ERA15LA318 · Cessna 172K

The private pilot was conducting a personal cross-country flight. The pilot indicated that, after takeoff, he climbed the airplane to 5,000 ft mean sea level and then leveled it off. About 10 to 15 seconds later and with the engine operating at 2,500 rpm, the fuel selector positioned to "both," and the fuel-to-air ratio leaned, he noticed a vibration and decreased engine performance. He immediately turned to a forced landing area and, while descending, conducted emergency procedures, which included applying carburetor heat (which remained on during the descent), checking the magnetos, and switching the fuel selector to the left and right positions. These attempts to restore full engine power were unsuccessful. He maneuvered the airplane for a forced landing in a field, and, after touchdown, the nose landing gear broke off, and the airplane nosed over.

Examination of the airplane at the accident site revealed that a sufficient quantity of fuel remained in both fuel tanks; no fuel contamination was noted in the fuel strainer or carburetor bowl. Postaccident examination of the engine revealed no evidence of any mechanical malfunctions or failures that would have precluded normal operation. The engine was started and operated to near full-rated rpm, or about the same rpm the pilot reported existed when the partial loss of power occurred, and no discrepancies were noted.

Although the reported weather conditions at the time of the accident at the approximate altitude where the power loss occurred were conducive to the accumulation of carburetor icing at glide power, the pilot reported that he applied carburetor heat while troubleshooting the loss of engine power, which would have melted any ice, but full engine power was not restored. Further, he was operating at a higher power setting than glide power; therefore, the investigation was unable to determine the cause of the partial loss of engine power during cruise flight.

Verbatim NTSB analysis and probable cause from the NTSB dataset