CEN23LA206 · Cessna 172B

While en route at 10,000 ft mean sea level (msl), the pilot reported that the engine made a sudden noise with an associated partial loss of power. The pilot adjusted the engine throttle position, tested both magnetos, and applied carburetor heat with no significant engine power increase. He elected to conduct an off-field landing into grassy terrain. After touchdown, the airplane encountered rough terrain and the nose landing gear collapsed. The airplane nosed over and came to rest inverted, which resulted in substantial damage to both wings and fuselage. An examination of the wreckage revealed no evidence of a fuel system malfunction or anomaly. The wing fuel tanks remained intact. All fuel lines and screens were unobstructed, the fuel selector operated normally, and the recovered fuel was tested for possible water contamination; no water was found in the fuel system. The only fuel recovered was located in the gascolator fuel line and gascolator; however, the airplane remained inverted at the accident site for several weeks after the accident and the amount of fuel onboard at the time of the accident could not be determined. Postaccident examination of the engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The pilot reported that he verified the fuel selector was in the BOTH tank position during cruise and engine troubleshooting. The airplane owner’s manual and a Federal Aviation Administration airworthiness directive both state that the fuel selector be switched to single tank operation upon reaching cruise altitudes above 5,000 ft due to fuel vapor formation in the fuel lines above 5,000 ft. However, due to lack of fuel quantity information at the time of the accident whether vapor lock contributed to the loss of engine power could not be determined.

Verbatim NTSB analysis and probable cause from the NTSB dataset