What happened
On March 15, 1997, a Finnair flight, operating as FIN-582, was traveling from Stockholm-Arlanda to Helsinki. The aircraft, a DC-9-51 with registration OH-LYU, was carrying a crew of six and 94 passengers. During the flight, the captain began experiencing symptoms of illness following a breakfast in Stockholm. As the flight progressed toward Helsinki, the captain's condition deteriorated, characterized by severe diarrhea and feverish sensations.
While descending toward Helsinki, the captain's physical state worsened to the point that he could no longer maintain flight duties. He relinquished control of the aircraft to the first officer and reclined his seat to rest. During this period, the captain experienced a significant reduction in consciousness, described as a dream-like state, accompanied by dilated pupils and nausea. The first officer, noticing the captain's deteriorating condition, notified Helsinki Approach and requested assistance from the cabin crew to provide emesis bags.
Despite the captain's incapacitated state, the first officer successfully managed the approach and landing procedures alone. The first officer utilized the aircraft's nosewheel steering and rudder pedals to navigate to a high-speed taxiway, as the captain was unable to reach the left-side steering wheel. Following the landing, the captain's condition improved sufficiently for him to assist in taxiing the aircraft to the gate.
The investigation
The investigation examined the medical state of the captain, his nutritional and fluid intake, and the physiological mechanisms leading to the event. Investigators reviewed flight logs, radio communications, and interviews with the crew. The investigation also looked into the environmental factors, such as the meal service provided to the crew in Stockholm, to determine if foodborne illness was a factor.
Findings
- The captain was suffering from a viral infection, which caused significant fluid loss through diarrhea.
- Severe dehydration was a primary factor, as the captain had consumed very little fluid both the previous evening and on the morning of the flight. It was estimated that while he had consumed only about 900 ml of fluid, his losses due to infection and normal bodily functions were between 1500 ml and 2300 ml.
- The combination of the infection, significant fluid loss, and the physiological effects of prolonged sitting (which caused blood to pool in the lower extremities) led to a drop in blood pressure.
- The failure of the body's circulatory regulation mechanisms resulted in the observed reduction in the captain's level of consciousness.
- The investigation concluded that the meal provided to the crew was not the source of the illness, as the components were prepared by the same staff and the symptoms were consistent with a virus also affecting the captain's family.
Safety action
- The investigators recommended that airlines and aviation companies provide training on the possibility of sudden incapacitation and implement instructions for its prevention and management within their safety training programs.