Stinson 108-1 N97946 accident near Concrete, Washington

Probable cause

The loss of engine power during initial climb due to the pilot's improper exhaust system maintenance, which resulted in restriction of the carburetor's air intake.

NTSB analysis

For 7 years, the pilot had performed maintenance, which included 100-hour and annual inspections of his airplane's engine. On an undetermined date, a rope-like material had been placed between the exhaust's heater shroud and muffler. At an undetermined date/time, this material became separated from its installed location. During takeoff on the accident flight, the rope-like material became lodged in the carburetor's air intake. This resulted in restricting the flow of air into the carburetor, and the engine lost power. It was a dark night, and the airplane collided with trees during the ensuing forced landing. Toxicology results were consistent with the relatively recent use of diphenhydramine, an over-the-counter antihistamine with sedative and impairing effects, and propoxyphene, a prescription narcotic medication with impairing effects. The levels detected on toxicology evaluation were not consistent with impairment at the time of the accident. The pilot had indicated to the FAA a history of diabetes and kidney stones, but not the use of diphenhydramine or propoxyphene, and it could not be determined whether medical conditions or the use of medication may have played a role in his decision to insert the rope-like material in the engine compartment.

Text from the NTSB. Open the NTSB docket for WPR09LA022 for the full record.