On June 20, 1997, about 1600 Alaska daylight time, a wheel equipped Cessna 206 airplane, N756DJ, operated by Warbelow's Air Adventures as a scheduled commuter flight under 14 CFR Part 135, sustained substantial damage while descending to land at the Deadhorse Airport, Prudhoe Bay, Alaska. The solo airline transport pilot was not injured. The flight departed Nuiqsut, Alaska, and was en route to Prudhoe Bay. Visual meteorological conditions prevailed, and a VFR flight plan was filed. According to the operator, the pilot was flying a scheduled commuter flight route with cargo only aboard. When the pilot reduced engine power and begin to descend for a landing at the Deadhorse Airport, the aft cargo door opened and slammed against the side of the fuselage, resulting in substantial damage to the airframe. The pilot continued to Prudhoe Bay, and made an uneventful landing. The pilot wrote in his report to the NTSB that he thought he had latched and locked the door, but realized when the door opened that he had not secured it properly. Postaccident inspection of the airplane by FAA inspectors at Fairbanks, Alaska, disclosed damage to fuselage formers and stringers. The door latching mechanism was also examined and found to function satisfactorily, with no observed mechanical deficiencies.