On March 31, 2003, about 1000 Alaska standard time, a Hughes 369D helicopter, N90431, sustained substantial damage when a main rotor blade and the vertical stabilizer were struck by a severed external load mirror as the helicopter was lifting into a hover, about 7 miles southwest of Tyonek, Alaska. The helicopter was being operated as a visual flight rules (VFR) external load operation under Title 14, CFR Part 133, when the accident occurred. The helicopter was operated by Prism Helicopters Inc., Wasilla, Alaska. The commercial certificated pilot, and the sole passenger, were not injured. Visual meteorological conditions prevailed, and VFR company flight following procedures were in effect.

During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on April 4, the director of operations for the operator reported the pilot was lifting the helicopter into a hover in support of seismic operations. The director of operations said that as the pilot lifted off out of a confined area, he was not aware that the seismic cable was caught on the front toe of the left landing gear skid tube. As the helicopter gained altitude, the cable slid aft into the helicopter's external load mirror. The cable severed the mirror from the helicopter, and the mirror was propelled upward, into the main rotor blades. The mirror then struck the vertical stabilizer.

In the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1) submitted by the pilot, the pilot indicated that he landed the high skid-equipped helicopter in an area of knee to waist level brush to pick up the passenger. The pilot did not exit the helicopter, but waited until the passenger climbed aboard. The pilot reported that the passenger "apparently drug the seismic cable (black, less than 1 centimeter diameter) over toe of skid, unbeknownst to either the pilot or passenger."

A postaccident examination of the rotor system revealed that one rotor blade sustained a dent on the underside of the blade. The director of operations stated that the damaged blade was beyond allowable repair limits, and had to be replaced.

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