Incident Overview
A pilot reported that while conducting an instrument approach in heavy rain, there was a partial loss of engine power. The pilot applied carburetor heat, but the engine still did not provide full power. Despite the power issue, the pilot continued the VOR/DME approach.
Approach and Landing
Upon sighting the runway, the pilot determined that the aircraft was too high to land. The pilot then entered a downwind leg and landed with full flaps on Runway 32. The pilot stated that the aircraft was too fast, and after touchdown, the aircraft began hydroplaning. Subsequently, the aircraft continued off the end of the runway, struck a ditch, and nosed over.
Decision Against Go-Around
The pilot reported that he decided not to execute a go-around because he considered the engine unreliable and noted high obstructions off the end of the runway.
Weather Conditions
The pilot reported the wind as from 070 degrees at 6 knots. Approximately 55 miles east at Rolla, Missouri, the weather at 1148 CDT was: 600 scattered, 6000 overcast, visibility 5 miles with fog, wind 160 degrees at 10 knots, temperature 64 degrees Fahrenheit, dew point 62 degrees Fahrenheit.
Carburetor Icing Information
According to icing probability charts, serious carburetor icing could be encountered at cruise power with float-type carburetors.