Hughes OH-6A N4191A accident near Monroe, North Carolina

Probable cause

The pilot-rated-passenger’s failure to maintain clearance from a known wire hazard during low-level maneuvering. Contributing to the accident was the pilot-in-command’s inadequate monitoring of the flight.

NTSB analysis

During a flight to "simulate a mission" to examine power lines, the helicopter had been paralleling the west side of transmission lines. While resetting the global position system (GPS), the pilot-in-command (PIC) transferred controls to the pilot-rated-passenger. While the PIC was trying to reduce the sensitivity of the GPS warning system, the helicopter made a right turn of almost 260 degrees of heading change, allowing the helicopter to be on a perpendicular ground track and traveling directly toward the power lines. The helicopter collided with the topmost lines in the set, which were the grounding wires for the transmission line. The helicopter was observed by an eyewitness impacting the power line and descending to the ground. Examination of the wreckage revealed no evidence of any mechanical deficiencies. Several witnesses heard the helicopter and reported that it sounded normal prior to impacting the power lines. The main rotor blade was separated from the main wreckage. The pilot-rated-passenger had a history that he had not revealed to the Federal Aviation Administration of kidney stones, severe knee pain, and regular use of prescription pain medication. This pilot had seen an orthopedic surgeon the day before the accident for continuing knee pain, for which he had requested and received additional pain medication "to help him sleep." Toxicological testing was consistent with the recent use of the potentially impairing narcotic medication that had been prescribed the day before the accident. It is possible that the pilot-rated-passenger was impaired or distracted by knee pain, by the use of narcotic medication for that pain, or by fatigue due to insomnia from the knee pain; however, the investigation could not conclusively determine if impairment or distractions contributed to the accident.

Text from the NTSB. Open the NTSB docket for ERA09LA139 for the full record.