What happened
The incident occurred during a maintenance flight check conducted after a turbine replacement had been performed on the aircraft. During this test flight, the helicopter experienced a total loss of engine power. In response to the emergency, the pilot initiated an autorotation and began to cushion the descent using the collective pitch control.
As the helicopter approached the ground, it touched down and rocked forward before rocking back again. The violent motion resulted in the main rotors striking and severing the tailboom. This structural failure caused significant damage to the rear section of the aircraft.
The investigation
Following the accident, investigators examined the engine to determine the root cause of the sudden power loss. The mechanical inspection revealed a critical internal failure within the engine assembly.
Specifically, the examination found a lack of oil supply to the number eight bearing assembly. This lubrication failure likely contributed to the seizure or malfunction that led to the total loss of engine power during the flight check.
Findings
The primary factor in this accident was the mechanical failure of the engine due to insufficient lubrication. The specific component affected was the number eight bearing assembly, which did not receive the necessary oil flow to operate correctly.
The sequence of events indicates that the maintenance flight check served as the operational context for the discovery of this defect. The subsequent autorotation and landing attempt were standard emergency procedures, but the structural integrity of the tailboom could not withstand the forces generated during the touchdown and rocking motion.
Safety message
This incident highlights the importance of thorough post-maintenance testing procedures. Ensuring that all lubrication systems are properly filled and functioning before flight is critical. Maintenance checks should verify that oil passages are clear and that bearings receive adequate supply to prevent in-flight power loss.