Piper PA28 N151DC accident near Okeechobee, Florida

Probable cause

The failure of the No. 3 piston due to fatigue cracking, which resulted in a total loss of engine power and subsequent forced landing, during which the airplane impacted obstacles.

NTSB analysis

The operator reported that the pilot was conducting a cross-country, solo instructional flight. When the airplane was about 3,000 ft mean sea level, the engine suddenly started running roughly accompanied by “abnormal” noises. The pilot attempted to troubleshoot the problem by performing the “engine roughness” checklist to no avail. About 10 seconds after completing the checklist, the engine lost all power. The pilot then established the best glide speed, chose a private grass strip for a forced landing, and conducted the “engine power loss in flight” checklist without success. Once committed to landing, he conducted the “power off landing checklist.” After the airplane touched down about halfway down the grass strip it skidded and subsequently impacted farm equipment and other obstacles, and it then came to rest against a building. The airplane sustained substantial damage to the fuselage and tail section, and the wings were sheared off.

Examination of the engine revealed that there was a hole in the crankcase above the No. 2 cylinder, consistent with a catastrophic engine failure, and that the No. 3 piston had failed. Metallurgical examination of the No. 3 piston revealed that two fatigue cracks had emanated from the outer face of a lubricating hole, which resulted in the piston failing, ancillary damage to the cylinder and engine, and a subsequent total loss of engine power. The areas outside of the fatigue crack regions and fracture faces exhibited a rough texture and on-slant planes consistent with overstress separation. The reason for the initiation and propagation of the fatigue cracks could not be determined. Even though the engine was 200 hours past the manufacturer’s recommended time before overhaul limit, it could not be determined if that contributed to the fatigue cracking.

Text from the NTSB. Open the NTSB docket for ERA16LA164 for the full record.