What happened
A pilot and a pilot-rated passenger departed on a local round robin flight in a Piper PA-23. During the climb to 11,000 feet, the crew encountered vibration and a loss of power from the left engine. The aircraft was not equipped with wing or propeller deice/anti-ice systems. At the time, Missoula reported several layers of scattered, broken, and overcast clouds below 11,000 feet, with surface temperatures peaking at 44 degrees Fahrenheit.
Following the loss of power, the crew initiated a return to Missoula for landing. However, unable to maintain altitude using only partial power, the crew executed a forced landing short of runway 25 at the Missoula Airport. During the rollout, the nose landing gear collapsed after striking a gopher hole. The occupants were not injured.
The investigation
Airport ARFF personnel observed ice detaching from the aircraft wings following the accident. Subsequent inspections by FAA personnel revealed that the left induction air filter was heavily soaked with water.