NTSB Identification: FTW97LA147.
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Accident occurred Sunday, March 30, 1997 in IOWA PARK, TX
Probable Cause Approval Date: 08/25/1997
Aircraft: Beech M35, registration: N223C
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The airplane was on its initial takeoff climb when the engine lost power. The pilot performed a forced landing in a field, and during the landing roll, the airplane impacted a ditch. An engine teardown revealed that the number 1, 2, 5, and 6 pistons were cracked, and the number 3 and 4 pistons had separated from their piston pins and were lodged in the top of their respective cylinders. An analysis of the fuel found in the airplane established that it was automotive gasoline (octane grade 87 to 92). As listed in 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.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The pilot's refueling of the airplane with automotive grade fuel which resulted in engine failure due to detonation. A factor was the lack of suitable terrain for the forced landing.

Full narrative available

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