What happened
During the cruise portion of the flight at an altitude of 9,500 feet, the aircraft's engine seized completely. The pilot initiated a forced landing procedure and selected a divided highway as the landing site. Due to the presence of traffic on the roadway, the pilot was compelled to aim for the median strip. During the touchdown, the left wing struck a roadside sign, causing the aircraft to veer off course and enter a ditch.
The investigation
Post-accident examination of the engine revealed significant mechanical failures consistent with improper maintenance. Specifically, the rear crankcase through bolts were found to be only finger tight rather than torqued to specification. This lack of proper fastening allowed the rear main bearing to spin within its housing. Consequently, the number one connecting rod cap separated from the piston assembly, and the crankshaft fractured through the counterweight cheek.
Findings
The engine had accumulated 121 hours since its last overhaul at the time of the incident. The primary cause of the failure was identified as inadequate maintenance during the overhaul process, specifically the failure to properly torque the rear crankcase through bolts. This oversight led to the disintegration of the internal rotating assembly and the subsequent loss of power in flight.
Safety message
This incident highlights the critical importance of adhering to strict torque specifications during engine overhaul procedures. Proper installation of crankcase fasteners is essential to prevent catastrophic bearing failure and subsequent engine seizure.