DURING TAKEOFF, THE HELICOPTER LIFTED OFF IN AN 80% POWER CHECK & THE PLT BEGAN A NORTHERLY DEPARTURE. BEFORE ACHIEVING TRANSLATIONAL LIFT, THE ROTOR RPM DROPPED TO APRX 85%. THE TORQUE METER INDICATED A SPLIT WITH THE #1 ENG INDICATING ABOUT 55% & THE #2 ENG INDICATING AS LOW AS 39%. THE LOW ROTOR RPM AUDIO & WARNING LIGHT ACTIVATED & THE HELICOPTER BEGAN TO SINK. THE PLT HAD INSUFFICIENT ALT TO RECOVER RPM. HE LANDED THE HELICOPTER IN A CLEAR AREA IN A NOSE HIGH ATTITUDE & WITH FORWARD SPEED. DURING THE LANDING, THE SKIDS WERE DAMAGED (SPREAD), THE HELICOPTER ROCKED FORWARD, THE RADOME WAS DAMAGED & THE TAIL BOOM WAS SEVERED. AN INVESTIGATION REVEALED THAT THE #2 ENG, MAIN FUEL CONTROL, PN3244736-8 HAD AN AIR LEAK AT THE P3-TP-PG REGULATOR AIR DIAPHRAM WJERE A RETAINING SCREW WAS LOOSE. THE SCREW HAD BEEN SAFETY WIRED & SEALED BY THE MANUFACTURER BUT WOULD TURN SLIGHTLY WITHIN THE LIMITS OF THE WIRE. WHEN TIGHTENED, WITHIN THE LIMITS, THE AIR LEAK STOPPED.