NTSB Identification: LAX93LA263.
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Accident occurred Sunday, June 20, 1993 in LONE PINE, CA
Probable Cause Approval Date: 09/13/1994
Aircraft: SILL/THOMAS LONG EZ, registration: N977ST
Injuries: 1 Minor.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
THE PILOT STATED THAT HE WAS IN LEVEL CRUISE AT 10,500 FEET MSL WHEN THE ENGINE SUDDENLY QUIT. HE MADE A FORCED LANDING ON OWENS DRY LAKE, WHICH WAS SOFT FROM RECENT RAINS. THE NOSE GEAR COLLAPSED AND THE AIRPLANE NOSED OVER INVERTED. POST CRASH EXAMINATION OF THE ENGINE REVEALED THAT THE EXHAUST VALVE HAD FAILED IN THE NUMBER FOUR CYLINDER. THE VALVE HEAD HAD SEPARATED FROM THE VALVE STEM. EXAMINATION OF THE VALVE SPRING AREA REVEALED OVERHEAT SIGNATURES IN THE FORM OF OIL COKING AND OXIDIZATION, AND CARBON DEPOSITS. THE NTSB METALLURGY LABORATORY FOUND THAT THE VALVE STEM WAS DEVOID OF CHROME PLATING IN THE AREA OF THE FRACTURE, WAS REDUCED IN DIAMETER, AND HAD A SIGNIFICANTLY DECREASED MATERIAL HARDNESS, ALL PRINCIPALLY DUE TO HEAT EXPOSURE. POST ACCIDENT EXAMINATION OF THE LOG BOOKS AND THE FAA OPERATING LIMITATIONS REVEALED NO RECORD OF A REQUIRED CONDITION (ANNUAL EQUIVALENT) INSPECTION SINCE THE AIRCRAFT WAS PLACED INTO SERVICE. EXAMINATION OF THE ENGINE REVEALED MANY AREAS OF SUBSTANDARD MAINTENANCE PRACTICES.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the failure of the number four cylinder exhaust valve due to excessive heat exposure and lack of maintenance. Full narrative available
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