On July 26, 2000, at 1750 central daylight time, a Bohner Pitts Model 12, N811WS, piloted by an airline transport pilot, sustained substantial damage on impact with terrain and objects during a forced landing to a field following an in flight loss of engine power near Neosho, Missouri. The purpose of the flight was that airplane's flight test. The flight was operating under 14 CFR Part 91. Visual meteorological conditions prevailed during the flight. No flight plan was on file. The pilot and passenger sustained minor injuries. The local flight originated from Neosho-Hugh Robinson Airport, near Neosho, Missouri, at 1700 and was maneuvering in the traffic pattern at the time of the accident.

The pilot stated, "Second flight on N811WS checking systems, flight controls, [and] controls in front cockpit all OK. (first flight day before - all went well-) After TO/climbed to 7000 ft. for flight check-steep turns, stall power off-54mph, stall power on approx 50mph, both stalls very light, straight ahead very little rudder, slow flight approx 80mph, after 45min we returned to the airport (EOS) power on decent to the traffic pattern approx 800 ft agl, 180mph straight [and] level no trim problems starting the left cross wind turn[.] I add a small amount of power when the engine quit, a large bang, not mechanical but carbaroter [carburetor] or fuel related, like a backfire, and no power - the engine poped several times. I changed the throttle settings several times, turned on the fuel boost pump [and] the fuel injector. No help. Turned to the right to a hay field, tried to miss the 2,000 lb hay rolls, no place to land-jumped the fence at the end-came down on the tailwheel first then on the main gear-got the prop first on the ground, then hit the hay roll. Hit the right side of engine and right wings. The aircraft nosed over and slid on the engine for approx 20ft. then over on its back. The field was flat with 2 fences across it. No place to land inbetween hay rolls."

A Federal Aviation Administration (FAA) inspector examined the airplane wreckage. He stated, "Several spark plugs were pulled, marked and examined visually. There was no sign of over heating on the spark plugs that were removed. Some spark plugs were gapped different than others as noted in the pictures. ... The engine compression check was found to be satisfactory. ... Ignition was not checked."

The photographic film taken during the examination was developed and reviewed. The photographed spark plugs exhibited a dark black color. See appended photographs.

At 1753, the Joplin Regional Airport, near Joplin, Missouri, weather was: Wind 160 degrees at 8 knots; visibility 10 statute miles; sky condition clear; temperature 31 degrees C; dew point 21 degrees C; altimeter 29.99 inches of mercury.

A copy of a Transport Canada Carburetor Icing chart was reviewed. The temperature and dew point were plotted on the icing chart and their intersection is located in the serious icing-descent power range.

On an additional statement, the pilot stated, "I found out after the fact that the engine has a tendency to flood out. Run too rich on fuel. The accelerator pump, pumps too much fuel. The FAA looked at the engine and said that there was fuel in the carburetor and black residue in the cylinders. Too much fuel. There is a carburetor mod for the engine which we put on the next a/c we built and it, the engine, Vedeneyev M14PF, has ran without any problems now for 40 hrs. Conclusions: The engines and carburetors need to be checked and tuned for our fuels here in the US. Check for the carburetor mods that are out there and talk to someone who has one and is flying one now to learn its secrets."

The airplane's operation limitations, as issued by the FAA, stated, "During the flight testing phase, no person may be carried in this aircraft during flight unless that person is essential to the purpose of the flight test."

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