On March 29, 2002, a Beech D35 (registration N2966B) was involved in an aviation accident near Nacogdoches, TX. Investigators recorded the probable cause as: 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. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A single-engine airplane crashed into a creek bed after the engine lost power during a cross-country flight. Investigation found severe wear in the engine-driven fuel pump drive pin and rotor holes.
Accident Overview and Flight Sequence During a personnel cross-country flight under night visual meteorological conditions, a single-engine airplane experienced a loss of engine power while in cruise. The pilot reported performing emergency procedures, including operating the wobble pump, also known as the manual fuel pump, but the engine did not restart. During the emergency descent toward a road, the airplane struck trees, inverted, descended, and came to rest in a creek bed. ## Maintenance and Inspection History Maintenance records showed that in April 1993, at 4,110.0 accumulated engine hours, the engine was removed, overhauled, and reinstalled. On June 10, 1983, the wobble pump and fuel system were checked. The last annual inspection was performed on November 4, 2001, at 8,117 accumulated airframe hours, and a 100-hour inspection was completed at 980.15 hours since major overhaul. At the time of the accident, the airplane had accumulated 27.1 hours since the last annual inspection. ## Post-Accident Examination Flight control continuity was confirmed, and the auxiliary wobble pump handle was found in its stowed position. When the engine-driven fuel pump was removed, the splines engaging the pump into the engine accessory section were intact, but the pin connecting the drive coupling to the fuel pump drive shaft was separated. The NTSB metallurgist examined the Thompson Ramo Woolridge Incorporated engine-driven fuel pump, model TF1900, serial number TF45071, and the splined drive. The pump housing contains a rotor whose hollow end 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, and the shaft ends are attached by a pin. Visual examination showed that a pin was installed on the shaft end of the driver, with severely worn ends. The pin measured approximately 0.310 inch in length, while the spline gears showed no evidence of wear. ## Rotor Wear and Service Bulletin Findings The mounting flange was disassembled from the pump housing to expose part of the hollow shaft end of the rotor. The end of the rotor shaft portion has two sets of holes, totaling four holes, spaced equally around the circumference. Continental Motors Corporation Service Bulletin ESD 182D required measuring the diameter of these holes in the circumferential and axial directions. If the circumferential diameter exceeded the axial diameter by more than 0.015 inch, the rotor had to be replaced. The rotor could be reused if either set of holes was worn less than 0.015 inch and the drive pin was installed in the unworn set. If both sets of holes were worn beyond 0.015 inch, the rotor should be discarded and the pump overhauled. The hole walls exhibited severe wear and elongation in the circumferential direction. The circumferential diameters measured 0.1500, 0.1430, 0.1510, and 0.1730 inch, while the axial diameters measured 0.1185, 0.1250, 0.1255, and 0.1225 inch, respectively. These circumferential diameters exceeded the 0.015 wear limits specified in the service bulletin. 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 at 0.310 inch. ## Testing and Additional Findings Using an exemplary engine-driven fuel pump, the post-accident engine run sustained 2,450 rpm and 28 inches of manifold pressure. The accident airplane's fuel selector valve and auxiliary wobble pump were plumbed into the test stand fuel system. The exemplary engine-driven fuel pump was removed, and the engine was started using the auxiliary wobble pump. With only the wobble pump supplying fuel, the engine sustained 2,450 rpm and 28 inches of manifold pressure in both left and right fuel selector valve positions. Examination and flow testing of the carburetor revealed that a four-tube discharge nozzle was installed, while the manufacturer's representative stated the correct nozzle has six discharge tubes. 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, while all other test points were within specifications.