Aircraft Accident/Incident Report

Nacogdoches, Texas 75961
Friday, March 29, 2002 21:30

Night visual meteorological conditions prevailed for the personnel cross-country flight. The pilot reported that the single-engine airplane was in cruise flight when the engine lost power. The pilot stated that he performed the emergency procedures including the wobble pump (manual fuel pump); however, the engine did not restart. During the emergency descent to a road, the airplane struck trees, went to an inverted attitude, descended, and came to rest in a creek bed. Maintenance records indicated that in April 1993, at the accumulated engine time of 4,110.0 hours, the engine was removed, overhauled and reinstalled. On June 10, 1983, the wobble pump and fuel system were checked. On November 4, 2001, the last annual inspection was performed at the accumulated airframe time of 8,117 hours, and 100 hour inspection performed at the accumulated engine time of 980.15 hours since major overhaul (TSMOH). The airplane had accumulated 27.1 hours since the last annual inspection. Flight control continuity was confirmed. The auxiliary (wobble pump) handle was found in its stowed position. When the engine driven fuel pump was removed from the engine, the splines that engage the pump into the engine accessory section were intact; however, the pin that engages the drive coupling to the fuel pump drive shaft was found separated. The Thompson Ramo Woolridge Incorporated engine drive fuel pump (model TF1900, S/N TF45071), and splined drive were examined by the NTSB metallurgist. The housing for the fuel pump contains a rotor. The hollow end of this rotor is exposed to the outside surface of the pump. In the installed condition, the shaft end of the driver is partially inserted into the hollow shaft end of the rotor. The shaft ends of both parts are attached to each other by a pin. Visual examination of the pump pieces revealed that a pin was installed on the shaft end of the driver. The ends of the pin were severely worn. The length of the pin measured approximately 0.310 inch. The spline gears showed no evidence of wear. The mounting flange was disassembled from the pump housing to expose a portion of the hollow shaft end of the rotor. The end of the shaft portion of the rotor has two sets of holes (a total of 4 holes). The holes are spaced equally around the circumference of the shaft. Continental Motors Corporation Service Bulletin (SB) ESD 182D indicated that the diameter of these holes should be measured in the circumferential and axial directions of the shaft. If the diameter in the circumferential direction exceeds the diameter in the axial direction by more that 0.015 inch, the rotor must be replaced. The rotor can be reused if either set of holes is worn less than 0.015 inch and the drive pin is installed in the unworn set of holes. According to the SB, the rotor should be discarded and the pump should be overhauled if both sets of holes are worn beyond 0.015 inch. The wall of the holes exhibited severe wear and was elongated in the circumferential direction. The diameter of the worn hole in the circumferential direction measured 0.1500, 0.1430, 0.1510, and 0.1730 inch. The diameter of the hole in the axial direction measured 0.1185, 0.1250, 0.1255, and 0.1225 inch, respectively. The diameter of the holes in the circumferential direction exceed the 0.015 wear limits specified in the SB. The inside diameter of the hollow end of the rotor measured approximately 0.313 inch, which was greater than the measured length of the worn pin (0.310 inch). Utilizing an exemplary engine driven fuel pump, et al, the post-accident engine run sustained 2,450 rpm's and 28 inches manifold pressure. The accident airplane fuel selector valve/auxiliary fuel pump (wobble pump) was plumbed into the test stand fuel system. The exemplary engine driven fuel pump was removed from the engine, and the engine was started with the auxiliary fuel pump (wobble pump). Utilizing the wobble pump, the engine sustained 2,450 rpm's and 28 inches of manifold pressure with only the wobble pump supplying fuel to the engine with the fuel selector valve (left and right) positions. Examination and flow testing of the carburetor revealed that a four tube discharge nozzle was found installed in the carburetor. According to the manufacturer’s representative, the correct nozzle has six discharge tubes for the carburetor. Auto gas was evident inside the carburetor. During the flow test, no external leaks were noted. Test points 1,3,4,5, and 11 were under the minimum limits, and all other test points were within specifications.

The failure of the engine driven fuel pump drive pin resulted in a total loss of engine power. Contributing factors were inadequate maintenance, the pilot's inadequate use of the manual auxillary fuel pump (wobble pump), and the night conditions.