Cessna 172D N2320U accident near Shenandoah, Texas

Probable cause

The pilot's delayed application of carburetor heat, which resulted in the total loss of engine power due to carburetor icing during cruise flight.

NTSB analysis

The private pilot reported that he was conducting a personal flight when the engine began to "sputter and lose power" during cruise flight. He was unable to restore full engine power after applying carburetor heat, selecting a full-rich mixture setting, and verifying that the selector valve was positioned to draw fuel from both tanks. The engine subsequently lost total power, and the pilot made a forced landing to a nearby vacant parking lot. The pilot was unable to stop the airplane during the landing roll before it impacted a concrete curb and nosed over.

Postaccident engine examination did not reveal any evidence of preimpact anomalies that would have precluded normal operation. The pilot had topped off the airplane's fuel tanks before departing on the 1-hour flight; the airplane had a fuel endurance of 4.2 hours when the tanks were full. Although the fuel quantity was not measured after the accident, the airplane likely had at least 3 hours of fuel remaining at the time of the accident. The pilot stated that fuel samples drained from each wing fuel tank during his preflight inspection were consistent with 100 low-lead aviation fuel and were not contaminated with water or debris. Additionally, postaccident testing of the fuel source used to refuel the airplane before the flight did not reveal any evidence of water or debris.

The weather conditions at the time of the accident were conducive to the formation of carburetor icing at glide and cruise power settings. Based on the available information, it is likely that the engine initially lost power after developing carburetor ice and that the application of carburetor heat was ineffective and possibly exacerbated the problem by introducing less-dense hot air, which likely led to a further drop in rpm. Additionally, the pilot's delay in applying carburetor heat until after the engine began running roughly likely resulted in insufficient exhaust gas temperature to produce hot air in the exhaust muffler, which rendered the use of carburetor heat ineffective at melting the accumulated ice.

Text from the NTSB. Open the NTSB docket for CEN15LA292 for the full record.