CHI02LA087 · Cessna 182H

The airplane sustained substantial damage during a forced landing to a field after a total loss of engine power. The pilot reported he was cruising at 3,000 feet msl when he heard a loud bang from the engine, followed almost immediately by smoke from beneath the left side panel and excessive vibration from the engine. The engine lost power and the pilot executed a forced landing. During landing roll out, the nose wheel struck a rock and the nose gear collapsed. An inspection of the engine revealed that a connecting rod had punched a hole in the engine case. The number 2 piston rod, rod bearing, and rod journal were discolored and exhibited heat distress. The crankshaft was broken in two pieces at the number 2 cheek. A fatigue fracture was observed on the fracture surfaces of the number 2 cheek. The engine was originally a 230 horsepower Continental O-470-R that was converted to a 270 horsepower O-470-50, as a result of Supplemental Type Certificate (STC) #SE4985NM. This STC required the cylinders to be replaced with the same cylinders and pistons used on Continental O-520 engines. The crankshaft, forging number 539664, S/N S401, and heat code E99, referred to as a "wide-rod" crankshaft, was manufactured in the 1960's and was originally used on Continental Motors O-470 and IO-470 engines. The crankshaft had not been replaced since the STC conversion on December 23, 1994. It had accumulated 1,259.0 hours since the STC conversion. The engine teardown revealed that the pistons installed on the engine were 8.5 to 1 compression pistons used on normally aspirated Continental O-520 engines. The P. Ponk Aviation STC SE4985NM specifies that the 7.5 to 1 compression pistons are the proper pistons to use in the engine conversion. On September 24, 2002, P. PONK AVIATION, issued a Service Information Letter, SIL 002, that stated, "Use of the "wide-rod" crankshaft with any piston higher than the 7.5 to 1 compression ratio and a maximum rpm above 2700 is not authorized by our STC and could result in engine failure. Our testing did not exceed the above parameters, and we do not condone or support installation of the higher compression pistons." No logbook entries indicated any of the pistons had been changed since the engine was converted to an O-470-50, on December 23, 1994, and only the # 3 cylinder was changed on April 15, 2000, due to low compression. The engine build-up records that documented what parts were installed on the engine during the STC conversion no longer existed.

Verbatim NTSB analysis and probable cause from the NTSB dataset