Cessna 152 N93441 accident near Moore, South Carolina

Probable cause

The certificated mechanic's improper installation of a helicoil, which resulted in the separation of a sparkplug and the helicoil and led to a partial loss of engine power.

NTSB analysis

The local instructional flight had departed from the airport about 30 minutes prior to the accident. After completing several aerial maneuvers, including slow flight and power-off stalls, the student pilot had begun a recovery from another power-off stall. When he applied throttle, the engine immediately began to run rough. The certificated flight instructor decided to perform a forced landing in a farm field. During the landing roll, the nosewheel came in contact with the soft soil and the airplane nosed over. A postaccident examination of the engine by a Federal Aviation Administration inspector revealed that the bottom sparkplug and associated helicoil on the No. 4 cylinder had separated from the cylinder. After new sparkplug and helicoil was installed in the engine, it ran normally.

The airplane's engine maintenance logbook showed that four days prior to the accident, the bottom sparkplug and helicoil had been replaced on the No. 4 cylinder due to a bad helicoil. The mechanic had installed a standard helicoil contrary to the engine manufacturer's recommendation to install oversize helicoil spark plug inserts.

Text from the NTSB. Open the NTSB docket for ERA10LA187 for the full record.