NTSB Factual Report

On May 22, 2004, about 1605 Alaska daylight time, a Piper PA-31-350 airplane, N4105D, sustained substantial damage when it encountered severe turbulence while in cruise flight, about 5 miles west of Goodnews, Alaska. The airplane was being operated as a visual flight rules (VFR) cross-country positioning flight under Title 14, CFR Part 91, when the accident occurred. The airplane was operated by Grant Aviation Inc., Anchorage, Alaska. The airline transport certificated pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed, and VFR company flight following procedures were in effect. The flight originated at the Goodnews Airport at 1600, and was en route to Bethel, Alaska.

During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on June 2, 2004, the director of operations for the operator reported that the pilot was returning to Bethel without any passengers or cargo after delivering mail to Goodnews, which is located on the coast of the Bering Sea. When the pilot arrived in Bethel, he informed the director of maintenance that during the flight, the airplane encountered turbulence and the appeared to have received damage to the wings.

On June 3, the director of maintenance reported that the airplane received structural damage that consisted of wrinkling and rippling of both of the upper wing surfaces, extending about 8 feet outboard from each engine nacelle. In addition, the elevator had wrinkling that extended about 6 inches inboard from each of the outboard hinge attach points. Due to the damage, the company removed the airplane from service.

During a telephone conversation with the NTSB IIC on June 3, the pilot reported that during his flight to Goodnews, the wind conditions were about 070 degrees magnetic at 25 knots, with gusts to 30 knots, and the airplane encountered turbulence over an area of low hills that are north of the airport. When the pilot departed on the accident flight, he said he utilized runway 05 and began a right turn over the bay. He initially climbed the airplane to about 1,200 feet, but as he approached an area of low hills west of the airport, he descended to about 700 feet. At an indicated airspeed of about 185 knots, the pilot said that the airplane encountered severe turbulence for about 30 seconds, during which his radio headset was dislodged. He continued toward the coast and then turned northbound toward Bethel. After arrival in Bethel, he noticed the damaged wing surfaces.

The closest official weather observation station is Cape Newenham Long Range Radar Station, which is located about 32 nautical miles south of the accident site. At 1555, an automated weather observation system (AWOS) was reporting in part: Wind, 110 degrees (true) at 17 knots, gusts to 27 knots; visibility, 7 statute miles; clouds and sky condition, 1,200 feet overcast; temperature, 52 degrees F; dew point, 46 degrees F; altimeter, 29.76 inHg.

NTSB Probable Cause

The pilot's inadequate weather evaluation which resulted in an in-flight encounter with severe turbulence, and his exceedence of the design stress limits resulting in overstress of the wings. A factor contributing to the accident was the presence of turbulence.