ANC96LA069

The pilot was in cruise flight on a personal flight when he noted a rise in the rear cylinder head temperature of the number two (rear) cylinder. He adjusted the mixture screw and watched the temperature continue to rise. During a precautionary landing, the engine stopped producing power, and the pilot was forced to land the airplane on a road. Subsequent examination showed that the piston in the rear cylinder would not move. Examination of the mixture screws showed that the mixture screw controlling the rear cylinder was in the lean position. The direction on rotation for leaning or enriching the mixture was not marked on the mixture screws.

On May 5, 1996, at 0930 Alaska daylight time, a wheel equipped Challenger 2, experimental airplane, N1591G, registered to and operated by the pilot, experienced an engine stoppage and subsequent forced landing near Talkeetna, Alaska. The personal flight, operating under 14 CFR Part 91, departed Talkeetna and the destination was Birchwood, Alaska. No flight plan was filed and visual meteorological conditions prevailed. The certificated private pilot, the sole occupant, was not injured and the airplane received substantial damage.

During a telephone conversation with the pilot on May 5, 1996, he stated that during cruise flight he noticed a rise in the rear cylinder head temperature of the two cylinder, two cycle engine. He adjusted the individual mixture screw and watched the cylinder head temperature continue to rise. He selected the Talkeetna Spur Road as a precautionary landing area. As he was aligning the airplane for a landing, the engine stopped producing power and he was forced to land on the road. During the landing roll on the roadway, a truck was approaching from the opposite direction. The pilot stated the truck was not slowing down so he guided the airplane as far to the right side of the road as possible. The right main landing gear rolled into soft sand and the airplane veered off the roadway into cut alder bushes. The right main and nose landing gear separated from the airplane.

Subsequent examination of the airplane showed that each cylinder had an individual mixture screw which consisted of a long shaft mounted overhead in the cockpit. Examination of the mixture screws showed that the number two cylinder mixture screw was turned to a lean mixture setting. Examination of the number two cylinder showed that the piston had seized moving in the cylinder.

The mixture screw shafts were labeled according to their corresponding cylinders. However, the direction needed to turn the mixture shaft to enrich or lean the mixture was not marked.