Primary finding
Probable cause
The pilot's inadequate visual lookout while lifting into a hover to ensure the helicopter was clear of all objects, which resulted in separation of an external mirror that then struck and damaged a main rotor blade. Factors in the accident were the presence of a seismic cable, and high vegetation around the helicopter's takeoff spot.
Investigator assessment
Analysis narrative
The commercial certificated helicopter pilot was conducting external load operations in support of seismic operations, and landed a high skid-equipped helicopter in a confined area to pick up a passenger. The landing area had knee to waist level brush. The pilot did not exit the helicopter, but waited until the passenger climbed aboard. The pilot reported that the passenger unknowingly drug a seismic cable over the toe of the left skid as he climbed into the helicopter. As the pilot was lifting the helicopter into a hover, 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. 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.
Source record
Factual narrative
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.