What happened
A scheduled commuter flight was approximately 30 minutes into its route, maintaining a cruise altitude of 13,000 feet MSL, when both pilots began experiencing symptoms of dizziness and disorientation. The crew utilized supplemental oxygen, which caused the symptoms to dissipate. The aircraft subsequently completed a normal landing at its intended destination roughly 10 minutes after the onset of the symptoms. One passenger also indicated they may have experienced dizziness.
The investigation
An examination of the aircraft, cargo, luggage, and crew was conducted following the event. Investigators found no evidence of an issue within the aircraft or its contents. Neither crew member exhibited physical manifestations such as irritation or the presence of any detectable odors. No other aircraft operating in the same area at the time reported experiencing similar difficulties.
A follow-up test flight was performed using the same aircraft, crew, route, and altitude. During this flight, an industrial hygienist conducted various tests, all of which yielded negative results. Furthermore, monitoring of the crew and the aircraft for several months following the incident provided no additional information regarding the cause of the disorientation.