Cessna 172M N12805 accident near Clearbrook, Minnesota

Probable cause

The pilot’s delayed use of carburetor heat which resulted in the loss of engine power due to carburetor icing.

NTSB analysis

The pilot reported that he had just been cleared to fly the GPS approach in night instrument meteorological conditions when the engine rpm decreased. The pilot turned on the carburetor heat, enrichened the fuel mixture, and advanced the throttle forward in order to troubleshoot the loss of engine power; however, there was no change in the engine operations.

The pilot did not recall the accident sequence. Security video footage showed that the airplane touched down on the top of a one-story building, then impacted a retaining wall and the ground. The airplane sustained substantial damage to the engine mounts and forward fuselage.

A postaccident examination of the engine revealed no mechanical anomalies that would have precluded normal operation. The investigators determined that there should have been adequate fuel to complete the flight. The temperature was about 37° F and the dew point was about 35° F. According to the carburetor icing probability graph conditions were conducive for serious icing at cruise power.

The loss of engine power was likely due to the accumulation of carburetor icing during the flight. While the pilot did activate the carburetor heat, it is likely that the ice had already accumulated to a point that the carburetor heat was insufficient to melt the ice and restore full engine power.

Text from the NTSB. Open the NTSB docket for CEN24LA168 for the full record.