Work schedules of air traffic controllers' (ATC) have led them to suffer from chronic fatigue that decreased their efficiency, a study by the US Federal Aviation Administration (FAA) has revealed.
The study findings had not been made public by the US Government for several years, the Associated Press (AP) reported.
Carried out by Nasa, the study was drafted on 1 December, 2011. It has also revealed that tight schedules have led to an endangering of the safety of the country's airspace.
The study interviewed around 3,268 controllers on their work schedules and sleeping habits and found that two out of ten controllers had committed significant errors including bringing planes too close together.
The reason for half of the errors was claimed to be fatigue.
One third of the controllers said that fatigue posed a high level of risk.
More than six in every ten controllers sampled said that they had fallen asleep or experienced an attention lapse while driving to or from their shifts.
The study said: "Chronic fatigue may be considered to pose a significant risk to controller alertness, and hence to the safety of the air traffic control (ATC) system."
The study made 17 recommendations to the FAA that included the discontinuance of mandatory six-day schedules for controllers as nearly 30% of them who worked the six-day schedules had confessed to having committed an error in the previous year.
However, three years after the study was carried out, six-day schedules are still being carried out, reported AP.