RANS S6ES N623LB accident near Elverta, California

Probable cause

A loss of engine power during initial climb due to a failed piston ring.

NTSB analysis

The student pilot reported that, shortly after takeoff for his practical test for a sport pilot certificate, when the airplane was about 100 ft above ground level, the engine lost power. He then began an emergency descent to a nearby field. During the landing, the airplane collided with a dirt berm and subsequently nosed over.

Postaccident examination of the engine revealed damage to both the forward and aft cylinder assemblies. The aft cylinder assembly's top piston ring was missing, and damage was noted to the associated ring land groove and piston. The lower piston ring was in place; however, the piston ring was distorted and jammed in its corresponding ring land groove. Mechanical-type damage was noted on the internal cylinder domes and piston faces of both the forward and aft cylinder assemblies, and the damage was consistent with pieces of the broken piston ring contacting the cylinder domes. The reason for the piston ring failure could not be determined. Postaccident review of the airplane's maintenance records revealed multiple entries outlining repairs to both the forward and aft cylinder assemblies; most of the repairs were associated with piston ring anomalies. One maintenance log entry indicated that the both the forward and aft cylinder assemblies' piston rings were replaced and that the cylinders were resurfaced due to "overheat damage."

Text from the NTSB. Open the NTSB docket for WPR12LA437 for the full record.