NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The airplane was observed to fly a circling maneuver, and then dive vertically into the ground with the engine running. Forensic toxicology revealed 31 percent carbon monoxide in the pilot's blood. Metallurgical examination of the exhaust muffler and heat exchanger assembly revealed the wall of the muffler was fractured through in the area where the exhaust pipe was welded to the muffler canister. Fracture surfaces darkly colored by corrosion were observed at the edge of the weld bead around the exhaust port over a circumference of approximately 180 degrees, and along several cracks branching outward from the weld bead. Fracture surfaces that displayed no corrosion branched out circumferentially from the corroded fracture surfaces on either end of the exhaust outlet. A review of Federal Aviation Administration Advisory Circular AC65-12A revealed in Chapter 2, Induction and Exhaust Systems, Exhaust System Repairs: "It is generally recommended that exhaust stacks, mufflers, tailpipes, etc., be replaced with new or reconditioned components rather than repaired".