Amateur-built MAC CUB N669WH accident near Ogden, Utah

Probable cause

The pilot’s failure to use carburetor heat during the flight, which resulted in a partial loss of engine power due to carburetor icing.

NTSB analysis

The pilot and pilot rated passenger were conducting a local flight when the engine began to run roughly, and partial loss of engine power followed. The airplane was unable to maintain altitude, and the pilot made a forced landing onto a muddy road. During the landing roll, the airplane sunk in the mud, nosed over, and came to rest inverted, causing substantial damage to the left wing and vertical stabilizer. An engine examination and test run were performed, which revealed no preaccident mechanical failures or malfunctions that would have precluded normal operation.

The nearest weather reporting facility, located about 6 nautical miles from the accident site, reported a temperature of 35.6oF and a dew point of 19.4oF, which was in the range of atmosphere conditions that are conducive to carburetor icing at glide and cruise power settings. The pilot reported that the carburetor heat was not activated at the time of the partial loss of engine power.

The pilot also reported that he was in the rear airplane seat. Although the pilot had access to both sets of flight controls, the rear seat compartment was not equipped with a carburetor heat control handle. Engine power would likely have been restored if the carburetor heat had been engaged.

Text from the NTSB. Open the NTSB docket for WPR18LA102 for the full record.