The pilot was flying the ultralight vehicle to check it out before allowing his student to solo. Approximately 15 minutes after the pilot took off, he was flying over the airport at about 400 feet AGL when witnesses heard a 'loud non-metallic' sound from the vehicle. At about that time, it entered a left descending turn. Reportedly, the vehicle made about 3 turns, and during each turn, the bank angle increased. At approximately 200 feet AGL, the pilot released his parachute, but the canopy never blossomed. The vehicle impacted in a left wing down, nose low attitude. An exam revealed that the right wing fabric was torn in a manner that was consistent with an in-flight separation. The outboard compression support tube was found 15 feet from the main wreckage. Only remnants of the attach bolt were found. For vehicles manufactured after October 1983, the company had changed the grade of the bolt, but had not issued a service bulletin. However, a service bulletin, ALL-8303-A, was issued concerning loosening of coarse thread bolts (similar to the attach bolt) but no evidence of compliance was found.