WPR11LA374 · SIAI Marchetti F.260

The day before the accident, the pilot flew himself and his family to an airport about 275 miles away for the purpose of positioning the airplane for filming. The airplane was flown by another pilot during that filming, which was accomplished on the day of the accident. After the filming, the airplane was fueled, and the pilot and his family departed on their return trip. En route to the destination, the pilot diverted to another airport because one of the children did not feel well. They spent about 20 minutes at that airport, and then re-boarded the airplane to complete the trip. Engine start, runup, and the takeoff roll were normal, but when the airplane was about 100 feet above ground level, the engine began to lose power. The pilot pushed the nose down to maintain his target airspeed, but the airplane continued to decelerate. The pilot then landed straight ahead in a plowed field off the end of the runway. Initial examination of the airplane and engine did not reveal any preimpact discrepancies that would have precluded continued flight.

Normal procedures call for the takeoff to be conducted with the electric fuel boost pumps operating and then switched off during the climb. The pilot reported that the boost pump switch was on for takeoff and that he did not turn it off before the engine power loss. Postaccident engine test runs revealed that the engine would not run at high rpm without the boost pumps operating. Further examination and testing revealed that a fuel check valve, designed to ensure sufficient fuel flow to the carburetor when the fuel boost pumps were not operating, did not function properly due to a deteriorated gasket. As a result, fuel from the engine driven pump could be pumped back into the fuel tanks instead of into the carburetor. Although the engine test runs demonstrated that, due to the failed check valve, the engine would not run at high rpm without the electric boost pumps, the investigation was unable to determine why the deteriorated check valve did not manifest itself on previous flights. Because the pilot reported that he did not turn off the boost pumps on the accident flight, the defective check valve likely did not cause the loss of engine power.

A chart for carburetor icing potential indicated that conditions were conducive to icing at glide and cruise power. Even if the airplane had developed carburetor ice on the approach, it is likely that the 20 minutes spent on the ground, at an ambient air temperature of 33 degrees, would have melted that ice. The fact that the power loss occurred with the engine at takeoff power suggested that while takeoff carburetor ice might have been possible, it was not likely. The temporary nature of carburetor ice, combined with the fact that the airplane was not examined in detail immediately subsequent to the accident, precluded the investigation from determining whether carburetor icing was present at the time of the power loss.

Finally, because the fuel quantities in the low-wing airplane were relatively low, the resultant head pressure in the fuel lines would be low. This, in combination with the hot engine and the 20-minute ground time on a hot ramp at an airport with an ambient temperature of 33 degrees C, could have precipitated partial or full vapor lock in the fuel system, which did not manifest itself until the takeoff demanded full power and maximum fuel flow. The investigation was not able to determine whether the source of the power loss was fuel system vapor lock or carburetor ice.

Verbatim NTSB analysis and probable cause from the NTSB dataset