Rocksprings

The pilot was cleared to 17,000 feet approximately 7 minutes after takeoff. After arriving at 17,000 feet, radar showed the airplane in a meandering flight path increasingly off course that continued through the end of the flight, even after several prompts from the controller. The pilot was cleared to flight level 240 (24,000 feet) after about 6 minutes at 17,000 feet, and about 2 minutes later, while passing through about 18,000 feet, he made his last radio transmission, acknowledging a corrected heading. About 6 minutes later, the airplane arrived at 24,000 feet and the pilot did not make any intelligible responses to controller inquiries for the remainder of the flight. At 1456, radar showed the airplane in a descent to 21,000 feet before beginning a rapid descent and continuing to impact. The airplane was substantially damaged by the impact forces and the pilot, who was the only occupant, was fatally injured. During the review of the air traffic control recordings, it was determined that none of the voice transmissions from N43KM sounded as if the pilot was speaking through an oxygen mask microphone. At the accident scene both bleed air switches were observed to be in the closed position and the airplane pressurization switch on the console was observed to be in the dump position. No other preimpact anomalies were observed that would have prevented the normal operation of the airplane.

The 2,212-hour instrument rated commercial pilot collided with terrain while circling to land after completing an instrument approach to an uncontrolled non-towered airport. The airport had two instrument approaches to Runway 14; a VOR and a RNAV(GPS). The published minimums for a circling approach to Runway 32 are a 500 foot ceiling and one mile visibility (VOR14) and a 700 foot ceiling and one mile visibility for RNAV(GPS) to Runway 14. The weather at the airport at the time of the accident was reported as 300 overcast, visibility of 3/4 of a mile in mist, with winds from 020 degrees at 10 knots gusting to 14 knots. Two witnesses reported that the airplane circled over the airport and then descended straight to the ground. Radar data revealed that after the airplane made the instrument approach to Runway 14, at approximately 2,800 feet mean sea level (msl), the airplane initiated a circling turn to the left and a slight descent. The last radar hit showed the airplane at 2,600 feet at a groundspeed of 186 knots. A post impact fire consumed some of the airframe. The pilot's logbooks were not located during the course of the investigation and his instrument experience and currency could not be determined. The pilot was reported to be very familiar with the airport and the 2 instrument approaches. A detailed examination of the wreckage of the airplane failed to reveal any anomalies with the airframe, structure, or systems. Flight control continuity was established at the accident site. The engines were examined, and no mechanical anomalies were found. The propellers were shipped to the manufacturer's facility for examination and teardown. Both propellers were rotating at the time of ground impact. Neither of the two propellers was found in the feathered position. Blade damage was consistent with both propellers operating under power at the time of impact. No mechanical defects were noted with either propeller.

As the aircraft was climbing thru 14,800 feet for 19,000 feet, the pilot reported a rapid decompression. Two minutes later, he reported that he has lost the tail. Aircraft impacted in an inverted flat spin and the tail and a section of empennage were found about 3/4 mile away from main wreckage. Investigation revealed that a skin seam had split open along a 54' span in an area where 2 pieces of 'l' shaped channel had been riveted together to form a stringer. Normally the stringer would be made using a single piece of 't' shaped channel. The non-standard stringer had been fabricated during repairs made on the aircraft following a gear up landing 7 years prior to this accident. Analysis revealed that the rivets holding the 'l' channels together and failed in fatigue due to tensile cyclic loading whenever the aircraft was pressurized. Aircraft had a history of pressurization problems following the repair that was not properly performed or inspected. The pi1lot, sole on board, was killed.