Piper PA28 N4298V accident near Lagrange, Georgia

Probable cause

Improper manufacture of a cylinder exhaust valve guide by the engine manufacturer, which resulted in a stuck exhaust valve and a partial loss of engine power during initial climb.

NTSB analysis

The flight instructor and student pilot had completed maneuvers over the local area before the student pilot performed a touch-and-go landing. During initial climb after the touch-and-go landing, about 200 to 300 ft above ground level, the engine began to run rough and the airplane stopped climbing. The flight instructor then took control of the airplane from the student pilot and made a right turn for a forced landing on a perpendicular runway. The flight instructor stated that during the landing attempt, the engine power did not reduce to idle when the instructor pulled the throttle lever fully aft. The airplane subsequently touched down long on the 5,000-ft runway and traveled off the end and down an embankment, coming to rest upright.

Postaccident examination of the engine did not reveal any anomalies with the throttle linkage. However, the No. 3 cylinder exhaust valve was stuck in the open position. Metallurgical examination of the No. 3 cylinder revealed rough residues and patches in the valve guide, as well as valve guide material that had adhered to the exhaust valve stem. Caked residues were observed around the exhaust valve tip. Measurements of the exhaust valve guide bore’s inside diameter were all below specification for a new valve guide, and the diametral valve-to-guide clearances were also below specification at the middle and inboard end of the guide.

The cylinder had been operated for about 1,072 hours since it was installed new about 3 years before the accident. Available evidence indicates that, over time, the improperly manufactured exhaust valve guide bore allowed a build-up of residual material that led to the exhaust valve becoming stuck in the open position and a partial loss of engine power.

Text from the NTSB. Open the NTSB docket for ERA24LA392 for the full record.