On May 31, 2003, at 1640 central daylight time, a Grumman G-164B, N48597, piloted by a commercial pilot, sustained substantial damage during an uncontrolled descent into terrain while on a downwind departure from runway 14 (3,702 feet by 60 feet, asphalt) at the Superior Municipal Airport (12K), Superior, Nebraska. Visual meteorological conditions prevailed at the time of the accident. The pilot sustained serious injuries. The aerial application flight was operating under the provisions of 14 CFR Part 137 without a flight plan. The pilot reported departing runway 14 using about 1,000 feet of runway. The pilot noted that the liftoff was smooth and he established a 100-foot per minute climb. The pilot stated, "After crossing the approach end of runway 14 [,] I felt the tail push down and buffet. I thought that I had hit some bad air or something." The pilot reported the aircraft buffeted again and began an uncontrolled descent. The pilot further reported he lowered the nose of the aircraft to "avoid a stall and the aircraft just kept coming down." The pilot stated he dumped his load of water and increased his engine power. He noted, "normally the aircraft will pitch up as the load comes off. However I could not feel the load coming off even though I could see the shadow of the water on the ground." The pilot reported the aircraft continued the uncontrolled descent and impacted the ground with the tail impacting first, followed by the main landing gear. The aircraft nosed over. The pilot's total flight time in the accident make and model aircraft was less than one hour. The winds and temperatures reported by the weather observation facility at Blosser Municipal Airport (CNK), 35 miles to the southeast of the accident site, were: Observation time: 1555 Wind Direction: 150 Wind Speed: 7 knots Temperature: 22°C Observation time: 1655 Wind Direction: Variable Wind Speed: Light Temperature: 23°C Observation time: 1755 Wind Direction: 140 Wind Speed: 9 knots Temperature: 23°C The winds and temperatures reported by the weather observation facility at Hastings Municipal Airport (HSI), 38 miles to the northwest of the accident site, were: Observation time: 1553 Wind Direction: 130 Wind Speed: 8 knots Temperature: 23°C Observation time: 1653 Wind Direction: 120 Wind Speed: 7 knots Temperature: 22°C Observation time: 1753 Wind Direction: 120 Wind Speed: 9 knots Temperature: 23°C The pilot reported the winds were light and variable. The pilot also noted that he "spotted a small [whirlwind] in the grass along the side of the road as I was driving to the airport. I thought to myself that it was going to be a bumpy ride." The pilot further noted, "it is my opinion that I must have encountered a lateral wind shear and was unable to maintain flight in those conditions."