Accident Summary
The accident aircraft nosed over during a ditching in the Florida Everglades following an inflight emergency and an emergency descent. Both private-rated pilots were fatally injured when the airplane flipped over and remained inverted and submerged in approximately 4 feet of water.
Aircraft Examination
Examination of the airframe and flight controls revealed no anomalies. The engine, a Lycoming O-320 series, showed significant internal mechanical damage. The interior of the No. 4 cylinder assembly had sustained mechanical damage. Both the top of the piston and the cylinder head exhibited multiple indentations. A hole was present in the top of the piston. The No. 4 exhaust valve tulip had separated from its stem, and fragments of the tulip were found within the combustion chamber and in the exhaust system. Approximately 50 percent of the tulip was missing. The oil pressure screen contained a small amount of aluminum particles.
Engine Examination
Further examination of the power section revealed corrosion on various steel components, including the crankshaft, camshaft, and accessory gears. The bearing surfaces showed evidence of dirt and particle embedment. The NTSB retained the No. 4 cylinder assembly components, including fragments of the exhaust valve, eight tappets and plungers, and the center main bearing for further examination. However, extensive damage to the valve stem and head surfaces precluded any determination of a fracture mechanism.
Maintenance History
Review of the airplane's maintenance records indicated that the last engine overhaul had been performed 23 years prior to the accident. At the time of the accident, the engine had accumulated 1,246.49 hours in service. Lycoming Service Instruction No. 1009AQ specifies that the O-320 series engine should be overhauled after 2,000 hours of service or, for engines not accruing that time, by the twelfth year. Additionally, in 1983 Lycoming changed the part number for the exhaust valve in this engine type. Lycoming Service Bulletin 240 recommends replacing old martensitic stainless steel exhaust valves with new nickel-base superalloy valves at overhaul. Records indicated that this replacement had not been performed. Lycoming Mandatory Service Bulletin No. 388B addresses procedures to determine valve and guide condition; a maintenance record showed that on July 2, 1999, the engine had received a Lycoming 400-hour valve inspection.