At approximately 12:15 mountain time, a Cessna 425 crashed about two miles north of Fanning Field. The two occupants on board for the maintenance test flight were killed. The aircraft had recently had maintenance work performed on its autofeather system after reports of the left engine not autofeathering properly in flight. The maintenance work was performed and the purpose of the accident flight was to verify proper inflight operation of the system. Two witnesses described the aircraft as entering a spiral from a banked turn about five minutes after takeoff. One said he first observed the aircraft flying south 200 to 300 feet agl. He said the aircraft entered a left turn and began a skidding or sliding motion. It entered a spiral about 1 second later and crashed. The cockpit autofeather switch was found in the OFF position and both propeller levers were found full forward. All four blades of the detached left propeller appeared to be feathered.