Incident Overview
An aircraft on a forest fire spotting mission departed from Kissimmee, Florida. During the flight, the engine began to run rough and subsequently lost power. The pilot executed a forced landing in an orange grove, during which the airplane struck a tree.
Engine Examination
Examination of the engine revealed that improper connecting rod bolts had been used. Specifically, the bolts in two connecting rods failed, leading to engine failure. Investigation traced the bolts to manufacturing in the 1980s, and they became available in the U.S. market in February 1994. A repair station obtained these bolts in June 1994 and installed them in connecting rod assemblies that were in storage. The overhaul date on the work order for the stored rod assemblies was not updated at that time, continuing to indicate an overhaul date of February 9, 1994.
Subsequent Overhaul and Airworthiness Directive
The stored rod assemblies were later installed in the engine during an overhaul in October 1994. In March 1995, an Airworthiness Directive (AD) was issued requiring inspection of engines with connecting rod bolts installed on or after February 15, 1994. However, the AD was not complied with on this engine because the repair station certified that the rod assemblies had been overhauled on February 9, 1994, which was before the effective date of the AD.
Conclusion
The engine failure was caused by the use of improper connecting rod bolts, which failed in two connecting rods. The failure sequence involved bolts manufactured in the 1980s that were not subject to the mandated inspection due to incorrect documentation.