Accident Sequence
The airplane was on its initial takeoff climb when the engine lost power. The pilot performed a forced landing in a field. During the landing roll, the airplane impacted a ditch.
Engine Examination
An engine teardown revealed that the number 1, 2, 5, and 6 pistons were cracked. The number 3 and 4 pistons had separated from their piston pins and were lodged in the top of their respective cylinders.
Fuel Analysis
An analysis of the fuel found in the airplane established that it was automotive gasoline with an octane grade of 87 to 92. According to the limitations section of the Pilot's Operating Handbook, the minimum octane grade of fuel approved for use in the airplane was 100. The use of low-grade fuel can lead to detonation, which is defined in FAA Advisory Circular 61-23B as a sudden explosion or shock to a small area of the piston top.