NTSB Identification: LAX92FA064.
The docket is stored on NTSB microfiche number 46448.
14 CFR Part 91: General Aviation
Accident occurred Friday, December 06, 1991 in NUEVO, CA
Probable Cause Approval Date: 04/23/1993
Aircraft: GLASAIR SH-2R, registration: N614LS
Injuries: 1 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 AIRPLANE COLLIDED WITH RUGGED TERRAIN AFTER A LOSS OF ENGINE POWER. IT STRUCK THE NORTH FACE OF 20 DEG SLOPE OF AN EAST-WEST RIDGE, JUST BELOW THE CREST. THE AIRPLANE THEN SLID ABOUT 20 FT DOWN THE SLOPE WHERE A POST-IMPACT FIRE DESTROYED THE PLANE. AN EXAM OF THE ENGINE SPARK PLUGS REVEALED THE #1 & #3 CYLINDER SPARK PLUG GAPS WERE BRIDGED WITH CINDER-LIKE DEPOSITS WITH METALLIC GLOBULES STARTING TO FILL THE FIRING END CAVITY & WORN CENTER ELECTRODES. ACCORDING TO THE SPARK PLUG MANUFACTURER, SEVERELY FOULED PLUGS WILL OPERATE COLDER CAUSING MISFIRES, AND WILL ALSO MISFIRE AT HIGHER POWER BECAUSE OF THE CONDUCTIVE NATURE OF THE DEPOSITS AT ELEVATED TEMPS. BRIDGED GAPS WILL SHORT OUT THE SPARK PLUG. SUCH A MALFUNCTIONED PLUG WILL MISFIRE AT ALL POWER SETTINGS IN A MANNER SIMILAR TO A OIL FOULED PLUG. BRIDGED GAPS BRIDGED BY BEADED LEAD GLOBULE WILL NOT CLEAR UP BY ENGINE OPERATION & CAN BE CORRECTED ONLY BY REPLACING THE MALFUNCTIONING SPARK PLUG WITH A SERVICEABLE UNIT. THE ACDNT TIME WAS ESTD BE AT 1530 PST.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

THE FAILURE OF THE PILOT TO PERFORM PREVENTATIVE MAINTENANCE ON THE AIRPLANE'S POWERPLANT WHICH RESULTED IN A LOSS OF PERFORMANCE DURING AN UNKNOWN PHASE OF OPERATION. CONTRIBUTING TO THE ACCIDENT WAS FOULED SPARK PLUGS AND THE PARTIAL LOSS OF AIRCRAFT PERFORMANCE.

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