AS THE HELICOPTER WAS CLIMBING OVER RISING TERRAIN AT 300' TO 400' AGL, THE PLT NOTED ALTIMETER & AIRSPEED INDCNS OF 8700' & 60 MPH. AFTER CLIMBING AN ADNL 2 MIN TO APRX 10,000' (12,000' DENSITY ALT), HE NOTICED THE ROTOR RPM WAS BLEEDING OFF. HE MADE A 180 DEG RGT TURN & HEADED DOWN SLOPE, BUT THE HELICOPTER 'CRASH LANDED' AT THE 8500' LEVEL. THE PLT RPRTD THE WINDS WERE FROM THE NW AT 5 KTS & THE TEMP WAS 60 DEG F. APRX 26 MI NW AT KAILUA-KONA, THE 1750 WIND WAS FROM 030 DEG AT 7 KTS. ACCORDING TO WT & BALANCE RECORDS, THE ACFT WAS LOADED TO 3171 LBS (28 LBS UNDER MAX WT LMT).CALCULATIONS SHOWED THE HELICOPTER WOULD HAVE HAD TO CLIMB AT A RATE OF 616'/MIN TO MAINT A 60 MPH CLIMB OVER THE TRRN. ACCORDING TO THE FLT MANUAL, AT 3171 LBS, THE HELICOPTER'S MAX RATE OF CLIMB AT 10,000' WITH 60 DEG AIR TEMP WOULD HAVE BEEN 450'/MIN. ALSO, THE MANUAL SHOWED THE HELICOPTER WAS NOT ABLE TO HOVER OUT OF GROUND EFFECT AT AN ALT & TEMP OF 10,000' & 60 DEG, WHEN THE GROSS WT WAS AT OR ABOVE 2800 LBS. NO PREIMPACT MECH PROBLEMS WERE FND.