The Twin Otter was carrying six barrels of Jet B fuel for a helicopter company to Markham Bay, an off-strip landing site. and touched down just after the threshold. The aircraft became airborne 18 m further on and bounced two times before touching down for the last time. The brakes were applied, but power was increased later in an attempt to takeoff again. The aircraft became airborne when the ground fell away beyond the runway and flew for 1000 feet before striking a rock with the main gear. The gear was sheared off and the Twin Otter stalled and crashed onto a rocky beach. CAUSES AND CONTRIBUTING FACTORS: “For unknown reasons, a decision was made to overshoot even though insufficient runway remained for acceleration, take-off, and climb. Likely contributing directly to the decision to overshoot was the difficulty in controlling the aircraft on touchdown.”