On April 28, 2013, about 1234 eastern daylight time, an Aeronca 11AC, N3503E, impacted the ground in a nose down attitude on a golf course near Hoosick Falls, New York. The commercial pilot sustained serious injuries. The airplane sustained substantial damage to the wings, firewall, and fuselage. The airplane was registered to and operated by a private individual under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed and no flight plan had been filed for the local flight that originated from the Chapin Field Airport (1B8), Cambridge, New York.According to several eyewitnesses, the airplane was observed flying overhead when some of the witnesses heard the airplane "throttle down" and then it appeared to be in a flat turn. One eyewitness stated that it appeared that the airplane "was flying sideways." Another eyewitness characterized it as a "large circular motion but kept losing altitude." Several witnesses also reported hearing the engine operating at an "idle" position the entire time. Several attempts to communicate with the pilot were unsuccessful; however, his spouse reported to the NTSB that her husband stated that the airplane "all of sudden would not respond to commands." Initial examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that the airplane came to rest in a nose down attitude at the edge of a golf course, about 100 yards from several homes. The right wing exhibited impact crush damage on the outboard one half and the left wing was separated from the fuselage at the aft wing attachment bracket. According to copies of the airplane's maintenance records, the most recent annual inspection was conducted on September 12, 2012. The recorded tachometer reading at that time was 1011.79 hours and the aircraft total time in service was 1684.33 total hours. The mechanic, that performed the inspection, noted that all inspections panels were opened and that all control cables, pulleys, attach fittings, hinges, and points were inspected and lubed. According to an FAA inspector, at the time of the accident, the airplane had 1702.33 hours total time in service and had operated about 18 hours since the most recent inspection. No entries were located, in the maintenance records provided, that indicated the brackets had ever been replaced or welded; a search of the NTSB database did not reveal any previous reported accidents for the accident airplane. The right and left wing aft attachment brackets, located on the trailing edge of the wing and attach the wing to the fuselage, were removed and sent to the NTSB Materials Laboratory in Washington, DC, for further examination. Each wing attach bracket consisted of two plates held into place by two cross members welded between them. One right wing attach bracket cross member was absent and not recovered, the other cross member remained attached to only one of the plates. Examination of the fracture surfaces revealed that the fractures were consistent with overstress. The left wing aft attachment brackets consisted primarily of a welded cluster of tubing. Examination revealed one of the tubes was bent out of position and a corresponding fracture occurred at the location where it joined the other tubes in the cluster. The cross members had separated from the plates leaving one attached to each plate. The deformation of the plates and the fracture surfaces were consistent with overstress. Further examination of the welds that connected the cross members to the plates, of both attachment brackets, appeared to lack full penetration into the base material.