Incident Description
A scheduled commuter flight encountered an unusual situation approximately 30 minutes after departure. While cruising at 13,000 feet MSL, both pilots reported feeling dizzy and disoriented. The crew donned supplemental oxygen, and their symptoms subsided. The flight continued to its intended destination and landed normally about 10 minutes following the onset of the symptoms.
Investigation
Investigators examined the aircraft, the crew, luggage, and cargo, but found no evidence of any problem. Neither crew member reported physical manifestations such as unusual smells or irritation. One passenger indicated a possibility of dizziness, but no other aircraft in the area at the time reported any difficulties.
A test flight was conducted with the same crew, aircraft, route, and altitude. During this flight, an industrial hygienist performed various tests, all with negative results. Additionally, the crew and aircraft were tracked for several months afterward, but no further insight was gained.
Conclusion
The investigation did not identify a specific cause for the dizziness experienced by the pilots. The incident remains unexplained.