Accident Overview
A Piper PA-23, occupied by a pilot and a pilot-rated passenger in the right seat, departed on a local round robin flight. The aircraft was not equipped with wing or propeller deice or anti-ice systems. Climbing to 11,000 feet, the pilots encountered a vibration and a loss of left engine power. They initiated a return to Missoula for landing. Unable to maintain altitude with partial power, a forced landing was executed short of Runway 25 at the Missoula Airport.
Post-Impact Events
Prior to the forced landing, an attempt was made to lower the landing gear. During the rollout, the nose landing gear collapsed after striking a gopher hole.
Weather and Examination Findings
Missoula reported several scattered, broken, and overcast cloud layers below 11,000 feet during the afternoon, with the surface temperature peaking at 44 degrees Fahrenheit. After the accident, airport ARFF personnel observed ice detaching from the aircraft wing(s). Subsequent inspection by FAA personnel reported that the left induction air filter was heavily soaked with water.