Cessna 172 N1612F

The pilot, who was also the owner of the airplane, departed the airport, likely to look at property about 240 nautical miles away. Radar track data showed a target correlated to be the accident airplane after its departure. About 1 hour into the flight, the airplane turned west southwest in a meandering track for about 10 miles, then it made a right turn to the north and completed several left 360° turns, before turning back to the east and completing two additional right 360° turns. The airplane proceeded to the north briefly, completing several 360° turns before continuing into 13 360° right turns that progressed in an easterly direction until radar contact was lost near the accident site. Two witnesses observed the airplane flying low just before the accident, and another witness stated that it was circling and then descended below the tree line. Postaccident examination of the airframe and engine revealed no preimpact mechanical anomalies that would have precluded normal operation. However, examination of the muffler assemblies revealed that the right muffler exhibited cracks and through-thickness metal wastage. Fractures associated with the separation of the aft face with inlet tube exhibited largely oxidized fracture surfaces and thinned walls. The center inlet tube was separated from the rest of the muffler due to loss of mechanical integrity from metal wastage. Holes and wall thickness loss were also noted around the muffler body, which likely led to an escape of exhaust gasses and associated carbon monoxide entering the cabin during the flight. Toxicology testing performed postaccident identified 48 to 61% carboxyhemoglobin in cavity blood. Levels of carbon monoxide of 40% and above lead to confusion, seizures, loss of consciousness, and death. Although there was a postcrash fire, the pilot sustained severe impact-related injuries and would not have been breathing after impact. While postaccident toxicological testing also detected the presence of potentially impairing medications, it is most likely that the pilot experienced carbon monoxide poisoning during the flight when carbon monoxide entered the cabin from the degraded right muffler. The carbon monoxide poisoning led to the pilot’s impairment/incapacitation and his inability to control the airplane, as demonstrated in the airplane’s erratic flightpath during the flight. The pilot’s underlying cardiac disease would have increased his susceptibility to the effects of the carbon monoxide poisoning. According to the airplane’s maintenance records, the left muffler was replaced about 10 years before the accident; however, there was no documentation that showed installation of, or maintenance performed to, the right muffler. At the time of the accident, the airplane was overdue for an annual inspection. Had the pilot had the airplane inspected, it is possible that the deteriorated condition of the right muffler might have been detected and corrected.

Quoted verbatim from the NTSB record.