What happened
On June 08, 2013, a Eurocopter EC 130 B4, registration N130PH, was conducting a training flight near the Grand Canyon, Arizona. The flight was operated by Papillon Grand Canyon Helicopters for the purpose of instructing a newly hired pilot. The flight departed Grand Canyon National Park Airport (GCN) at approximately 0815 with a planned destination of Valle Airport (40G).
During the flight, the certified flight instructor (CFI) performed several maneuvers, including a simulated engine failure. While descending through 200 feet above ground level (agl) and attempting to increase engine power to terminate the maneuver, the CFI found that the throttle twist grip had seized. Unable to manipulate the control, the CFI performed a full down autorotation.
The helicopter touched down on dirt terrain approximately 3 nautical miles northeast of Valle Airport. Upon landing, a skid became caught in the soft ground, causing the nose to tip downward. This movement caused the main rotor blades to strike and sever the tailboom. The crew, consisting of the CFI and the pilot undergoing instruction, were not injured, though the aircraft sustained substantial damage.
The investigation
Investigators from American Eurocopter and the FAA examined the collective components. The inspection revealed several abnormalities, including:
- The return coil spring in the pilot's twist grip control was found out of its notched seat on the tube assembly, which could make moving the throttle between idle and flight positions difficult.
- The co-pilot's side torque tube rack teeth showed a small amount of foreign object damage (FOD).
- The co-pilot's side electrical wiring harness exhibited pinching damage where it entered the center of the collective.
- The twist grip handle showed heavy wear, with the black powder coat paint worn off, suggesting the control was stiff or difficult to manipulate.
- The rubber shield exiting the collective was bent due to the operator's storage methods and showed tearing near the engagement notch.
Despite these findings, investigators were unable to reproduce the throttle jamming during subsequent testing, and the examination failed to identify a specific cause for the loss of throttle movement.
Findings
Following the accident, the operator implemented changes to its normal operating procedures. Company instructors are now required to attend the manufacturer's factory flight school for training, and manipulations of the throttle twist grip are prohibited unless the aircraft is over a hard landing surface at an airport.