On September 7, 2003, at 1028 eastern daylight time, a Cessna 180D amphibian, N6445X, was substantially damaged while departing from Moosehead Lake, Greenville, Maine. The certificated flight instructor and private pilot received minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight conducted under 14 CFR Part 91. According to the pilot, he was providing the private pilot a refresher course in seaplane flying. While conducting the fifth takeoff of the day, with the private pilot at the controls, the private pilot observed that he had no aileron control as the airplane lifted off from the lake. After the flight instructor assumed the controls, the airplane rolled to the right, impacted the water, and sank to a depth of 60 feet. A Federal Aviation Administration inspector examined the wreckage after the accident. He observed substantial damage to the left and right wings, and the fuselage. The inspector also observed that a turnbuckle was separated from the right aileron cable. The turnbuckle was not safety-wired. The airplane had accumulated about 55 hours of operation since it's last annual inspection. Examination of the airplane's engine maintenance logs revealed an entry that stated, "Removed and replaced left and right aileron control cables, 0752015-22. Replace aileron carry thru cable, 0510105-12, IAW Chapter 6-6-18 A,B,C. Rigged IAW par 6-20 A, thru I." The entry was signed and acknowledged, "I certify this Aircraft has been inspected I/A/W an annual inspection and determined to be in an airworthy condition."