What happened
During a cruise flight at an altitude of 9,000 feet MSL, the pilot experienced a loss of power and rough running in the left engine. The pilot initially attempted to resolve the issue by applying carburetor heat, suspecting carburetor icing. When the engine continued to run poorly, the pilot feathered the left propeller and shut down the engine. Following unsuccessful attempts to restart the engine, the aircraft was unable to maintain its altitude. After descending through instrument meteorological conditions (IMC), the pilot determined that the nearby airport was unreachable and performed a forced landing into rough and uneven terrain.
Findings
Post-accident inspections of the engines identified that the alternate air doors were missing from both the left and right engines. While the hinges for these doors remained attached to the carburetors without signs of impact or distortion, the doors themselves were not located at the crash site. The absence of these doors meant that ambient air could enter the carburetor, which prevented the carburetor heating system from functioning correctly. Based on the recorded temperature and dew point, conditions were highly conducive to the formation of induction system icing, which likely contributed to the engine malfunction.