On March 30, 1997, at 1530 central standard time, a Beech M35 airplane, N223C, registered to and operated by a private owner, was substantially damaged during a forced landing following a loss of engine power near Iowa Park, Texas. The private pilot and his passenger were not injured. Visual meteorological conditions prevailed for the Title 14 CFR Part 91 personal flight. A flight plan was not filed for the local flight which was originating at the time of the accident.

During a telephone interview conducted by the NTSB investigator-in-charge and on the NTSB Pilot/Operator Aircraft Accident Report, the pilot stated that the airplane was on its initial takeoff climb from the Wichita Valley Airport when the engine seized and oil splashed onto the windshield. He made a forced landing in a wheat field close to the airport. During the landing roll, the airplane impacted an "unseen drainage ditch." Examination of the airplane by an FAA inspector revealed that both wing spars were bent and the fuselage was twisted.

An engine teardown was performed under the supervision of an NTSB investigator at Air Salvage of Dallas in Lancaster, Texas, on April 3, 1997. During removal of the engine from the airframe, a portion of the number 4 connecting rod with its respective piston pin attached was found in the forward area of the cowling. Three holes were noted in the crankcase. During disassembly, it was found that the numbers 3 and 4 pistons had separated from their piston pins, and these pistons were lodged in the top of their respective cylinders. The number 1, 2, 5, and 6 pistons were cracked. Numerous metal pieces were found in the oil sump and throughout the whole engine. A fuel sample was taken; the fuel was yellow in color and had a strong gasoline odor.

A review of the Limitations Section of the Beechcraft Bonanza K35 and M35 Pilot's Operating Handbook revealed that the minimum octane grade of fuel approved for use in the airplane was 100. On the Pilot/Operator Report, the pilot indicated the airplane had a mixture of 100 Low Lead and automotive fuel on board at the time of the accident. A laboratory analysis of the fuel sample performed by the Armstrong Forensic Laboratory, Inc., of Arlington, Texas, established the fuel to be automotive gasoline (octane grade 87 to 92).

Regarding the octane grades of fuel, FAA Advisory Circular (AC) 61-23B, Pilot's Handbook of Aeronautical Knowledge, states the following:

The proper fuel for an engine will burn smoothly from the spark plug outward, exerting a smooth pressure downward on the piston. Using a low-grade fuel or to lean a mixture can cause detonation. Detonation or knock is a sudden explosion or shock to a small area of the piston top, similar to striking it with a hammer.

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