CHI96LA287

While conducting aerial spraying over rolling terrain, the pilot experienced a violent nose down motion of the airplane, followed by the airplane going into a left wing down attitude. He recovered from the left wing down attitude, but experienced a right wing and nose down situation. The airplane struck the rolling terrain with the right wing, which subsequently resulted in extensive damage. The pilot reported no mechanical deficiencies or operational problems prior to impact. He believed that he may have encountered a windshear condition. About 21 miles west (at North Platte), the wind was from 180 degrees at 10 gusting 17 knots.

On August 9, 1996, at 1200 central daylight time (cdt), a Grumman-Schweizer G-164B, N6966K, registered to Wallace Flying Service, Inc., of Wallace, Nebraska, piloted by a commercial pilot, impacted terrain, while maneuvering during the aerial application of a herbicide. The airplane was destroyed. The pilot reported no injuries. The local CFR Part 137 flight was operating in visual meteorological conditions. No flight plan was on file. The flight originated from Wallace, Nebraska, at 1150 cdt.

According to the pilot's written statement, after making six agriculture spraying passes over rolling terrain, the pilot turned downwind over trees and experienced a violent nose down followed by a left wing down. He recovered from the left wing down and experienced a right wing down and nose down attitude. The airplane struck the terrain with the right wing.

A Federal Aviation Administration Principal Maintenance Inspector (PMI) represented the NTSB on-scene. The PMI said the pilot reported no mechanical deficiencies or operational problems prior to impact. The pilot believes he may have experienced a severe wind shear condition.