THE PLT RPRTD THAT WHEN HE TOOK OFF FM A NRBY NURSE TRUCK, THE WIND WAS FM THE NE AT 5 TO 7 MPH. HE MADE AN OBSERVATION PASS ACROSS THE AREA TO BE TREATED, THEN BGN A DSCNDG RGT TURN TO MAKE A SWATH RUN IN THE OPPOSITE DRCTN. HE STATED HE WAS UNAWARE OF A WIND-SHIFT TO THE NW. SUBSEQUENTLY, THE HELICOPTER ENCOUNTERED WHAT THE PLT THOUGHT WAS WAKE TURBC FM THE OBSERVATION PASS. THE ACFT BGN TO SETTLE & THE PLT INCREASED THE COLLECTIVE IN AN EFFORT TO STOP THE DSCNT. THE PLT SAID THE 'RECOVERY ENDED IN A DEEP CANYON APPROX 150 TO 200 FT DEEP. EMERGENCY TRIP DOOR SOLENOID TO RELEASE LOAD FAILEDTO WORK. WAS ONLY ABLE TO SUSTAIN HOVER FOR APPROX 2 MIN BEFORE A/C SETTLED ON A 30 TO 40 (DEGREE) EMBANKMENT & SLID DOWN 40 FT TO TREES, TAIL FIRST.' RPRTDLY THE DUMP VLV FAILED TO OPERATE DUE TO CORROSION FM CHEMICALS CARRIED ON THE PREVIOUS FLT.

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

Contributing Factors

TERRAIN CONDITION..DOWNHILL

Contributing Factors

OBJECT..TREE(S)

Contributing Factors

TERRAIN CONDITION..MOUNTAINOUS/HILLY

Contributing Factors

WEATHER CONDITION..DOWNDRAFT

Contributing Factors

SPRAY/DUSTING EQUIPMENT..CORRODED

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