Eurocopter AS350 N910S accident near Odanah, Wisconsin

Probable cause

The pilot's loss of helicopter control for undetermined reasons.

NTSB analysis

The pilot was on a scheduled pipeline patrol observation flight in a turboshaft-powered helicopter. When the pilot did not arrive at his destination, an alert notice was issued for the overdue helicopter. The helicopter wreckage was located about 22 miles west of the helicopter's departure point in a remote wooded area that was about 200 yards north of the east-west pipeline. The pilot was not in contact with air traffic control during the flight, and there was no record of a distress call. A witness working on the pipeline about 2 to 3 miles from the accident site, reported seeing the helicopter fly overhead and further reported that the helicopter looked and sounded "normal."

Visual meteorological conditions surrounded the area of the accident with 10 miles visibility and an overcast sky at 1,600 ft.

The post-crash fire consumed most of the cabin area, which limited the scope of the airframe and engine examinations. Additionally, fire damage prevented the retrieval of information from the helicopter's cockpit image and flight data monitoring system, including nonvolatile memory from the digital engine control unit and engine data recorder. However, no preimpact abnormalities were noted during the engine or airframe examinations. Further, the engine's intake axial compressor blades exhibited damage near the outer tips, and the module 5 torque nut had a slippage of about 1/16 to 1/8 inch, (2 to 4 millimeters) consistent with the engine producing power at the time of impact.

The pilot's autopsy noted moderate-to-severe coronary artery disease, scarring of the heart muscle from a previous myocardial infarction (heart attack), and changes in the blood vessels of the liver that were indicative of congestive heart failure. Thus, the pilot would have been at an increased risk for an acute coronary event causing symptoms such as shortness of breath, chest pain, palpitations, or fainting. The pilot's complete medical history was not available, and a determination of medical impairment or incapacitation could not be made based on the available evidence for the accident.

Text from the NTSB. Open the NTSB docket for CEN19FA018 for the full record.