Departure and Witness Reports
The cross-country flight originated from Big Bear, California, with stops in Las Vegas, Nevada, and Grand Canyon, Arizona, before returning to Big Bear. The accident occurred during takeoff from runway 03 at Grand Canyon National Park Airport. Runway 03 is 8,999 feet long with a 0.8 percent up gradient (76-foot increase) and a density altitude of 8,800 feet mean sea level. Witnesses reported that the airplane appeared to be slow and barely cleared trees and buildings while climbing into mildly rising terrain. About 2 miles from the runway, the airplane was seen to roll to the left and descend into trees.
Performance Documentation
The FAA Approved Flight Manual (AFM) for the accident airplane and associated performance data were not found at the accident site. However, a Cessna 337 Skymaster AFM was recovered. Additionally, a California Airport Directory was found, but no Grand Canyon Airport information was present other than the airport information on the Las Vegas Sectional Chart.
Magneto and Spark Plug Examination
Examination of the dual magneto revealed internal case corrosion on the left interior of the magneto. The right magneto was timed at 22 degrees before top center (BTC) instead of the specified 25 degrees BTC. Test bench results indicated that the right magneto exhibited a weak spark. The massive electrode spark plugs had gaps exceeding the recommended maximum gap. Cylinder plugs No. 1 and 2 were fuel sooted, No. 3 appeared lean, and No. 4 was slightly sooted.