Primary finding
Probable cause
The separation of a spark plug and 4 other spark plugs being 'finger' tight as a result of undertorquing by maintenance personnel when they were reinstalled following inspection. A factor was a lack of suitable terrain for the forced landing.
Investigator assessment
Analysis narrative
The pilot reported that shortly after takeoff, the airplane's engine 'stopped and then started up again.' Soon after, the engine started to lose power again. A forced landing was made. When the aircraft was inspected, it was found that one of the spark plugs in each of the number 1, 4, 5, and 6 cylinders were 'finger' tight, and the second spark plug in the number 6 cylinder had completely separated from the cylinder. These plugs were removed by a mechanic for the pre-buy inspection prior to the pilots purchase of the airplane.
Source record
Factual narrative
On December 28, 1995, at 1600 central standard time, a Republic Seabee RC 3, N6127K, was substantially damaged while performing a forced landing near Whitewright, Texas. The aircraft was being operated by the owner, under Title 14 CFR Part 91. The flight originated from Tri-County Airport located near Whitewright, Texas, at approximately 1550. Visual meteorological conditions prevailed for the ferry flight and no flight plan was filed. The pilot had purchased the airplane near Atlanta, Georgia and was ferrying it to Chandler, Arizona. The pilot reported he had a mechanic perform a pre-buy inspection before purchasing the airplane which included removal and inspection of the spark plugs. He had stopped at Tri-County Airport for fuel and oil (the airplane was using 1 1/4 quarts of oil per hour). Shortly after takeoff, the airplane's engine "stopped and then started up again." Soon after, the engine started to lose power again. During the ensuing forced landing on a road, the airplane impacted road signs and one wing separated from the fuselage. Inspection of the airplane revealed that one spark plug on each of number 1, 4, 5, and 6 cylinders was "finger" tight. The second spark plug on the number 6 cylinder had completely separated from the cylinder. The inspection also revealed the engine was covered in oil. -