Accident Overview
On June 25, 2016, at approximately 1800 Alaska daylight time, a Stinson 108 airplane, registration N9063K, sustained substantial damage during a forced landing after a loss of engine power near Big Lake, Alaska. The aircraft was operated by the private pilot under Title 14 Code of Federal Regulations Part 91 as a visual flight rules flight. The flight had departed Merrill Field Airport in Anchorage, Alaska, around 1725 with three people on board: the pilot and two passengers. The pilot and one passenger suffered minor injuries, while the second passenger was uninjured. Visual meteorological conditions prevailed, and no flight plan was filed.
Flight and Loss of Power
The pilot stated that the flight was intended as a sightseeing trip for two visiting family members. Approximately 35 minutes after departure, while circling a friend's cabin at an altitude of about 550 feet above ground level, the engine began to sputter and subsequently experienced a total loss of power. The pilot executed a forced landing in an area densely populated with spruce and birch trees, during which the wings and fuselage sustained substantial damage.
Post-Accident Examination
On October 12, 2016, investigators from the National Transportation Safety Board (NTSB) and a Federal Aviation Administration (FAA) safety inspector examined the airframe and engine at Alaska Claims Services, Inc., in Wasilla, Alaska. The propeller remained attached to the engine crankshaft, and both blades exhibited aft bending with minimal torsional twisting. A detailed inspection of the Continental O-470R engine found no anomalies, contamination, or evidence of malfunction in any accessories. Cylinders, pistons, valve train, crankshaft, and other internal components were all without evidence of anomaly or malfunction. The engine was rotated by the propeller, and blue spark was observed on the top ignition leads.
Fuel System Modification
Examination revealed that the aircraft's wing fuel tanks had been modified with an additional section welded onto the factory tanks, featuring lightening holes drilled in the factory end. Each tank was placarded near the filler cap with "FUEL 80/87 MINIMUM GRADE 20 GALLONS," and the fuel selector inside the cockpit was placarded "18 GAL." No FAA form 337 (major repair and alteration) or logbook entry for this modification was found in the airplane's maintenance records.
Weather Conditions
The closest weather reporting facility was Wasilla Airport, approximately 19 miles east of the accident site. At 1756, the observation reported wind from 080 degrees at 4 knots, visibility 10 statute miles, few clouds at 4,600 feet, scattered clouds at 5,500 feet, broken clouds at 7,500 feet, temperature 66°F, dew point 48°F, and altimeter 29.89 inHg.
Additional Information
The pilot did not submit the required NTSB Pilot/Operator Accident Report form despite repeated attempts by investigators. The examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.