On October 21, 1989, a Lake LA-4 (registration N1212L) operated by D'alemberte, Talbot S. was involved in an aviation accident near Apalachicola, FL. Investigators recorded the probable cause as: A sticking exhaust valve allowed the piston to contact the valve, and the valve stem cap failed and lodged between the rocker arm and the outer valve spring assembly, causing the #1 exhaust valve pushrod to bend and resulting in engine power loss. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
Shortly after takeoff at about 100 feet AGL, the engine lost power and the pilot made an emergency landing in a swampy area, damaging the aircraft. Investigation found a bent #1 exhaust valve pushrod due to a sticking valve and failed valve stem cap.
Incident Overview
Shortly after takeoff, at an altitude of approximately 100 feet above ground level, the engine lost power. The pilot executed an emergency landing in a swampy area, during which the aircraft sustained damage.
Engine Examination
Post-accident examination of the engine revealed that the #1 exhaust valve pushrod was bent. According to the engine manufacturer, this condition resulted from a sticking exhaust valve, which allowed the piston to contact the valve. Further inspection showed that the valve stem cap had failed and became lodged between the rocker arm and the outer valve spring assembly.
Probable Cause
The engine manufacturer stated that the bent pushrod was caused by a sticking exhaust valve that permitted piston-to-valve contact, compounded by the failure of the valve stem cap which lodged between the rocker arm and outer valve spring assembly. This mechanical failure led to the loss of engine power.