PIPER PA-32-260 — Los Angeles, CA

What happened

Shortly after takeoff, the pilot reported to air traffic control that the airplane was experiencing engine problems and he was going to make an off-airport landing. The airplane contacted a semi-truck and a concrete barrier during the landing in a shipping harbor.

Postaccident examination of the engine revealed that the No. 6 cylinder exhaust valve head was separated from the stem. A fatigue crack was found in the exhaust valve upper spring seat of the No. 6 cylinder assembly that likely led to the release of the exhaust valve. The crack formed at the base of the cup that housed the valve stem keys, causing a portion of the flange that supported the keys to separate. This could have allowed the exhaust valve to drop into the cylinder, impacting the piston, the cylinder head, and the exposed end of the valve guide before being sheared through the stem near the stem-to-fillet transition.

The findings suggest that the No. 6 exhaust valve may have been floating, which would have removed the compressive load on the keys and allowed them to move and rub against the support flange and sidewall of the spring seat cup. The compression test of the exhaust valve springs indicated that they did not pass, suggesting that a floating valve is a possibility. However, the No. 5 exhaust valve springs also did not pass, and similar wear features around the key cup were not observed in that instance. Because the keys and valve stem were not found (likely destroyed during the continual operation with the failed valve), it could not be determine if there was some issue with either component that could have contributed to the failure.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.