What happened
The accident occurred while the aircraft was on final approach for touchdown. At a low altitude, the pilot experienced a sudden loss of power. To clear power lines that crossed the approach path, the pilot bled off rotor revolutions per minute (RPM). This maneuver depleted the rotor system's stored energy, which is critical for maintaining control during an autorotation. Consequently, the aircraft was unable to execute a safe autorotative landing and impacted the ground with significant force.
The investigation
Examination of the operational context revealed that carburetor heat was not utilized except during the initial engine runup. Despite weather conditions being favorable for carburetor ice formation, the pilot's decision to bleed off rotor RPM directly contributed to the loss of energy required for a controlled descent.
Findings
The primary factor in this accident was the loss of rotor energy due to excessive RPM bleed-off during a low-altitude maneuver. The lack of available rotor inertia prevented the pilot from sustaining an autorotation, resulting in a hard landing. While carburetor ice may have contributed to the initial power loss, the immediate cause of the crash was the inability to maintain rotor speed necessary for a safe emergency landing.