On July 4, 1993, about 0840, a Cessna 150; N6097G, sustained substantial damage when it impacted the ground 3/4 miles east of Barnett Memorial Airport, Mt. Morris, Illinois. The pilot and passenger both received serious injuries. The flight was originating from Kenosha Municipal Airport, Kenosha, Wisconsin and was operating in visual meteorological conditions under 14 CFR Part 91. A pilot and witness, Richard Kluver, reported seeing N6097G directly in front of, but somewhat higher than himself while entering the landing pattern for Barnett Memorial Airport to the southwest of the runway 27. While Mr. Kluver was traveling east on the downwind leg, N6097G "swooped down into the pattern" into a position to the left and slightly behind Kluver, also on the downwind leg. Kluver reported hearing a voice on the radio say, "base to final Mt. Morris," when N6097G was even with the east end of the runway. Kluver saw the airplane make a sharp left turn and stated "the left wing tip 'stalled' and went downward, pivoting on the left wing tip, turning around 2-3 times." Then, just prior to impact with the ground, the pilot appeared to gain some control as both wings were level. The plane struck the ground at approximately a 45 degree angle, nose first. Several other witness accounts support Mr. Kluver's statement. Post accident examination revealed no evidence of pre-impact mechanical malfunction with the airframe, engine, or accessories.