Cessna 172 - H N8282L accident near Circleville, Texas

Probable cause

The failure of the engine to regain normal power after a simulated engine failure due to carburetor icing, which resulted in a forced landing on muddy terrain and a subsequent nose-over.

NTSB analysis

The flight instructor was conducting an instructional flight with a student pilot. The student reported that the preflight engine run-up was normal and that, before takeoff for the flight, there was a small wait because they were the fourth airplane in line for takeoff. At takeoff, the engine power was not normal, but leaning the mixture returned the engine performance to normal. After performing several flight maneuvers at 4,500 ft mean sea level (msl), the flight instructor simulated an engine failure by applying carburetor heat and retarding the throttle to idle. After descending the airplane to 2,500 ft msl, the flight instructor attempted to clear the engine and pushed the throttle control to full power, but the engine power was not restored. Subsequent attempts to restart the engine were unsuccessful, and the student then transferred the flight controls to the flight instructor, who then conducted a forced landing to muddy terrain, which resulted in the airplane nosing over.

The weather conditions at the time of the accident were conductive to moderate carburetor icing at cruise power and serious carburetor icing at descent power. Given the delayed takeoff, during which the engine would have been at an idle power setting, and that the mixture needed to be leaned at higher engine power to return to normal, it is likely that carburetor icing had accumulated. Although the flight instructor applied carburetor heat for the simulated engine failure to prevent carburetor icing, there would have been reduced heat output by the engine at the idle power setting, which would not have been effective in preventing carburetor icing.

Text from the NTSB. Open the NTSB docket for CEN15LA215 for the full record.