ERA25LA127 · Cessna 172 P

During a solo cross-country flight, the student pilot initiated a cruise-power descent from about 2,300 ft and about 2300 rpm (about 65% engine power). He reported that, when the airplane was about 1,500 ft, it felt like the engine was “pulled to idle.” He stated that he manipulated the throttle control, but the engine did not respond. He confirmed that the mixture control was set to full rich, the fuel selector was in the Both position, and the primer was locked. He said he then applied carburetor heat, which had “no effect,” then he removed carburetor heat and looked for a place to land the airplane. The student pilot selected a road for a forced landing, and the airplane’s right wing impacted trees about 10 ft above the surface and the airplane continued striking trees after ground contact. The airplane came to rest upright on its nose against trees on the side of a two-lane road. An odor of fuel was present at the site, but the contents of the fuel tanks could not be established due to the airplane’s position. Examination of the airframe and engine found no abnormality that would have prevented normal operation. A serviceable propeller was installed, and an engine start was initiated on a test stand. The engine started immediately, then idled, accelerated, and ran smoothly at full power for several minutes without interruption and no anomaly noted. A magneto check was performed with no anomaly noted, and oil indicated pressures were in the normal range. Engine power was reduced to idle, where the engine ran smoothly without interruption. A magneto grounding check was normal, and a slight rpm rise was heard when the mixture was pulled to idle cutoff. The engine was stopped with the mixture placed at the idle cutoff position. A post-run inspection of the engine revealed no leaks and no abnormality. The atmospheric conditions near the accident site around the time of the accident were conducive to the formation of carburetor icing at glide and cruise power settings. Given the atmospheric conditions and the lack of mechanical anomalies found during postaccident examination and an engine test run, the engine likely lost power due to the accumulation of carburetor icing during the en route descent. Although the student pilot’s subsequent brief (rather than sustained) application of carburetor heat was inconsistent with the emergency procedures for responding to a loss of engine power, this likely did not affect the outcome of the flight. Given the airplane’s low altitude when the student first perceived the engine power anomaly, it is unlikely that carburetor heat applied in response could have cleared the ice and restored engine power in time to prevent the forced landing.

Verbatim NTSB analysis and probable cause from the NTSB dataset