CESSNA 185Copper Valley Air Service

The pilot was conducting a scheduled passenger flight in the single-engine airplane in day visual meteorological conditions. Recovered data from an onboard GPS unit revealed that, after reaching a GPS altitude of about 7,500 ft, the airplane flew on a southeast track for about 10 minutes with a groundspeed between 120 and 130 knots. About 2 minutes before the accident, the airplane initiated a gradual right turn to the south and began a descent that averaged about 734 ft per minute. The last fully recorded in-flight data point showed the airplane at a GPS altitude of 5,715 ft with a groundspeed of 154 kts. The distribution of the wreckage at the accident site indicated a high-speed, near vertical impact, with portions of the right wing and empennage scattered between 400 and 700 ft from the main wreckage, consistent with an in-flight breakup. Fractured areas of the right wing, the left deformation of the vertical stabilizer and rudder, and the fractured attach points were consistent with overload separation of the right wing, which caused the airplane to snap roll to the right, creating the necessary torsional forces to deform the vertical stabilizer and twist the empennage from the fuselage. Examinations on the engine and airframe did not reveal evidence of any pre-existing anomalies that would have precluded normal operation. Flight control continuity was established, and the propeller showed evidence of rotation at impact. All of the fractured surfaces exhibited a dull, grainy appearance consistent with overstress separation. There was no evidence of fatigue or corrosion noted on any of the areas examined. The reason for the overstress and subsequent in-flight breakup could not be determined based on the available information.