Incident Overview
An aircraft returning to its home airport experienced a catastrophic failure when the pilot became incapacitated due to carbon monoxide (CO) fumes originating from the engine's muffler heat exchanger. The heat control knob was found in the "On" position. During the final 15 minutes of flight, radar data indicated the aircraft executed several meandering 360-degree turns before colliding with terrain.
Post-Impact Examination
Following the impact, a thorough examination of the engine's muffler revealed a crack traversing the entire circumference, located just aft of its forward flange. This crack allowed exhaust gases, including carbon monoxide, to enter the cabin heating system.
Inspection History
The aircraft's last annual inspection was completed on February 1, 2005. The Federal Aviation Administration (FAA), in Federal Aviation Regulation Part 43: Maintenance, Preventive Maintenance, Rebuilding, and Alteration, Appendix D, provides guidelines for annual inspections. Section (d)(8) specifically addresses exhaust stacks, requiring checks for cracks, defects, and improper attachment.
Additionally, the aircraft manufacturer provides a checklist for the annual inspection in the aircraft's Service Manual. In the section for the Engine Compartment, item #12 directs inspectors to examine the exhaust system for security, leaks, cracks, and burned-out spots, with a reference to Paragraph 12-74, "Inspection of the exhaust system."
Findings
The investigation determined that the muffler crack had likely developed over time, allowing carbon monoxide to enter the cabin. The pilot's incapacitation prevented normal flight control, leading to the erratic flight path and eventual terrain impact.