What happened
The incident occurred while the helicopter was in the process of taking off. During this phase, the crew experienced an immediate loss of rotor revolutions per minute (RPM). This mechanical failure was accompanied by a simultaneous cessation of fuel flow to the engine.
In response to these critical system failures, the pilot initiated an abort of the takeoff maneuver. The aircraft returned to the ground for a touchdown. However, during the impact with the surface, the main rotor blades flexed downward significantly. This flexing caused the blades to strike and sever the tail boom of the helicopter.
The investigation
Following the accident, investigators conducted a detailed inspection of the engine compartment to determine the root cause of the fuel flow interruption. The examination revealed a specific mechanical failure within the fuel delivery system. A 'B' nut located on an air line connecting the governor and the fuel control unit was found to be both cracked and loose.
This compromised fitting allowed for significant leakage within the system, which directly resulted in the loss of fuel pressure required to maintain engine operation and rotor RPM during the critical takeoff phase.
Findings
The primary contributing factor to this accident was the mechanical failure of the fuel system. The cracked and loose 'B' nut on the air line between the governor and the fuel control unit permitted system leakage. This leakage caused the loss of fuel flow, which led to the loss of rotor RPM. The subsequent flexing of the main rotor blades during the aborted takeoff touchdown resulted in damage to the tail boom.
fuel system leakage was the critical event that initiated the chain of failures leading to the accident.