20010107000099A

(-23) Pilot was descending after releasing jumpers, when he tried to level off he found that he had no throttle. Pilot looked for a field and landed, when he did the nose wheel touched down it dug in and the a/c flipped over.(.4) the flight departed with approximately 20 gallons of fuel in each fuel tank and offloaded skydivers at 10,500 feet, then descended to return with the throttle at idle, the fuel/air ratio leaned; and carburetor heat applied. At 2,000 feet, the pilot began to level off and, "realized I was having engine trouble and began my emergency procedures for an engine failure at altitude...." He checked the position of the fuel selector valve which was in the same position it was selected for takeoff, "both on." He positioned the fuel selector to the left, right, and both positions with negative results, and also checked "my ignition and check all fuses." He was unable to start the engine and performed a forced landing in a field. Before touchdown he turned off the fuel selector valve; after touchdown, the airplane nosed over. The fuel strainer was empty when examined by a mechanic approximately 45 minutes after the accident. Examination of the airplane by an FAA inspector approximately 24 hours after the accident revealed the flexible hose from the fuel strainer to the carburetor contained a slight amount of fuel (capful). No discrepancies with the fuel strainer, ignition, or vent systems noted. Following release by the FAA for recovery, the carburetor was removed and no fuel spray noted from the accelerator pump discharge nozzle when the throttle was activated. The fuel flow rate through the fuel selector valve was less with the fuel selector valve positioned to the right tank than with the valve positioned to the left or both positions. Disassembly of the fuel selector valve revealed no evidence of debris or wear; no determination was made as to the reason for the low fuel flow rate with the fuel selector positioned to the "right" position. Historical uneven fuel consumption greater from the left tank was noted while operating the airplane in skydiving operations that involve mainly climbs and descents. After repairs, the engine was placed on the airframe and operated with no discrepancies noted. Post accident testing with an exemplar carburetor, the accident fuel strainer and flexible hose from the fuel strainer to the carburetor with the assembly placed inverted revealed the carburetor leaks fluid to a certain level but fluid remains in the bowl. Additionally, with the assembly inverted and the carburetor bowl empty but fluid in the fuel strainer and flexible line, fluid does not flow into the carburetor bowl. The fuel selector valve was repaired last on March 18, 1977, in which an o-ring on the fuel selector shaft was replaced.