Accident Details
On August 2, 2021, at about 1458 Alaska daylight time, a Stinson 108-1 airplane, registration N8656K, was substantially damaged when it struck trees during takeoff near Sterling, Alaska. The private pilot and three passengers were not injured. The flight was conducted as a personal flight under Title 14 Code of Federal Regulations Part 91.
Pilot Report
The pilot reported that he was taking friends on a local flight. The airplane's useful load was 766 lbs, and he estimated the takeoff weight was less than 690 lbs, which included the passengers and about 120 lbs of fuel. The takeoff roll was longer than normal, but the airplane climbed normally with one notch of flaps until about 100 ft above ground level. At that point, the engine did not seem to be producing full power, the airplane would no longer climb, and it began descending toward trees off the departure end of the runway. The airplane impacted the trees and came to rest at an estimated 45° nose-down angle. Both wings and the fuselage sustained substantial damage.
Witness Video
A video taken by witnesses near the runway showed the airplane from the start of the takeoff roll until just before impact. The main landing gear became airborne just before the tailwheel, and the airplane entered a nose-high attitude, ascending to about treetop level. About 6 seconds after takeoff, the airplane began to descend in a nose-high attitude and continued until the recording stopped. The engine sound was consistent throughout the video with no audible anomalies. The windsock visible in the video indicated a slight right-quartering tailwind at the time of takeoff.
Engine Examination
Postaccident examination of the Franklin 150-B4 engine revealed that all bottom spark plug ignition wire caps were finger tight. The top spark plug from the No. 6 cylinder was also finger tight and exhibited signatures consistent with exposure to high heat on the outside of the plug. The crankshaft was manually rotated; cylinders were checked for suction and compression. The No. 2 and No. 3 cylinders showed weak compression and suction was difficult to detect. When the oil sump was removed, a small metal gear, a portion of a cotter pin, and pieces of metallic debris were found. The camshaft had scoring consistent with foreign debris. The fuel strainer contained organic material and debris within the screen and at the bottom of the bowl. The small metal gear was later determined to be from the original mechanical tachometer, which had fallen into the oil sump when the original tachometer was replaced with a digital tachometer.