Incident Overview
On September 21, 2010, at approximately 0940 Pacific daylight time, a Mooney M20C (registration N6090Q) experienced a partial loss of engine power during takeoff from Visalia Municipal Airport in Visalia, California. The commercial pilot, who owned, operated, and maintained the aircraft, was conducting a personal flight under visual meteorological conditions in accordance with 14 Code of Federal Regulations Part 91. No flight plan was filed. The pilot reported no injuries.
Sequence of Events
According to the pilot, the engine run-up performed prior to takeoff revealed no anomalies. Full engine power was applied and the takeoff commenced. At an altitude of approximately 300 feet above the runway, a loud pop was heard, and engine rpm dropped to 1,500. Unable to maintain flight, the pilot initiated a course reversal turn with the intention of making a forced landing back on the airport. However, the airplane's altitude proved insufficient to complete the turn, and it struck the ground adjacent to the departure runway.
Damage and Examination
The impact was severe enough to activate the emergency locator transmitter, break off the nose landing gear, and bend the outboard 6 feet of the right wing. The aircraft was substantially damaged.
Federal Aviation Administration (FAA) personnel later examined the Lycoming engine. They found that the bottom spark plug of the number three cylinder had blown out of its cylinder. The spark plug had been installed with a Heli-Coil insert, which surrounds the plug's threads in the cylinder. The blown-out spark plug appeared to have failed due to wear from repeated insertions and removals, which gradually loosened the Heli-Coil. FAA personnel stated that the spark plug had not been loose in the cylinder; rather, the Heli-Coil showed evidence of loosening over time. They further opined that signs of the Heli-Coil loosening would not necessarily have been apparent to a mechanic during routine maintenance.
Maintenance History
The engine had accumulated over 1,600 hours of total time since its last major overhaul. According to maintenance records, the number three cylinder had not been replaced since it was overhauled in 1987.