ERA24LA139 · Beech K35

The pilot was conducting an extended duration aerial survey flight. He reported that he had experienced anomalies with the propeller controls and the No. 3 cylinder exhaust gas temperature (EGT) during the flight. After about 5 and ½ hours of flying, he became uncomfortable with the EGT values and chose to suspend the survey and land. He began to climb the airplane while enroute to the destination. During the climb, he attempted to switch the fuel selector from the right main to the left main fuel tank, and several minutes later, the engine began to stumble. He double-checked the fuel selector, noted that it was on an auxiliary tank, then moved it to the left main tank position. He reported that shortly thereafter the engine lost total power. He was unable to reach the destination airport and performed a forced landing to a field, during which the airplane was substantially damaged. The airplane was equipped with two bladder-type main fuel tanks, one per wing, each with a capacity of 25 gallons of which 3 gallons were unusable; and two bladder-type auxiliary fuel tanks, each with a 20-gallon capacity of which 1 gallon was unusable. The airplane was also equipped with fiberglass wingtip tanks. The pilot reported that he departed on the accident flight with all of the fuel tanks filled to their capacity. The main and auxiliary fuel tanks were not breached during the accident sequence, while the wingtip tanks remained attached to the wings but were both ruptured. Personnel who recovered the airplane from the accident site collected about 5 gallons of fuel from the right wing fuel tanks and less than 1 gallon of fuel from the left wing fuel tanks. A subsequent airframe inspection, engine test run, test of the oil transfer collar, and a propeller governor bench test were conducted, and all revealed no evidence of preimpact mechanical malfunctions or failures that would have resulted in a total loss of engine power. Examination of data from the airplane’s engine data monitor revealed that shortly before the engine lost power, the fuel flow and pressure values suddenly decreased to 0, after which the cylinder head temperature (CHT) and EGT also began decreasing. The data were consistent with an interruption of fuel flow to the engine, resulting in a total loss of engine power. In summary, the data which suggest the loss of engine power was preceded by an interruption of fuel flow, the successful posaccident test run of the engine, the lack of any mechanical anomalies found during the poaccident examinations and test runs of the engine and its subcomponents, combined with the limited amount of fuel recovered from the airplane after the accident, were all indicative that the loss of engine power was most likely the result of fuel starvation.

Verbatim NTSB analysis and probable cause from the NTSB dataset