ERA17LA202 · Cessna 172P

Following an uneventful preflight inspection of the airplane, the student pilot and the flight instructor taxied and then began their runup checks of the engine. The flight instructor stated that during the runup he noted a “normal” drop in engine rpm when they tested the carburetor heat, both with power on the engine and with the throttle pulled back to idle. The subsequent takeoff takeoff was normal, but at about 350 ft above the ground, the flight instructor heard a slight decrease in engine power; he asked the student pilot if he was guarding the throttle, and he responded that he was. The power then came back. Then, at about 400 ft above the ground, the engine lost power again. The flight instructor stated that this time it was significant, as it dropped to 1,900 rpm and was fluctuating. The flight instructor then took the controls of the airplane, after which the power dropped to 1,100 rpm and continued to fluctuate. There was no available runway remaining and the airplane was losing altitude, so the flight instructor landed the airplane in a grass field on the airport property. He stated that on touchdown, he had very poor braking capability (likely due to the wet grass). The airplane struck a tree with the left wing, then struck the airport fence and substantially damaged the airplane’s wings. Postaccident examination of the airplane revealed an adequate supply of uncontaminated fuel. Test runs of the engine were performed, during which the engine ran without hesitation and displayed no evidence of preimpact failures or malfunctions that would have precluded normal operation. Review of a carburetor icing probability chart revealed that the atmospheric conditions at the time of the accident were conducive to the formation of carburetor ice. Given this information, it is likely that while operating the airplane on the ground prior to takeoff, a period during which the engine would typically be operating at low power, carburetor ice began forming, which continued until the engine began losing engine power during the initial climb.

Verbatim NTSB analysis and probable cause from the NTSB dataset