On November 30, 2000, about 1100 Eastern Standard Time, a Mooney M20C, N942TB, was not damaged during a pilot incapacitation event near Hazard, Kentucky. The certificated private pilot and pilot rated passenger received minor injuries, and two passengers were not injured. Visual meteorological conditions prevailed for the flight that departed Lynchburg Regional Airport (LYH), Lynchburg, Virginia; destined for Kyle-Oakley Field (CEY), Murray, Kentucky. An instrument flight rules flight plan was filed for the personal flight conducted under 14 CFR Part 91. The pilot stated that he was in cruise flight at 8,000 feet near Hazard, Kentucky. He began to feel ill, and requested a descent to 6,000 feet. The pilot then began to "go in and out of consciousness." The pilot rated passenger had not flown for over 25 years, but was able to fly the airplane to Big Sandy Regional Airport (K22), Prestonsburg, Kentucky. The pilot rated passenger successfully woke the pilot, and the pilot made an uneventful landing. The pilot stated that he remembered flying a left-hand traffic pattern at K22, but did not remember landing the airplane. The pilot further stated that hospital tests revealed he and the pilot rated passenger had toxic levels of carbon monoxide in their blood. Carbon monoxide was present in the rear seat passengers, but the levels were not toxic. Examination of the airplane revealed a hole in the cabin air scat tubing. The hole was next to the joint that connected the exhaust manifold to the exhaust from the number one cylinder. The joint was not secure, and a gap was visible. Photographs of the engine were forwarded to the airplane manufacturer. The manufacturer stated that sometime during the airplane's history, the scat tubing was misrouted. The tube with the hole, connected the air inlet to the cabin. A second tube connected the air inlet to a heater exchange. The tube with the hole was suppose to be routed underneath the second tube, however, it was resting on top of it. The manufacturer added that the scat tubing was not clamped, but the clamps would only help if the tube was correctly routed. The pilot stated that maintenance work was performed on his airplane prior to the day of the incident. Specifically, a fixed base operator replaced the alternator. However, a Federal Aviation Administration (FAA) inspector stated that the misrouting could have happened during any of several prior maintenance visits. The inspector could not confirm that the most recent maintenance work was the cause of the misrouting. Additionally, he could not confirm when the gap formed in the joint between the cylinder and exhaust manifold. The airplane's last annual inspection was performed on October 28, 2000.