The pilot stated that during cruise flight at 3,500 feet above mean sea level and 120 mph, there was a loud repeating banging sound and a loss of engine power.
Engine oil temperature increased to 220°F, engine oil pressure decreased below 35 psi, and engine oil sprayed onto the Cessna 170A’s windshield.
As the airplane descended, he looked for an area to perform a forced landing near Marshall, Indiana. He planned to land on a short open area, but overshot the open area because he could not dissipate enough of the airplane’s energy. He then landed on a corn field where the airplane contacted the corn, nosed over, and hit the ground.
The airplane sustained substantial damage to the wings, vertical stabilizer, and rudder, while the pilot received minor injuries.
Post-accident examination of the engine revealed a hole in the crankcase above the No. 6 cylinder assembly. The No. 6 connecting rod was fractured near its base.
Metallurgical examination of the No. 6 connecting rod revealed fracture features that were consistent with fatigue cracking. The cracks initiated at multiple locations on the outer surface opposite the inner bearing surfaces that mated the crankshaft. These cracks propagated through most of the rod yoke arm cross section until the remainder subsequently fractured from tensile overstress. All other fracture surfaces were consistent with overstress fracture.
Maintenance records showed the engine received a major overhaul on Sept. 27, 2010. The last annual inspection on the engine was dated March 1, 2024, and the engine had 572.7 hours since the major overhaul. Continental manual M-O Ch. 6-3, Table 6-1 states: C125, C145 series, and O-300-A,B,C,D engines have a time between overhauls of 1,800 hours or 12 years, whichever comes first.
Probable Cause: The fatigue fracture of the No. 6 piston connecting rod, which resulted in a loss of engine power.
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This September 2024 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
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