Accident Details
On June 8, 2013, at about 0935 mountain standard time, a Eurocopter EC 130 B4 (registration N130PH) experienced an engine control malfunction while performing practice autorotation maneuvers near Grand Canyon, Arizona. The helicopter was owned by American Helicopters LLC and operated by Papillion Grand Canyon Helicopters under 14 CFR Part 91. The certified flight instructor (CFI) and pilot undergoing instruction (PUI) were not injured; the helicopter sustained substantial damage.
The training flight departed Grand Canyon National Park Airport (GCN) at about 0815, with a planned destination of Valle Airport (40G). Visual meteorological conditions prevailed, and no flight plan was filed.
Flight Maneuver and Malfunction
The purpose of the flight was for the CFI to provide instruction to the PUI, who had recently been hired by the operator. After performing numerous maneuvers, the CFI conducted a simulated engine failure, intended to terminate with a power recovery. During the maneuver, the CFI configured the helicopter for an appropriate airspeed, and while descending through 200 feet above ground level, he began to roll in the throttle to increase engine power. The throttle twist grip seized, and he could not manipulate the control to increase power.
The CFI performed a full down autorotation. The helicopter touched down on dirt terrain. The nose tipped downward, then it rocked back on the skids, resulting in the main rotor blades severing the tailboom. The helicopter came to rest about 3 nautical miles northeast of Valle Airport.
Post-Accident Examination
American Eurocopter personnel examined the collective components under FAA supervision. Findings included:
- The grab on the return coil spring in the pilot's twist grip control was out of its notched seat on the tube assembly, making the throttle twist grip more difficult to move into/out of FLIGHT from IDLE.
- The co-pilot's side torque tube rack teeth exhibited a small amount of foreign object damage (FOD) relative to the collective pitch torque tube block.
- The co-pilot's side electrical wiring harness showed pinching damage where it entered the center of the collective.
- The twist grip handle was heavily worn; the black powder coat paint was worn off, indicating the pilot collective was stiff or harder to manipulate than normal.
The examination failed to reveal the cause of the collective twist grip failure, and further examination with the airframe was scheduled.
On January 14, 2014, investigators examined the helicopter and components at Papillon's facility at GCN to reproduce the throttle twist grip failure. The rubber shield from the collective was bent due to the operator's storage method, and tearing was noted adjacent to where the engagement notch would make contact when the throttle was in idle. Multiple attempts to engage the rubber shield and notch to prevent throttle manipulation from idle to flight were unsuccessful in causing jamming.
Operator's Procedural Changes
Following the accident and investigation, the operator implemented changes:
- No manipulations of the flight twist grip throttle would be done unless over a hard landing surface at an airport.
- All company instructors would be sent to the manufacturer's factory flight school for instructor training.