An air traffic controller found asleep near the end of their shift had worked multiple consecutive nights, resulting in sleep debt, an investigation has found.
The Brisbane controller, who was in charge of Cairns airspace, was found by a colleague laying across two chairs with a blanket covering them at 5.15am on December, 2022.
They were working their seventh night shift in nine days and by the end of the block of shifts, had completed 10 night shifts in 12 days.
Several factors contributed to the controller failing asleep, the Australian Transport Safety Bureau investigation found.
"These included the time of day, the very low workload in their sector, a roster pattern with multiple consecutive night shifts, and the controller increasing their risk of falling asleep by lying across two chairs, not moving, and not undertaking activities to maintain mental alertness," ATSB Chief Commissioner Angus Mitchell said.
When the controller was found, there was no traffic in their airspace, which was usual for that time of day, and there were no scheduled flights until after their shift.
But the investigation noted that if the controller had been woken by a radio broadcast, they may have experienced "sleep inertia", with the risk of delayed communications or incorrect actions, affecting their ability to manage any conflicts.
"There were no negative consequences from this occurrence, but it does highlight areas for improvement in work scheduling and fatigue risk management," Mr Mitchell said.
The investigation also identified issues relating to broader fatigue management.
While no findings were made against the controller, Airservices has increased its overall number of air traffic controllers.
It has also developed additional guidance and training on the fatigue risk assessment process, including information on how low-traffic situations should be treated as high-risk.
"Fatigue remains one of the most relevant ongoing concerns for safe transport, despite increased awareness across the transport sector," Mr Mitchell said.
"We urge transport operators to investigate fatigue events to identify and remedy deficiencies in work scheduling, fatigue risk management processes and risk controls."
