Event
The flight departed uneventfully and landed at La Belle Municipal Airport. The departure return flight proceeded, but during cruise, the certified flight instructor (CFI) noted a discrepancy with one fuel gauge. He landed at a nearby airport and, with the engine running, checked for fuel leaks and both tanks; no leaks were found and both tanks had sufficient fuel. The CFI then departed for the original airport. Approximately 15 minutes into the flight, oil spots appeared on the windshield, and shortly after, the engine lost power. The CFI maneuvered for a field landing at 85 mph with flaps retracted. During the landing roll, the airplane collided with a berm, became airborne, then contacted another berm, became airborne again, and finally impacted the ground and came to rest upright. The CFI exited and obtained assistance for the student, who remained in the airplane.
Investigation
Examination of the fuel system, fuel vent system, air induction system, exhaust system, and engine assembly revealed no preimpact failure or malfunction. The crankshaft fracture was due to overstress. Ignition system components showed no preimpact failure; however, bench testing of both magnetos noted a discrepancy with their condensers. Fuel injection components, fuel selector valve, and flexible fuel lines showed no preimpact failure. Fuel from the fueling facility tested without discrepancies that would cause a loss of engine power. No determination was made as to the reason for the reported loss of engine power. The airplane's flight manual specifies that for forced landings on unprepared surfaces, full flaps should be used if possible with a 75 mph glide.