What happened
The aircraft experienced a complete loss of engine power while on final approach for landing at approximately 100 feet above ground level. The pilot initiated an autorotational descent to avoid a crash into terrain or structures. Upon impact with the soft ground, the force of the landing was sufficient to sever the helicopter's tail boom.
The investigation
Post-accident examination of the engine revealed a critical mechanical defect. The point gap on the left magneto was found to be excessively closed, preventing proper spark generation on that side. To verify the diagnosis, a test run was conducted where the 'P' lead for the left magneto was disconnected. During this test, the engine continued to operate solely on the right magneto, confirming that the left system was non-functional and likely contributed to the power loss during flight.
Findings
The primary factor leading to the accident was the mechanical failure of the ignition system. Specifically, the left magneto point gap being excessively closed prevented the engine from running on both magnetos as designed. This defect resulted in a significant reduction in power output or complete failure under certain conditions, culminating in the loss of power during the critical final approach phase. The subsequent autorotational landing, while executed to prevent a more severe impact, resulted in substantial structural damage due to the hard contact with the ground.
Safety message
Regular inspection and adjustment of magneto point gaps are essential for maintaining reliable engine performance. Pilots and mechanics should ensure that ignition systems are functioning correctly on both magnetos to prevent partial or total power loss during critical phases of flight.