MIA00LA010 · Cessna 150M

During cruise flight, the engine began to run rough. The pilot initiated a 180-degree turn to return then 1-2 minutes later, thick white smoke was 'pouring' from under the left side of the instrument panel in the area of the magneto switch. All electrical equipment was turned off including the magneto switch. The airplane nosed up briefly after touchdown in a field during the forced landing. Heat damage to electrical wires in the engine compartment was noted. The aft end plate P/N 0450338-18 of the right muffler was not in place and was not located; only a peripheral flange remained. Examination of the right muffler P/N 0450400-26 revealed perforation of the tube and thinning of the material near the fracture surface of the end plate. There was no record indicating that the right muffler had been replaced or repaired since the airplane was manufactured. Four days after the accident, the FAA found a mechanic making an entry in the maintenance records indicating completion of an annual inspection that he performed approximately 8 months earlier. The mechanic reported using 14 CFR Part 43, Appendix D and his own checklist as a reference. The airplane had accumulated approximately 37 hours since the last annual inspection, and 3,781.4 hours since manufacture, at the time of the accident. Cessna recommends inspection of the exhaust system every 50 and 100 hours, and also a submerged pressure test of the muffler when fumes are detected in the cabin or for a thorough inspection.

Verbatim NTSB analysis and probable cause from the NTSB dataset