Cessna Stationair/Turbo Stationair 6
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Commercial
Flight Crew Last 90 Days 40; Flight Crew Total 750; Flight Crew Type 65
Physiological - Other
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Illness / Injury
Flight Crew Took Evasive Action; General Maintenance Action
Aircraft; Human Factors
While conducting an aerial survey; operating a Cessna 206; I noticed that the camera crew person; did not respond appropriately to my questioning and had what appeared to be a sense of confusion during the flight. After speaking with camera person; I performed my own self-assessment and decided to descend and land at ZZZ airport.  Below is my summation of the flight. After takeoff; I leveled the airplane at 16;100 feet to start the aerial survey. I checked to see how much oxygen was flowing through my supplemental oxygen cannula and confirmed it to be set at 17;000 feet. I noticed my camera crew person who was sitting in the right seat next to me increasing his oxygen level intake. I asked him if he was OK and he responded; 'I don't know.' I then asked him if we are doing Lidar work. He replied no; why would you ask me that. Shortly thereafter I started to feel uneasy; woozy; felt my heart rate increase; slow to talk and making decisions was a bit more difficult. I decided to increase my supplemental oxygen cannula to 22;500 feet (to increase the oxygen intake). I looked over at the camera person to see how he was doing and noticed what appeared to me a discoloration of his face. At this point I took the following actions; started a descent; turned off the cabin heat; opened the air vents; notified ATC and activated the autopilot for the descent (in the event I passed out). Upon reaching a lower altitude and knowing that I was not going to pass out; I disengaged the autopilot and accelerated the descent to 3;500 feet and continued directly to ZZZ and landed. After speaking with the mechanics; it was learned that the flange was bent causing the number 2-cylinder leaking exhaust gases into the cabin.
Cessna 206 pilot reported executing an immediate descent after feeling woozy and feeling a heart rate increase.  Pilot landed safely and post maintenance inspection revealed the flange was bent causing the number 2 cylinder to leak exhaust gases into the cabin.