THE PLT WAS ON AN EXTERNAL LOAD OPERATION WITH A 100 FT LONG LINE. THE LONG LINE HAD 4 REMOTE HOOKS, OF WHICH, 3 HAD CABLE BAGS ATTACHED. WHILE WAITING FOR THE 4TH BAG TO BE FILLED, HE DECIDED TO LAND IN AN OPEN AREA. HE SET THE EXTERNAL LOAD DOWN & LAID THE LONG LINE OUT OVER THE GROUND, 'LANDING THE HELICOPTER WHEN THE LONG LINE WAS NEARLY EXTENDED AWAY FROM THE LOAD.' WHEN THE 4TH BAG WAS READY TO BE SLUNG OUT, HE LIFTED OFF IN WINDS THAT WERE GUSTING TO 15 KTS. AT A HEIGHT OF ABOUT 40 FT, HE MADE A LEFT, RUDDER TURN (X-WIND) TO BETTER OBSERVE HIS LONG LINE. HE REALIZED THAT HE WAS DRIFTING DOWNWIND AT ABOUT THE TIME HE THOUGHT HE DETECTED A POWER SURGE. HE DIRECTED HIS ATTENTION TO THE ENG INSTRUMENTS. AT ABOUT THE SAME TIME, THE HELICOPTER ROLLED ON ITS LEFT SIDE & CRASHED. AN EXAM OF THE WRECKAGE WAS MADE, BUT NO MECHANCIAL PART FAILURE/MALFUNCTION WAS FOUND.