What happened
The aircraft was involved in a flight incident where the engine failed during operation. Following the mechanical failure, the pilot initiated an autorotative landing procedure to manage the descent without power. During this maneuver, the helicopter's tail rotor made contact with the ground surface. The accident site was characterized by significant snow accumulation, with depths varying between 32 and 45 inches. The impact with the snow-covered terrain resulted in damage to the tail rotor assembly.
The investigation
A mechanical examination of the aircraft's engine was conducted to determine the root cause of the power loss. The inspection revealed that the right-hand magneto was firing intermittently. Specifically, two of the six distributor contacts were found to be gapped closer than the prescribed minimum specification. This improper gap likely contributed to the inconsistent ignition and subsequent engine failure.
Findings
The investigation identified several contributing factors to the accident sequence. The primary mechanical issue was the incorrect gap setting on the distributor contacts within the magneto system. This maintenance error led to intermittent firing, which caused the engine to fail. Additionally, the environmental conditions played a role in the severity of the outcome; the deep snow required the pilot to execute a low-altitude autorotation where the tail rotor clearance was critically reduced.
Safety message
This incident highlights the critical importance of adhering to precise maintenance specifications for ignition systems. Even minor deviations in distributor contact gaps can lead to intermittent engine operation and catastrophic failure. Pilots operating in environments with variable ground conditions, such as deep snow, must also be aware of the reduced clearance margins during autorotative landings.