Costruzioni Aeronautiche Tecna P2006T N968GV accident near Larkspur, Colorado

Probable cause

The flight instructor’s failure to apply carburetor heat, which resulted in a loss of left engine power due to carburetor icing.

NTSB analysis

The flight instructor and commercial pilot receiving multi-engine instruction intentionally shut down the left engine after they performed one-engine-inoperative (OEI) training. They restarted the left engine successfully on the second attempt and proceeded back to the departure airport. During the descent, the pilots noticed that the airplane required additional right rudder to maintain control and then noticed a decrease in left engine coolant temperature and rpm. Carburetor heat was not used during the flight. Due to the partial loss of engine power, they diverted to the nearest airport for a precautionary landing. During the descent for landing, they secured the left engine and feathered the propeller. They were unable attain the runway and landed on a highway; when the airplane touched down, it struck a road sign with the left wing. The flight instructor then pitched up to avoid vehicles and veered left into a marshy area next to the highway.

Postaccident examination of the airplane revealed that the carburetor heat levers remained in the OFF position. The left propeller lever was found retarded, but not in the feathered position. Examination of the airplane and functional test runs of both engines did not reveal any preimpact mechanical malfunctions or failures that would have precluded normal operation.

The airplane was operating in atmospheric conditions that were conducive to the formation of serious icing at glide power settings.

Text from the NTSB. Open the NTSB docket for CEN24LA226 for the full record.