NTSB Factual Report

On July 18, 2014, about 1541 central standard time, a Stinson 108-1 single engine float equipped airplane, N9034K, registered to Mimus Aero LLC, Minneapolis, Minnesota, and operated by a private individual, was substantially damaged during a forced landing after a loss of engine power near Bruno, Minnesota. The private pilot was not injured. The personal cross country flight was being conducted under the provisions of Federal Code of Regulations Part 91. A flight plan was not filed and visual meteorological condition prevailed throughout the area. The flight originated from the Sky Harbor Airport (DYT), Duluth, Minnesota, about 1510, and was enroute to the Surfside Seaplane Base (BY4), Lino Lakes, Minnesota, when the accident occurred.

According to the pilot, about 30 minutes after departing DYT, at an altitude on 2,000 AGL, the engine sputtered for about 10 seconds and then lost all power. The pilot initiated emergency procedures for a restart and located an off airport landing site while in an emergency descent. The airplane touched down on its floats in a grassy field and sustained substantial damage to the fuselage. The pilot exited the airplane with no injuries.

FAA inspection of the airplane on scene revealed bucking damage of the fuselage just aft of the right cabin door and additional fuselage buckling near the left aft attachment point of the floats. Both float attachment struts were found broken. There was marks found on the aft face of the propeller blades consistent with contact of the walk wire between the floats. The airplane was found resting in a slight right wing low attitude and fuel flowed freely from the engine fuel sump. Fuel was drained from both tanks and the fuel strainer (7 gallons in the left tank and 21 gallons in the right tank). All of the fuel appeared to be clean, not contaminated, and had the appearance of 100LL aviation fuel. The fuel selector valve was in the right tank position and appeared to operate properly within its detents. The top spark plugs were removed and the engine rotated by hand with the propeller in the normal rotation direction. All 6 cylinders appeared to have good compression. Both magneto impulse couplings appeared to snap normally while rotating the engine. All of the spark plugs appeared to be in good condition. The airplane was found resting in a slight right wing low attitude and fuel flowed freely from the engine fuel sump. No obvious anomalies were found with the engine on scene.

After the airplane wreckage was recovered, maintenance personnel were able to start and run the engine with an external fual supply. The engine started and ran for about 30 seconds and then stopped. After the run attempt, the fuel gascolator and carburetor intake screen were removed and cleaned. No significant debris was found. A small amount of debris was found in the carburetor fuel bowl. After inspecting the remainder of the engine, the engine was started again, ran for about 1 minute, and stopped again. A replacement carburetor was then installed. The engine was started and ran normally with the replacement carburetor.

NTSB Probable Cause

The total loss of engine power due to an anomaly with the carburetor system that could not be determined during postaccident examination.