An employee was preparing a commercial jet-liner to be repainted. He had accessed the wing via a scissor lift, and was standing on a flap over an aft wing box, at a height of approximately 15 feet. His harness was on, and he was hooked up to the scissor lift yoyo. He slipped off the top of the wing and fell approximately 6 feet, making contact with the plane and scissor lift, resulting in a fractured left femur.