NTSB Factual Report

On April 18, 2015, about 1748 central daylight time, an experimental, amateur-built Pitts model 12 airplane, N12DR, was substantially damaged during a forced landing near Falconhead Airport (37K), Burneyville, Oklahoma. The commercial pilot sustained minor injuries. The airplane was registered to and operated by the pilot under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91 as a personal flight. Day visual meteorological conditions prevailed, and no flight plan was filed for the local flight that departed about 1740.

The pilot reported that after a short local flight he reentered the traffic pattern on the downwind leg to practice landings on runway 18 at 37K. The pilot stated that after entering the downwind leg he made an initial reduction of engine power to 22 inches-of-manifold pressure and 2,000 rpm and that the airplane decelerated to 100 mph. He subsequently made another engine power reduction to about 15 inches-of-manifold pressure at 2,000 rpm when the airplane was abeam the approach end of runway 18. During the base leg he determined that the airplane would require additional engine power to land at his preferred touchdown point on the runway; however, the engine did not respond when he advanced the throttle. He subsequently increased both the throttle and propeller controls with no noticeable change in engine power. The pilot reported that the airplane did not have enough altitude to reach the runway, so he made a left 90° turn from the final approach toward an open wheat field for a forced landing. He stated that the airplane came to rest nose down after both main landing gear collapsed upon landing in soft muddy terrain. The forward fuselage, engine mounts, and both lower wings were substantially damaged during the accident.

A postaccident examination established that the main fuel tank was leaking from a broken fuel line, but the tank still contained ample fuel (about 3/4 full). Throttle and mixture control cable continuity was confirmed from the cockpit to their respective engine components; however, the controls did not move due to impact-related damage. Flight control cable continuity was established from each flight control surface to its respective cockpit control. Both main landing gear had collapsed aft during impact. The engine remained partially attached to the firewall through several damaged mounts. Internal engine and valve train continuity were confirmed as the crankshaft was rotated. Except for cylinder no. 5, compression and suction were noted on all cylinders in conjunction with crankshaft rotation. A borescope inspection of the no. 5 cylinder did not reveal any anomalies and confirmed piston and valves movement in conjunction with crankshaft rotation. The lack of compression on cylinder no. 5 was attributed to a stuck ring and not to a mechanical failure. The forward spark plugs were removed and exhibited features consistent with normal engine operation. A functional test of the fuel selector revealed no anomalies. There was no evidence of a vent restriction to the main tank when compressed air was blown into the fuel system vent line. There were no restrictions noted with the vapor return line between the main tank and the bubbler, and the correct restricted orifice was installed in the line. The fuel system exhibited impact-related damage of several fuel lines and their associated fittings. The main fuel line contained an unmeasured amount of water and there was a white paste-like material inside the line fitting. The fuel drain for the header tank separated during impact, and about 1 teaspoon of water was recovered from the header tank. About 3 tablespoons of uncontaminated fuel was recovered from the throttle body inlet and about 6 fluid ounces of uncontaminated fuel was drained from the bubbler assembly. The fuel system did not have a gascolator installed; however, the airplane was equipped with a 62 micron inline fuel filter. A visual inspection of the fuel filter revealed trace amounts of aluminum shavings, water, cellophane tape, and organic material. There was white Teflon paste observed on the inlet threads to the electric fuel pump. No anomalies were noted with the electric fuel pump during a functional test. The mechanical fuel pump was removed and provided fuel flow during a bench test. There was mud found impacted in the fuel controller assembly that was attributed to impact. The fuel controller reference line fitting was found finger tight. Examination of the fuel injection nozzle did not reveal any evidence of water contamination on the interior nozzle passages; however, the fuel disk revealed trace mud deposits that were attributed to impact.

NTSB Probable Cause

The partial loss of engine power due to contamination of the fuel system.