What happened
During a night shift at the Cairns Terminal Control Unit (TCU), an approach controller was discovered asleep at their workstation shortly before a shift handover. At approximately 0500, the controller was found in a position involving lying across two chairs under a blanket. Data from the air situation display showed no system interactions for roughly 15 minutes prior to the discovery. While the controller had set the headset volume to maximum and enabled the loudspeaker to alert themselves or colleagues to incoming traffic, the lack of aircraft in the airspace at that hour contributed to the situation.
The investigation
Investigators examined the controller's recent work history and identified several physiological and situational stressors. The controller was working during the circadian low, a period of high biological sleep drive. At the time of the incident, the controller was on their third consecutive night shift and their seventh night shift within a nine-day period. Furthermore, the controller had experienced insufficient sleep over the preceding 48 hours, likely carrying a significant sleep debt into the shift.
Beyond individual fatigue, the investigation looked into the broader fatigue risk management system used by Airservices Australia. It was found that while strategic rulesets were in place, staff under-resourcing led to gaps in master rosters. To address these gaps, the organization relied heavily on tactical roster management, which failed to effectively identify or mitigate the risks of cumulative fatigue caused by schedule changes.
Findings
- The controller was experiencing very low workload with no expectation of incoming traffic.
- The controller had engaged in practices that increased sleep risk, such as failing to vary posture and using blankets to facilitate sleep.
- The fatigue assessment and control tool (FACT) was ineffective in this instance because supervisors did not recognize low workload as a specific fatigue hazard.
- Cumulative fatigue arising from roster changes was not adequately managed due to an over-reliance on tactical roster adjustments.
Safety message
- The effectiveness of fatigue assessment tools is limited if supervisors do not identify low workload as a significant fatigue hazard.
- Over-reliance on tactical roster management to fill gaps caused by under-resourcing can prevent the effective identification of cumulative fatigue risks.