What happened
The incident occurred while a helicopter was attempting to lift off from an elevated platform situated on top of a loading truck. As the aircraft began its ascent, the pilot experienced a sudden and significant loss of engine power, accompanied by a loud bang heard inside the cockpit. Recognizing the critical nature of the failure, the pilot utilized the kinetic energy stored in the rotating rotor system to maintain some degree of control. The objective was to guide the helicopter away from the immediate hazards of the stand and the truck below. Despite these efforts, the aircraft was unable to sustain flight and descended rapidly, ultimately colliding with the terrain below.
The investigation
Following the accident, investigators examined the helicopter's mechanical systems to determine the root cause of the power loss. A detailed inspection of the engine revealed a critical internal failure. Specifically, a fractured intake valve retainer, also known as a keeper, was found in the number one cylinder. This component is essential for keeping the valve in place during operation; its failure would disrupt the engine's ability to function properly.
Findings
The mechanical failure of the intake valve retainer in the number one cylinder directly caused the loss of engine power. The pilot's decision to use rotor inertia was a standard emergency procedure, but the altitude and proximity to the elevated stand left insufficient margin for recovery. The collision with the terrain was the direct result of this unrecoverable power loss during the initial phase of flight from a non-standard takeoff surface.