CHUIT RIVER, AK, USA
N4604Y
BELL 206B
THE PILOT LANDED ON A GRAVEL BAR IN A RIVER WHICH HAD HIGH BANKS. THE WIND WAS VARIABLE DURING THE APPROACH AND LANDING. HE 'PICKED' THE HELICOPTER BACK UP TO A HOVER TO REPOSITION ON THE GRAVEL BAR AND THE HELICOPTER BEGAN TO TURN TO THE RIGHT. HE APPLIED LEFT PEDAL, FELT A RESPONSE, BUT WAS UNABLE TO STOP THE TURN. DURING THE TURN THE HELICOPTER DESCENDED AND STRUCK THE WATER. AFTER EVERYONE EXITED THE HELICOPTER, IT ROLLED OVER AND SANK IN THE RIVER. ACCORDING TO THE MANUFACTURER AND THE FAA, WHEN A HELICOPTER IS OPERATING AT OR NEAR ITS MAXIMUM GROSS WEIGHT, TAIL ROTOR CONTROL MAY BECOME MARGINAL DEPENDING ON WIND CONDITIONS. HOVERING WITH A TAILWIND MAY CAUSE TEMPORARY LOSS OF TAIL ROTOR EFFECTIVENESS AND ALLOW THE HELICOPTER TO ROTATE ABOUT ITS VERTICAL AXIS. THE PURPOSE OF THE FLIGHT WAS FISH GUIDING.
On August 9, 1994, at 1230 Alaska daylight time, a skid equipped Bell 206B helicopter, registered to and operated by the pilot, crashed into the Chuit River. The business flight, operating under 14 CFR Part 91 for the purpose of fish guiding, departed the Anchorage, Alaska area and the destination was the Chuit River, 1 mile upstream from the mouth. Visual meteorological conditions prevailed and no flight plan was filed. The pilot and the four passengers were not injured and the helicopter rolled over and sank in the river. According to the pilot, the wind was variable during his approach and landing. The gravel bar on which he landed was not level so he picked the helicopter back up to a hover to move to a more level location. The helicopter immediately made a turn to the right. He applied left pedal and could feel a response but was unable to stop the rotation before the helicopter struck the water. The helicopter came to rest upright in the river. Everyone exited the helicopter and it rolled over and sank in the river. According to Bell Helicopter and the FAA, when a helicopter is operating at or near its maximum gross weight, tail rotor control may become marginal depending on wind conditions. Hovering with a tailwind may cause temporary loss of tail rotor effectiveness and allow the helicopter to rotate about its vertical axis. The pilot's flight time was provided by the FAA and came from his Application for Airman Certificate dated 9/24/92.
THE PILOT'S FAILURE TO MAINTAIN TAIL ROTOR EFFECTIVENESS DURING HOVER.
Source: NTSB Aviation Accident Database
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