Background
Prior to departure, the pilot contacted a flight service station and received a weather briefing. The briefing included current conditions along the route and an AIRMET advising occasional moderate rime or mixed icing in clouds and precipitation below 20,000 feet. The freezing level was reported at or near the surface.
Flight Sequence
Approximately one hour into the flight, while at 8,000 feet, the pilot informed air traffic control (ATC) that a descent was necessary. The pilot stated that ice accumulation was suspected and that an engine problem had developed. ATC provided vectors to a nearby airport. However, the pilot was unable to maintain altitude, and the aircraft subsequently struck terrain approximately seven miles from the airport.
Examination Findings
Post-crash examination of the wreckage revealed that the left engine air filter was partially covered with ice approximately one-half inch thick. This filter was recovered after the post-crash fire had been extinguished. Further inspection of the left engine found that the alternate air valve was in the closed position and that the spark plugs exhibited black, sooty deposits.
Additional Information
The aircraft was equipped with some deice and anti-ice protection. However, according to the airplane manufacturer and a Federal Aviation Administration (FAA) inspector, the accident airplane and three other similar airplanes operated by the same operator were not certified for flight into known icing conditions. Additionally, none of the four airplanes met the requirements specified in Federal Aviation Regulation (FAR) 135.227(c).