What happened
During a flight from Cairns to Redcliffe, the pilot transitioned from an intended altitude of 10,000 ft to FL 110 to avoid weather conditions. While operating at this higher altitude, the pilot utilized supplemental oxygen only intermittently. During the flight, the pilot became unresponsive for roughly 40 minutes, causing the aircraft to fly past the intended destination. Upon regaining communication with Air Traffic Control, the pilot appeared groggy and struggled to comprehend instructions, exhibiting signs of sleep inertia.
The investigation
The investigation examined the pilot's physiological state and the use of onboard life support systems. Medical specialists reviewed the pilot's oxygen usage and determined that intermittent application was insufficient to prevent the cumulative effects of hypoxia. A review of the pilot's sleep history revealed a significant sleep debt, characterized by inadequate sleep the previous night and a period of disturbed sleep leading up to the flight. While the pilot suggested the warm cockpit environment might have contributed to falling asleep, investigators focused on the physiological impact of sleep deprivation.
Findings
- The pilot failed to maintain continuous use of the supplemental oxygen system while at FL 110, which likely resulted in mild hypoxia.
- The pilot's ability to remain awake was compromised by a combination of fatigue and mild hypoxia.
- The pilot's sleep history indicated chronic fatigue due to long-term sleep restriction and a lack of sufficient rest immediately prior to the flight.
- Factors such as dehydration and diet may have further exacerbated the pilot's physiological vulnerability.