Date: 202108
Local time of day: 1801-2400
Flight conditions: VMC
Aircraft: Fairchild Swearingen Undifferentiated or Other Model
Operator: Air Carrier
Flight plan: IFR
Flight phase: Cruise
Aircraft component: Engine Air Pneumatic Ducting
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Physiological - Other; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Illness / Injury
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: While flying from ZZZ to ZZZ1 I noticed that the left gasper valve in front of my (the captain side) left knee was becoming extremely hot. This temperature; as I could only estimate; to be in excess of 200 degrees Fahrenheit. I know that other captains on the metro liner have complained of similar things happening that could not be solved my maintenance when written up. Due to this; I elected to continue the flight. About 1.3 hours into a 2 hour flight; I started to notice some physiological abnormalities. These abnormalities would include: drowsiness; nausea; light headedness; a slight headache; and tingling in the end of my left thumb. At this point I checked my cabin altitude and I was holding a 9;000 foot cabin altitude at FL80. Regardless of my cabin altitude; I donned my oxygen mask and started troubleshooting my symptoms. I started to consider the possibility of a bleed leak that could have also been reason the gasper valve and left paneling in the cockpit got so hot. Now that I was daily sure of my mechanical diagnosis; I turned the left bleed off and descended to 10;000 feet. I used the onboard oxygen as much as I could until landing in ZZZ1. The landing was uneventful but my nausea and headache persisted. After I wrote the aircraft up in detail I began driving myself to get medical evaluation. After seeing the doctor; which took 5 hours in the waiting room; he suspected that I had carbon monoxide poisoning to a degree; although it was no longer in my bloodstream when they were able to get the blood sample due to the time that elapsed between incident and blood draw.In these types of situations; the event can be bypasses by a mechanical fix. However; I do personally feel like some people; due to the nature of the job; let certain things slide to meet 'on time performance' or 'a completion factor. These types of thing just evolve into a more serious issue down the road. In addition to this; at times I feel like there has been a culture set forth that teaches 'these are old planes; they do this or that from time to time; its no big deal.' This; in my opinion just leads to mechanical irregularities that over time get worse; instead of fixing a problem early on that may have delayed cargo; or grounded a plane in an outstation that would be of a large inconvenience to fly out mechanics.




Synopsis: Captain reported an airborne fume event in which he experienced persistent physiological symptoms.