Eurocopter EC 130 B4 N130PH accident near Grand Canyon, Arizona

Probable cause

A loss of throttle control movement during a practice autorotation that was planned to terminate with a power recovery for reasons that could not be determined because postaccident examination did not reveal any anomalies that would have precluded normal operation. Contributing to the accident was the soft terrain, which resulted in the skid getting caught, the nose-down movement of the helicopter, and subsequent main rotor contact with the tailboom.

NTSB analysis

The purpose of the flight was for the flight instructor to train a newly hired pilot in the company's normal operating procedures. After performing numerous autorotation maneuvers, the flight instructor rolled the throttle twist grip to the "idle positon" to conduct a simulated engine failure and autorotation, which he intended to terminate with a power recovery. After configuring the helicopter for an appropriate airspeed and while descending through 200 ft above ground level, he attempted to roll the twist grip from the "idle" to the "flight" position to increase engine power; however, he was not able to roll the twist grip at all. The flight instructor continued the autorotation to landing, and the helicopter touched down on soft terrain. A skid then got caught in the soft terrain, which resulted in the nose-down movement of the helicopter and the main rotor blades severing the tailboom. Postaccident examinations of the collective system revealed some anomalies; however, none of the anomalies would have resulted in the loss of throttle control movement.

If the landing had been made on a hard surface, it is unlikely that the skid would have gotten caught. Following the accident, the operator changed its procedures to require that the manipulation of the throttle twist grip only be done over a hard landing surface and at an airport.

Text from the NTSB. Open the NTSB docket for WPR13LA266 for the full record.