On September 20, 2007, around 1600 eastern daylight time, an experimental amateur-built Siebert RV-9A, N3653, owned and piloted by a private pilot, was substantially damaged when it impacted terrain shortly after takeoff from a private airstrip near Barton City, Michigan. Visual meteorological conditions prevailed at the time of the accident. The personal flight was operating under the provisions of 14 Code of Federal Regulations (CFR) Part 91 without a flight plan. The pilot and passenger sustained serious injuries. The local flight was originating at the time of the accident. The airplane departed to the northwest from a private grass airstrip situated behind the pilot's residence. The northwest/southeast airstrip was about 1,160 feet long. The passenger reported that shortly after takeoff the airplane encountered a large wind gust that pushed the airplane to the left (southwest). After encountering a second wind gust, the airplane banked sharply and then descended vertically into trees and terrain. The passenger recalled that the airstrip's windsock did not indicate that there was significant wind prior to the accident flight. The pilot had no recollection of the accident flight. A weather observation station located about 16 nm south-southeast of the accident site reported the wind was from the east at 5 knots with no gusts. Another weather observation station located about 23 nm west of the accident site reported the wind was from the west-southwest at 4 knots, gusting to 10 knots.