CEN23LA206

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.

On May 29, 2023, about 1130 mountain daylight time, a Cessna 172B airplane, N8098X, was substantially damaged when it was involved in an accident near Divide, Colorado. The pilot and passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that the local flight to Antero Reservoir proceeded normally after departing from Meadow Lake (FLY), Colorado Springs, Colorado. On the return leg back to FLY at 10,000 ft msl, the pilot heard a loud sudden noise and the engine immediately lost partial power. The engine rpm during the cruise flight up to the time of the partial power loss had remained steady at about 2,400 rpm with normal oil pressure according to the pilot. The pilot attempted to troubleshoot the power loss by adjusting the engine throttle setting, testing both magnetos, and applying the carburetor heat. His actions were unsuccessful at providing any substantial power increase. The pilot elected to perform a forced landing. After touchdown in a large grassy area, 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 the fuselage. The wreckage remained inverted in the field until it was recovered about three weeks after the accident. An examination of the wreckage was performed at the owner’s residence on August 3, 2023. Both wings were removed during recovery and contained no fuel in either fuel tank during the examination. The wing fuel tank caps were both found in their locked position with intact gaskets. The pilot reported that 25 gallons of fuel were onboard at the time of departure. The fuselage fuel system was examined with no blockages observed. Less than a pint of fuel from the fuselage fuel lines was recovered at the engine firewall. The gascolator was examined and found to still contain fuel. The collected fuel from the fuel lines and gascolator was blue in color with a smell consistent with 100LL Avgas. The fuel was tested for possible water contamination with no water being found in the collected fuel. The fuel screen was also removed and found to be clear of debris. The fuel selector valve was found in the BOTH position and rotated correctly when moved by hand. The engine remained attached to the engine mount and the throttle and carburetor heat cables were found attached to the carburetor and airbox respectively. The mixture cable was found separated from the carburetor with damage consistent with impact. The carburetor heat was tested by hand with normal operation of the door in the airbox. The ignition system was tested by manually rotating the propeller with the ignition key on both and spark was observed on all spark plug leads. The carburetor was removed from the intake system with no blockages observed in the venturi, around the throttle plate, fuel inlet ports, or fuel nozzle. The throttle plate had freeand smooth movement through the entire allowed range. The bowl and floats were removed with no fuel observed in the bowl and the bowl was clear of any foreign material. The air intake and exhaust system were inspected with a borescope with no blockages or issues observed. The Brackett engine filter was intact and clean The Cessna 172B Owner’s Manual and Airworthiness Directive 72-07-02 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. The Cessna Owner’s Manual further states that should power irregularities occur due to fuel vapor during operation on both tanks the pilot is to switch to a single tank for a period of 60 seconds and then switch to the opposite tank to restore engine power. It was stated by the pilot that he verified the fuel selector was still in the “BOTH” position during his troubleshooting.