ANC25LA025

The pilot, who was also the owner of the airplane, was conducting a familiarization flight with the pilot-rated passenger, who was a prospective buyer of the airplane. The pilot reported having flown the airplane for a total of 35 hours after the engine had been removed, disassembled, and reinstalled just over 3 years before the accident; however, the airframe and engine logbooks show no hours accrued since the engine reinstallation. The pilot reported that, during engine run-up, the engine speed did not decrease when he pulled the carburetor heat knob. He stated that, after he shut down the engine, he “had the pilot actuate the carb heat push/pull knob several times while I observed and felt the mechanism on the air box move in a way that seemed normal.” The pilot then elected to continue the flight. During the initial climb out, the pilot pulled the carburetor heat knob to recheck the functionality of the carburetor heat and immediately experienced a large drop in engine speed. He kept the carburetor heat on, “expecting it to clear quickly if it was ice, as it has always done in the past.” After observing that power was not being restored, he turned back toward the airport. The engine continued to run at low power; however, the airplane was unable to maintain altitude and the pilot elected to land on a frozen river south of the airport. During the landing, the airplane nosed over, which resulted in substantial damage to the wings. Postaccident examination of the engine revealed that the carburetor heat cable was too long, had a visible kink where it attached to the heat control mechanism, and did not properly engage the heat control mechanism in either the fully open or closed position. Due to the excessive length of the carburetor heat control cable, the carburetor heat was always partially on, and this condition could not be changed when actuated by the control knob in the cockpit. The excessive cable length most likely occurred due to inadvertent repositioning of the clamp attaching the carburetor heat control cable sheath to the carburetor airbox during a previous engine removal and reinstall about three and a half years before the accident flight. The environmental conditions at the time of the accident were not conducive to the accumulation of carburetor icing. The carburetor heat control cable’s excessive length and incorrect positioning likely prevented the proper operation of the carburetor heat, resulting in a partial application of carburetor heat and partial loss of engine power during climb out.

On March 16, 2025, about 1415 Alaska daylight time, a Cessna 172A airplane, N7274T, was substantially damaged when it was involved in an accident near Fairbanks, Alaska. The pilot reported minor injuries, and the pilot-rated passenger was uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot, who was also the owner of the airplane, was conducting a familiarization flight with the pilot-rated passenger, who was a prospective buyer of the airplane. The pilot reported that, during engine run-up, the engine speed did not decrease when he pulled the carburetor heat knob. He stated that, after he shut down the engine, he “had the pilot actuate the carb heat push/pull knob several times while I observed and felt the mechanism on the air box move in a way that seemed normal.” The pilot then elected to continue the flight. During the initial climb out, the pilot pulled the carburetor heat knob to recheck the functionality of the carburetor heat and immediately experienced a large decrease in engine speed. He kept the carburetor heat on, “expecting it to clear quickly if it was ice, as it has always done in the past.” After observing that power was not restored, he turned back towards the airport. The engine continued to run at low power; however, the airplane was unable to maintain altitude and the pilot elected to land on a frozen river south of the airport. During the landing, the airplane nosed over, which resulted in substantial damage to the wings. Postaccident examination of the engine revealed that the carburetor heat cable did not provide the required travel to properly engage the carburetor heat control mechanism in either the fully open or closed position. Additionally, the carburetor heat was found to be difficult to operate from the cockpit of the airplane, requiring an excessive amount of force to move the control mechanism in either direction. The result was that the carburetor heat was always partially on, and this condition could not be changed when actuated by the control knob in the cockpit. A visible kink in the carburetor heat control cable was observed where it attached to the carburetor heat control mechanism. The clamp that attached the carburetor heat control cable sheath to the carburetor airbox appeared to be installed in the wrong position, about 180° from the position indicated in the Cessna 172 & 175 Parts Catalog (1956-1962). Review of the airplane’s maintenance logs indicated that no flight hours had been logged since 2021. The pilot reported having flown the airplane for a total of 35 hours after the engine had been removed, disassembled, and reinstalled just over 3 years before the accident; however, the airframe and engine logbooks show no hours accrued since the engine reinstallation. In November 2021, the engine had been removed, disassembled, and reinstalled “due to [the] engine running without oil.” The temperature at the time of the accident was -12°C(10°F) with a dewpoint of 18°C (0°F). A review of the carburetor icing probability chart in FAA Special Airworthiness Information Bulletin CE-09-35 indicated that the conditions at the time of the accident were not conducive to the accumulation of carburetor icing.