What happened
The aircraft was engaged in a sling load operation when the engine experienced a sudden loss of power while the helicopter was hovering. In response to the emergency, the pilot released the external load. However, due to low rotor revolutions per minute (RPM), the aircraft descended rapidly and landed hard, resulting in substantial damage to the airframe.
The investigation
Examination of the wreckage revealed specific mechanical failures that contributed to the power loss. The forward male splines on the spin adapter gearshaft had failed. Additionally, inspection of the fuel system showed that the fuel nozzle screen had collapsed and was clogged with fibrous debris, which likely restricted fuel flow to the engine.
Findings
The sequence of events indicates that a mechanical failure in the drive system combined with a blockage in the fuel supply led to the engine stoppage. The pilot's decision to release the load was appropriate given the loss of power, but the low rotor RPM prevented a controlled landing. The fibrous debris found on the fuel nozzle screen suggests a maintenance or contamination issue that compromised the engine's ability to function.
Safety message
Regular inspection of fuel system components, particularly screens and filters, is critical to prevent blockages from fibrous debris. Maintenance procedures should ensure that spin adapter gearshafts are checked for spline integrity to avoid catastrophic drive failures during critical flight phases such as hovering.