THE ACFT DEPARTED PAGE AT ABOUT 1150. AT ABOUT 1238 THE ACFT STRUCK THE SOUTH SLOPE OF A 6,280-FT CANYON WALL AT ABOUT 6,000 FT MSL. THE CANYON IS ONE OF A SERIES OF ABOUT FIVE 'FINGER' CANYONS FORMING THE VERMILION CLIFFS GROUP. SIGMENT LIMA 15 IN EFFECT CALLED FOR OCCASIONAL SEVERE TURBULENCE BELOW 16,000 FT ESPECIALLY WITHIN 50 MI OF ROUGH TERRAIN. THE AREA FORECAST CALLED FOR OCCASIONAL MODERATE TRUBULENCE SURFACE TO 15,000 FT DUE TO STRONG WESTERLY WINDS. A PLT WHO LANDED AT PAGE AT 1345 STATED HIS FLT WAS MARKED BY LIGHT TO OCCASIONALLY MODERATE TURBULENCE WITH FREQUENT SUSTAINED UP & DOWN DRAFTS. HE ALSO STATED THAT DURING HIS ARRIVAL THE WINDS WERE 160 DEG AT 28 MPH GUSTING TO 45 MPH. REPORT OF ENGINE TEARDOWN REVEALED THAT NONE OF THE SPARKPLUGS WERE TORQUED, & THE SPARKPLUGS OF CYL #4 WERE ONLY FINGER-TIGHT. IN ADDITION, CYL #1'S EXHAUST VALVE LEAKED, CYL #3'S RINGS LEAKED, & CYL #4'S INTAKE VALVE & RINGS LEAKED.

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

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

Contributing Factors

WEATHER CONDITION..TURBULENCE

Contributing Factors

WEATHER CONDITION..HIGH WIND

Contributing Factors

WEATHER CONDITION..HIGH DENSITY ALTITUDE

Contributing Factors

WEATHER CONDITION..DOWNDRAFT

Contributing Factors

TERRAIN CONDITION..MOUNTAINOUS/HILLY

Contributing Factors

TERRAIN CONDITION..RISING

Contributing Factors

IGNITION SYSTEM,SPARK PLUG..UNDERTORQUED

Contributing Factors

ENGINE ASSEMBLY,VALVE,INTAKE..LEAK

Contributing Factors

ENGINE ASSEMBLY,RING..LEAK

Contributing Factors

AIRCRAFT PERFORMANCE,CLIMB CAPABILITY..DETERIORATED

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