, the FAA said in a statement Friday that it is "adding limitations to its shift and scheduling rules."