Air traffic controllers' work schedules can lead to chronic fatigue, according to a study conducted by NASA researchers for the Federal Aviation Administration that was completed in December 2012 and published online Monday.

The Associated Press, which first reported on the findings, says the study came about after the National Transportation Safety Board made a recommendation to the FAA and the National Air Traffic Controllers Association that they change controllers' schedules to provide more time to sleep.

The news service adds:

"In the field study, researchers concentrated on controllers who worked a schedule known as the 'rattler' in which controllers squeeze five eight-hour shifts into four 24-hour periods by cutting the turnaround time between shifts to as little as eight hours. Some controllers like the schedule because it gives them a 3-day weekend.

"Controllers participating in the study wore a wrist device that recorded when they were asleep. They also kept logs of their sleep, and were administered alertness tests several times per work shift."

The AP noted that "[FAA] officials had declined to furnish a copy [of the report] despite repeated requests over the past three months, including a Freedom of Information Act filing."

Here are a few key things to know from the 270-page study:

The study makes 17 recommendations to the FAA, the AP notes.

You can read the entire report here.

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