HISTORY OF FLIGHTOn June 08, 2013, about 0935 mountain standard time, a Eurocopter EC 130 B4, N130PH, experienced an engine control malfunction while the pilot was performing practice autorotation maneuvers near Grand Canyon, Arizona. American Helicopters LLC owned the helicopter, and Papillion Grand Canyon Helicopters operated the helicopter under the provisions of 14 Code of Federal Regulations (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), Grand Canyon, about 0815, with a planned destination of Valle Airport (40G), Grand Canyon. Visual meteorological conditions prevailed, and no flight plan had been filed. 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 was conducting a simulated engine failure, which he 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 (agl), he began to roll in the throttle in an attempt to increase engine power. The throttle twist grip was seized, and he could not manipulate the control to increase the power. The CFI performed a full down autorotation, and the helicopter touched down on the dirt terrain. The helicopter's nose tipped downward and then it rocked back on the skids, which resulted in the main rotor blades severing the tailboom. The helicopter came to rest about 3 nautical miles northeast of the Valle Airport. ADDITIONAL INFORMATIONAs a result of this accident and the subsequent investigation, the operator made changes to their normal operation procedures. No manipulations of the flight twist grip throttle will be done unless it is over a hard landing surface, and at an airport. All company instructors are now being sent to the manufacturer's factory flight school for instructor training. TESTS AND RESEARCHAmerican Eurocopter personnel examined the collective components under the supervision of the Federal Aviation Administration (FAA) Rotorcraft Directorate. American Eurocopter submitted a written report, and the Rotorcraft Directorate inspector who observed the inspection concurred with the facts in the report; the full report is attached to the public docket for this accident. Findings of the examination revealed a number of abnormalities. The grab on the return coil spring in the pilot's twist grip control was found out of its notched seat on the tube assembly. This would make it more difficult to move the throttle twist grip into/out of FLIGHT from IDLE. Papillon maintenance personnel reported that; "The spring was removed during the disassembly of the control during the initial investigation with the FAA POI and American Eurocopter Tech Rep present in order to determine if there was any FOD material internally and to inspect the spring. The co-pilot's side torque tube rack teeth exhibited a small amount of foreign object damage (FOD) with respect to the collective pitch torque tube block. The co-pilots side electrical wiring harness (coming out of the bottom of the collective), exhibited a pinching type of damage on the harness, where the wire harness enters the center of the collective near the pinion teeth and index notch. The twist grip handle was heavily worn; the black powder coat paint was worn off. This was noted to be an indication that the pilot collective was stiff or harder to manipulate than it should have been. The examination of the collective components failed to reveal the cause of the collective twist grip failure and further examination of the components with the airframe was scheduled. On January 14, 2014, Investigators examined the helicopter and its components at the Papillon facility at GCN, in an attempt to reproduce the collective throttle twist grip failure. It was noted that the rubber shield coming out of the collective was bent as a result of the operator's method of storage. Also, there was noted tearing of the rubber shield adjacent to where the engagement notch would make contact if the throttle was in the idle position. Multiple attempts were made to try and engage the rubber shield, and the engagement notch to prevent the throttle manipulation from idle to flight. All attempts were unsuccessful to cause any jamming of the throttle.