- Location: Wainwright, Alaska
- Accident Number: ANC23FA056
- Date & Time: July 20, 2023, 11:05 Local
- Registration: N311MH
- Aircraft: Bell 206-L4
- Aircraft Damage: Destroyed
- Defining Event: Controlled flight into terr/obj (CFIT)
- Injuries: 4 Fatal
- Flight Conducted Under: Part 135: Air taxi & commuter - Non-scheduled
https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/192675/pdf
https://data.ntsb.gov/Docket?ProjectID=192675
On July 20, 2023, about 1105 Alaska daylight time, a Bell 206L-4 helicopter, N311MH, was destroyed when it was involved in an accident near Wainwright, Alaska. The pilot and three passengers were fatally injured. The helicopter was operated by the pilot as a Title 14 Code of Federal Regulations Part 135 on-demand charter flight.
The helicopter pilot was under contract to the State of Alaska’s Department of Natural Resources (DNR) to transport scientific crews to various remote locations within the North Slope region. The accident flight departed on a visual flight rules flight from Utqiagvik, Alaska, with an anticipated brief stop at the Atqasuk airport, before continuing to remote sites to the east of Wainwright, Alaska, then returning to Utqiagvik. When the helicopter did not arrive back in Utqiagvik, search and rescue was dispatched to search for the missing helicopter.
The partially submerged, fragmented helicopter wreckage was found in the shallow waters of Lake Itinik, about 30 miles east of Wainwright. Lake Itinik was a large, oval-shaped arctic lake more than three miles wide in some areas. The terrain around the lake consisted of flat, featureless, arctic tundra-covered terrain.
Examination of the airframe and engine revealed no evidence of any preaccident mechanical failures or malfunctions that would have precluded normal operation.
Archived satellite tracking data indicated that the helicopter was flying about 88 ft above ground level (agl) at 93 knots shortly before impacting the water. Although there was a possibility of some overcast clouds and restricted visibility in fog/mist over the accident site, there were no observations or forecasts for any significant turbulence, low-level wind shear, convective activity, or icing over the area at the time of the accident. Another pilot in the area of the accident reported clear skies with no restriction to visibility, and weather camera images near the accident site also revealed no cloud coverage and unrestricted visibility.
Flight data from previous flights flown by the accident pilot revealed a pattern of high-speed, low-altitude flights similar to the flight profile of the accident flight.
The helicopter was being operated over water below the operator’s requirement of being within power-off gliding distance from shore.
The pilot’s decision to fly at a low altitude in flat light conditions, which obscured the features of the terrain, likely resulted in a loss of visual clues regarding the helicopter's distance from the ground. A flat, featureless lake offers little in the way of visual references for the pilot. Without terrain, landmarks, or other visual cues to help judge altitude and position, it's easy to become disoriented. This can be particularly dangerous when flying at low altitudes. The flat, reflective surface of the water can create a false horizon illusion, making it difficult for the pilot to accurately perceive the aircraft's attitude. Over a flat, featureless surface like a lake, depth perception can be impaired, making it difficult to judge the distance to the water and increasing the risk of flying too low or contacting the water.
Toxicology results indicated that the pilot had used the medication cetirizine. The measured cetirizine level in blood indicates a possibility that the pilot may have been experiencing some associated impairing effects, such as mild sedation, at the time of the accident. However the investigation was not able to determine what role, if any, the effects of the pilot’s cetirizine use may have had on his operation of the helicopter.
- Probable Cause: The pilot's decision to fly at a low altitude over a large body of water toward featureless terrain, which resulted in a loss of visual clues and controlled flight into terrain.
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