Amateur-built ULTRA-PUP N3073X accident near Lyman, Maine

Probable cause

The accumulation of ice in the automotive engine’s carburetor, which resulted in a loss of engine power.

NTSB analysis

About 20 minutes into the cross-country flight, the pilot of the experimental amateur-built airplane detected a vibration of the airplane’s engine that “didn’t sound good,” and noticed a drop in the rpm of the automotive-conversion engine. He immediately applied carburetor heat, but the engine continued to lose power until the airplane could no longer maintain altitude and began to descend from its cruise altitude of 1,500 feet above ground level. The pilot performed a forced landing into the trees below, substantially damaging the airplane’s fuselage, wings, and empennage. Postaccident examination of the airplane, its engine, and its fuel system revealed no evidence of preimpact malfunctions or anomalies that would have precluded normal operation. Although the fuel system was compromised by impact damage, the fuel that remained in the system was absent of contamination. According to a carburetor icing probability chart published by the Federal Aviation Administration, the temperature and dew point reported at an airport located about 6 nautical miles from the accident site were conducive to “serious icing at cruise power.”

Text from the NTSB. Open the NTSB docket for ERA13CA010 for the full record.