WASHINGTON — Air traffic controllers are still working schedules known as "rattlers" that make it likely for them to get little or no sleep before overnight shifts, more than three years after a series of incidents involving controllers sleeping on the job, according to a government report released Friday.

A report by the National Research Council expressed concern about the effectiveness of the Federal Aviation Administration's program to prevent its 15,000 controllers from suffering fatigue on the job, a program that has been hit with budget cuts. 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 work schedules affect controller performance.

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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.

The committee stressed its concern that controllers are still working schedules that cram five eight-hour work shifts into four 24-hour periods. The schedules are popular with controllers; at the end of their 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."

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.

A view from the control tower at Los Angeles International Airport (LAX). Image: Reed Saxon/Associated Press

FAA officials didn't immediately respond to a request for comment on the report.

The National Air Traffic Controllers Association defended the scheduling, citing the 2009 study that hasn't been publicly released. The union said in a statement that NASA's research showed that "with proper rest periods," the rattler "actually produced less periods of fatigue risk to the overall schedule."

In 2011, FAA officials and then-Transportation Secretary Ray LaHood promised reforms after a nearly a dozen incidents in which air traffic controllers were discovered sleeping on the job or didn't respond to calls from pilots trying to land planes late at night. In one episode, two airliners landed at Washington D.C.'s Reagan National Airport without the aid of a controller because the lone controller on the overnight shift had fallen asleep. In another case, a medical flight with a seriously ill patient had to circle an airport in Reno, Nevada, before landing because the controller had fallen asleep.

Studies show most night shift workers, not just controllers, face difficulties staying awake regardless of how much sleep they have gotten. That's especially true if they aren't active or don't have work that keeps them mentally engaged. Controllers on night shifts often work in darkened rooms with frequent periods of little or no air traffic to occupy their attention, conditions scientists say are conducive to falling asleep.

"We all know what happens with fatigue," said Mathias Basner, an assistant professor at the University of Pennsylvania medical school and the sleep expert on the committee. "The first thing you expect to see is attention going down, reaction time slows, you have behavioral lapses or micro-sleeps. ... If you have to react quickly in that situation, that is problematic."

After the 2011 incidents with falling asleep, the FAA stopped scheduling controllers to work alone on overnight shifts at 27 airports and air traffic facilities and increased the minimum time between work shifts to nine hours.

Another change was the creation of a "fatigue risk management program" for controllers. However, budget cuts "have eliminated the program's capability to monitor fatigue concerns proactively and to investigate whether initiatives to reduce fatigue risks are providing the intended benefits," the report said.

Basner said the FAA was making no effort to determine whether there is a correlation between work schedules and controllers errors. For example, there were near collisions between airliners near Honolulu and Houston recently.

On April 25, 2014, a controller failed to notice when two airliners were on a collision course in Honolulu. The pilot of one of the aircrafts had to initiate an abrupt dive to avoid an accident.

In Houston, two planes almost collided during takeoff — the aircraft came within a few hundred feet of each other when a controller told one plane to turn right when it was supposed to turn left.

The FAA and the controllers' union have established a program that encourages controllers to report errors by promising they won't be penalized for honest mistakes. The reports are entered into a database that the agency is supposed to use to spot trends or problem areas. But controllers are sometimes too busy to file reports, and the report forms don't seek information on the controller's schedule or other details that might be used to determine whether schedules are contributing to errors, Basner said.

When FAA officials were asked about this, they indicated "they didn't see the necessity to analyze the data that way," he said.

The committee also thought it was "a bit strange" that FAA officials wouldn't show them their 2009 study conducted with NASA, Basner added.

"You would think you would get 100% support, but we didn't get it."

Additional reporting by Mashable