What happened
The aircraft experienced an in-flight loss of engine power due to the complete depletion of lubricating oil. This failure occurred because oil escaped through a hole in the rocker box cover, which was caused by five of the six securing screws being absent. The remaining hardware allowed the cover to vibrate against the rock arm, creating the breach.
During the subsequent forced landing attempt, the aircraft collided with powerlines. The pilot and owner reported that he had inspected all nuts and bolts just 16 flight hours prior to the accident.
The investigation
The mechanical examination focused on the engine's lubrication system and securing hardware. Investigators found that the rocker box cover was not properly fastened, allowing it to vibrate against the rock arm. This vibration created a hole through which all oil was lost from the engine in flight.
Findings
The primary contributing factor was the fuel exhaustion equivalent of lubrication failure due to mechanical disassembly. Specifically, the engine suffered catastrophic oil loss because five of six securing screws were missing from the rocker box cover. The pilot had performed a visual inspection of fasteners shortly before flight but failed to detect the missing hardware.
Safety message
This incident highlights the critical importance of thorough pre-flight inspections, particularly for engine mounting and accessory drive components. Visual checks must be meticulous, as loose or missing fasteners can lead to rapid mechanical failure.