AO-1990-088

After flying over the top of Mt Mantell at a height of about 5500 feet, the pilot descended close to the mountainside intending to fly alongside a rugged rock face at an elevation of approx 4000 feet. At the bottom of the descent, he raised the collective lever to level out and heard the engine rpm increase abnormally. The pilot landed without delay. The helicopter rolled onto its left side on the rough sloping terrain.