Incident Overview
While in cruise flight, the aircraft experienced an engine failure that necessitated a ditching in a river. The subsequent post-crash examination focused on the engine to determine the cause of the failure.
Examination Findings
Inspection of the engine revealed that the No. 1 and No. 2 connecting rods had separated from the crankshaft. The separation occurred because both bolts on the No. 1 connecting rod failed, and one bolt on the No. 2 connecting rod failed.
Metallurgical Analysis
A metallurgical examination of the failed bolts was conducted. The Rockwell hardness of the No. 1 rod bolts varied significantly across different points, ranging from 26 to 44. The failed No. 2 rod bolt showed less variation, with hardness between 41.6 and 42.2.
Microstructure analysis of the failed bolts indicated structural inconsistencies. Near areas of low hardness, the structure was primarily ferrite, while near higher hardness areas, it was primarily martensite. This change in microstructure suggests that the bolts were subjected to excessive heat, although no obvious blockages were found in the lubrication system.
Crankshaft Journal Condition
Further examination of the No. 1 and No. 2 connecting rod crankshaft journals revealed evidence of scoring and darkening, consistent with abnormal operating conditions.