NTSB Factual Report

On November 22, 2011, at 1055 central standard time, a Cessna C-152, N6436P, sustained substantial damage during a forced landing to a field after a partial loss of power near the Princeton Municipal Airport (PNM), Princeton, Minnesota. The student pilot, the sole occupant, was not injured. The airplane was registered to Ascend Aviation LLC and was being operated by the student pilot as an instructional flight under the provisions of the 14 Code of Regulations Part 91. Visual meteorological conditions prevailed at the time of the accident. No flight plan was filed for the local training flight.

The student pilot reported that he and his instructor had completed an hour of dual instruction in the airplane just prior to the accident flight. After the dual instruction flight was completed, he departed on his solo instruction flight and conducted two takeoffs and landings without incident. During initial climb after the third takeoff at about 300 – 400 feet above the ground, he heard a loud “pop,” and the airplane started to vibrate severely and lose engine power. He executed a forced landing to a nearby field. The airplane landed hard and nosed over during the landing roll.

A Federal Aviation Administration airworthiness inspector examined the airplane. The examination revealed that the lower spark plug of the number two cylinder and its associated threaded insert were missing. The threads in the top portion of the spark plug hole were stripped and only the bottom three threads remained. No other engine anomalies were observed. The inspection of the airplane’s engine maintenance logbook indicated that on November 15, 2011, the number one and number two cylinders had threaded inserts installed in the lower spark plug holes.

NTSB Probable Cause

The inadequate installation of the threaded insert in the No. 2 cylinder spark plug hole by maintenance personnel, which resulted in a loss of engine power during initial climb.