On August 26, 1996, about 1115 hours local Guam standard time, a Bell 47-G4A, N474GA, was destroyed during a banner towing operation at Apra Harbor, Guam. The pilot was fatally injured. Visual meteorological conditions prevailed for the local area flight. The flight originated from a helipad at Tamuning, Guam, at 1030. According to witnesses, the helicopter was towing a banner about 200 feet msl at 30 to 35 miles per hour. Everything appeared to be normal until the banner fell free from the helicopter. At that point, the helicopter started to rotate to the right and descend. The banner entered the water before the helicopter. The helicopter continued rotating to the right until it impacted the waters of Apra Harbor. According to an FAA inspector on scene during the recovery, the retaining nut for the universal joint to yoke on the tail rotor drive was not engaged but retained the safety wire. The safety wire was broken on the last twist prior to entering the universal joint's affixing hole. The solid drive pin located in the aft universal joint and through the drive shaft was missing.