NTSB Identification: ANC12FA006
Nonscheduled 14 CFR Part 135: Air Taxi & Commuter
Accident occurred Saturday, October 29, 2011 in Iliamna, AK
Probable Cause Approval Date: 02/13/2014
Aircraft: EUROCOPTER AS 350 B2, registration: N165EH
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The helicopter pilot was under contract to support an aerial seismic survey project in a remote part of western Alaska. The survey crew had completed their survey, and the pilot, who was the only occupant, was relocating the helicopter to the operator's base in south central Alaska; however, poor weather conditions delayed his departure until mid-afternoon on the fourth day. The pilot made two fuel stops while en route, and both fuel vendors noted that the pilot seemed rushed and that he mentioned that he was trying to get to his destination before dark. The operator reported the helicopter overdue when the helicopter failed to arrive and they were unable to make contact with the pilot. Searchers discovered the fragmented wreckage about 7 miles southwest of the destination airport, in an area of marshy, tundra-covered terrain.

Dark night visual meteorological conditions prevailed at the destination airport before the accident, and transient snow showers and reduced visibility were reported in the area just after the accident. Examination of the helicopter and engine revealed no preaccident mechanical anomalies that would have precluded normal operation. The debris path and extensive fuselage fragmentation were consistent with the helicopter impacting terrain at high speed.
The pilot's autopsy revealed several heart abnormalities, including an enlarged heart, a 90-percent occlusion of the left anterior descending coronary artery, a 99-percent occlusion of the right coronary artery, and an aortic valve that was severely calcified and stenotic. Such findings would have put the pilot at high risk of a sudden cardiac event, including acute myocardial infarction, syncope, or arrhythmia, any of which would have impaired or incapacitated him. Further, the weather and the pilot's rush to reach his destination by nightfall after a 4-day delay may have contributed to the pilot's stress level, increasing the risk that his severe but undiagnosed heart disease would cause an acute medical event during the flight.

Given the lack of mechanical deficiencies that would have precluded normal operation of the helicopter, and the pilot's severe coronary artery disease and aortic stenosis, it is likely that the pilot's medical conditions caused sudden impairment or incapacitation, which resulted in the loss of control of the helicopter. Although it is possible that the pilot did not recognize that he was flying the helicopter in a shallow descent into terrain, the overwhelming evidence of heart disease compounded by stress makes it more likely that the pilot was impaired or incapacitated.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The pilot's loss of control due to sudden medical impairment or incapacitation.

Full narrative available

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