Incident Details
A pilot was assigned an aircraft equipped with a recently overhauled engine to tow a banner. During preflight checks, the pilot started and ran up the engine three times. On each occasion, the engine ran rough and lost revolutions per minute (RPM) during magneto checks. After each occurrence, company maintenance personnel cleaned the spark plugs and released the aircraft for flight.
Test Flight and Banner Engagement
The pilot conducted a test flight following the maintenance actions and reported that the engine performed normally. Subsequently, the pilot lowered the banner hook, dove to engage the banner, and began to climb. The engine then began to run rough and lost power. The pilot attempted to jettison the banner twice but was unable to do so. He then attempted to land on an intersecting runway, which resulted in a crash.
Engine Examination
An examination of the engine revealed that the spark plugs were oil fouled and wet. It was also found that the cylinders of the engine had just been installed, and there was no record of an engine run-in procedure being performed.