NTSB Identification: MIA02FA131.
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Accident occurred Friday, July 12, 2002 in Boca Raton, FL
Probable Cause Approval Date: 03/30/2005
Aircraft: American General Aircraft AA-5, registration: N6024L
Injuries: 2 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The accident airplane nosed over while ditching in the Florida Everglades following an inflight emergency, and an emergency descent. Both private-rated pilots were fatally injured during the ditching when the airplane flipped over,and remained inverted and submerged in about 4 feet of water. Examination of the airframe and flight controls did not reveal any anomalies. Examination of the engine revealed that the interior of the #4 cylinder assembly had incurred mechanical damage, and both the top of the piston and the cylinder head exhibited multiple indentations. In addition, a hole was found to be present in the top of the piston. The No. 4 exhaust valve tulip was found to have separated from the stem, and the oil pressure screen was found to contain a small amount of aluminum particles. During disassembly, fragments of the exhaust valve tulip were found within the combustion chamber and in the exhaust system, and the fragments varied in size and shape, with about 50 percent of the tulip being missing. In addition, the examination revealed that various steel components within the power section exhibited corrosion. Corrosion was found on the crankshaft, camshaft, and accessory gears. The bearing surfaces within the power section exhibited evidence of dirt/particle embedment. The NTSB retained the parts pertaining to the #4 cylinder assembly, to include fragments of the No. 4 exhaust valve, 8 tappets, and plungers, and the center main bearing, for further examination, but extensive damage to the valve stem and head surfaces precluded any determination of a fracture mechanism. Research into airplane's maintenance history revealed that the last engine overhaul had been performed 23 years prior to the accident. At the time of the accident, the engine had accumulated 1246.49 hours in service. Lycoming Service Instruction No. 1009AQ indicates that the O-320 Series engine should be overhauled after 2000 hours time in service. Engines that do not accumulate the hourly time between overhauls, are recommended to be overhauled in the twelfth year. In addition, in 1983 Lycoming changed the part number for the exhaust valve for the accident engine, and Lycoming's Service Bulletin 240 suggests that the old exhaust valves, made from martensitic stainless steel, should be replaced with the new part, made from a nickel-base superalloy, at the time of overhaul, which records indicate had not been performed. "Lycoming Mandatory Service Bulletin No. 388B" addresses the subject: Procedure to Determine Valve and Guide Condition, and a review of maintenance records for subject engine showed that on July 2, 1999, the engine had been given a "Lycoming 400-hour valve inspection."
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The owner/operator's failure to perform an overhaul or comply with a service bulletin 240 which would have probably precluded the continued installation of the number four cylinder exhaust valve and its subsequent failure. Full narrative available
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