On December 24, 2012, about 1015 central standard time, an experimental amateur-built Swift II, N84NS, impacted terrain following a loss of control after takeoff from Twin-Oaks Airport (T94), San Antonio, Texas. The airplane sustained substantial damage. The pilot sustained serious injuries and the pilot rated passenger sustain minor injuries. The airplane was registered to and operated by the pilot under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed and a flight plan had not been filed for the local flight that was originating at the time of the accident.

The pilot stated that during takeoff on runway 30 (2,225 feet by 30 feet, turf), he rotated the airplane about 75-80 knots. The airplane experienced a normal climb until reaching about 50-75 feet above ground level, when the airplane "suddenly" pitched left and was unresponsive to control inputs. The pilot tried to flare the airplane and reduce engine power "just before" the airplane impacted the ground. The airplane also impacted fences and a shed.

According to a Federal Aviation Administration inspector, a witness stated that the airplane pitched up abnormally. The pilot had modified the wings, and the wing stall progression was from the wing tip to wing root. There was about 12 gallons of fuel in the left wing fuel. The pilot stated that he was unable to counteract the left roll. Examination of the airplane flight controls confirmed flight control continuity.