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scheduled calibration of their test gauges had been accomplished The switch was installed in another aircraft, and during ground tests the pressure switch opened when the propeller was fully feathered. However, on two tests, the holding coil held the cockpit feathering switch "in" during the unfeathering cycle. A flight test revealed no discrepancies.
The feather pump and motor assembly could not be operated as a unit due to impact damage. The commutator was discolored by heat and had burned spots on it. One brush was stuck in a holder that had overheated; the holder was partially melted, and the brush spring had collapsed and lost tension. There was no external heat damage nor evidence of ground fire in the pump area. The pump was bench checked satisfactorily.
The right engine showed no signs of pre-accident damage or operational distress.
Both engines had been installed in N 616Z by the Zantop maintenance facilities at Ontario, California, and were released for flight on January 17, 1963. A test flight was performed on January 17, 1963, which included full feathering in flight, with no reported discrepancies. Both engines operated 227:51 hours time since overhaul (TSO) before the last flight. The mixture control arm on the left engine was replaced after 110:56 TSO, the right magneto of the left engine was replaced at 144:48 TSO, and a No. 2 check was performed in the aircraft at 147:38 during which time a No. 1 inspection was performed on the left engine. The left throttle linkage was adjusted by an unlicensed mechanic at this time. A ground check showed no discrepancies and the aircraft flew 65:53 without any reported engine problems after this maintenance. The aircraft records indicated that all maintenance was performed and signed off in accordance with company and FAA requirements. However, the investigators were not able to ascertain what person inspected the adjustment on the throttle linkage. The testimony of the maintenance personnel who performed the work during the engine runup and post runup adjustments indicated that there were no discrepancies on the engine when they completed their work. The engine runup after maintenance was documented and the form was signed off by the shift foreman.
The landing area at Thun Field was approximately 5,200 feet long and 3,420 feet of this area is a macadam surfaced runway 40 feet wide. The remainder of the landing area, approximately 800 feet on the north end of the runway and 1,000 feet on the south end, was rough graded soil containing gravel, rocks, stones, and sod. The runway lights consisted of two green lights on the runway edges, 660 feet down the runway from the approach end of runway 17 and 10 sets of white lights spaced 240 feet apart, along the runway. The parallel rows of lights were 49 feet apart. A number of these runway lights were missing or inoperative at the time of the accident. There was a rotating white beacon installed and operating at Thun Field. The remaining portion of the landing area was not lighted. According to a Federal Aviation Agency survey performed October 3, 1962, there are tall trees in the approach zone which reduce the useable length of the hard surfaced runway to 2,667 feet.
Approximately 1,000 feet east of and nearly parallel to the runway is a bright lighted "drag strip" which is estimated to be 5,000 feet long and 90 feet wide. The drag strip looks very much like a lighted runway.
The FAA Radar Approach Control (RAPCON) chief testified that information taken from the State of Washington Directory of Airports was used to compile the data regarding Thun Field. This directory showed Thun Field's runway to be 5,300 feet long (3,500 feet asphalt) and 150 feet wide, elevation 520 feet, and a rotating beacon lighted all night. The Directory noted that 40-foot trees created an obstruction on
