CHI96LA203

The aerial application flight experienced a gradual power loss during its initial climbout from takeoff. The pilot landed in a field with a soft surface. The airplane nosed over upon touchdown. Examination of the airplane's engine revealed no mechanical aniomalies that would prevent the prodiuction of normal power. The pilot said he had fueled the airplane and checked for water in the fuel before takeoff. He said he had not encountered carburetor ice during previous takeoffs earlier in the day. The pilot said the engine had hesitated on takeoff during the past 2 to 3 weeks. He said it did this on a random basis. The pilot said the airplane's engine had been idling about 5 minutes before takeoff. He said he did not apply carburetor heat when he noticed the power loss. According to an FAA carburetor icing probability chart, the temperature/dew point at the accident site posed a serious threat for carburetor icing at low power settings.

On June 15, 1996, at 1745 central daylight time (cdt), a Schweizer G164B, N36311, piloted by a commercial pilot, was substantially damaged when it nosed over during a forced landing. The 14 CFR Part 137 flight was not operating on a flight plan. Visual meteorological conditions prevailed at the time of the accident. The pilot was not injured. The flight departed a private airport near Oslo, Minnesota, at 1745 cdt.

During an interview with the pilot he said the engine gradually lost power while the airplane was on its initial climb after takeoff. He said he landed on a rain softened field and the airplane nosed over shortly after touchdown. The pilot said the engine had hesitated during acceleration on takeoffs during the past 2 to 3 weeks. He said the hesitation occurances were random.

The pilot said he had refueled the airplane and checked the fuel for water before takeoff. He said he did not observe any water or debris in the fuel during the sampling process. He said the power loss was not like it was induced by carburetor ice. The pilot said he had not encountered carburetor icing on earlier flights during the afternoon. The pilot said atmospheric conditions were favorable for carburetor ice formation.

The Federal Aviation Administration Principal Avionics Inspector (PAI) representing the NTSB on-scene said he asked the pilot if he had used carburetor heat when he noticed the power loss. The PAI said the pilot told him he did not use the carburetor heat. The PAI said the pilot told him he had been idling the engine on the ground for about 5 minutes before takeoff.

The engine's sparkplug electrodes were tan/gray in color. During the engine examination the supercharger impeller could be moved about 10 to 20 degrees along its rotational axis. Further examination revealed the super-charger drive gears were not damaged. The super-charger seal was not damaged. The carburetors float chambers were crushed inward. Both floats were crushed inward about 1/4-inch and pushed against the chamber's walls. Both floats were checked for fuel and pre-impact leaks. The results of the examination were negative. The needle valve seat and carburetor finger screen were clean. Both magnetos produced spark when turned by hand.

The temperature/dewpoint at the accident site was 85 and 60 degrees Fahrenheit respectively. Accoridng to the Federal Aviation Aministration's carburetor icing probability chart, these conditions posed a seriuous icing condition for an engine operating at glide power.