THE HELICOPTER TOOK OFF ON A SIGHT-SEEING, PASSENGER FLT IN THE MOUNT ST HELENS AREA. WHEN THE FLT BECAME OVERDUE, A SEARCH WAS INITIATED. LATER, THE HELICOPTER WAS FOUND WHERE IT CRASHED & BURNED IN A HEAVILY WOODED AREA ON RELATIVELY LEVEL TERRAIN, NEAR THE NORTH FORK OF THE TOUTLE RIVER, AT AN ELEVATION OF APRX 800 FT. THERE WERE NO KNOWN WITNESSES. AN EXAM OF THE CRASH SITE REVEALED THAT ONLY THE TREES WITHIN 34 FT OF THE WRECKAGE WERE DAMAGED. THERE WAS EXTENSIVE FIRE DAMAGE TO THE INSTRUMENT PANEL, BUT THE N1 RPM GAGE WAS FOUND AT 72%, THE N2 RPM GAGE WAS AT 43% & THE ROTOR RPM GAGE WAS AT 35%. A LACK OF ROTATIONAL DAMAGE WAS NOTED ON THE MAIN & TAIL ROTOR BLADES. THE FUEL CONTROL, FUEL GOVERNOR & FUEL PUMP WERE DESTROYED BY FIRE. SOME ROTATIONAL DAMAGE WAS NOTED IN THE ENG. HOWEVER, NO PREIMPACT, MECHANICAL FAILURE OR MALFUNCTION WAS VERIFIED.