The 6,900-hour commercial helicopter pilot was returning to his home base helipad after a public relations static display mission at a nearby airport. The flight included a planned fuel stop at an intermediate airport on the way back to home base. During the approach, while the helicopter was approximately 100 feet above ground level (AGL), the pilot reported in the Pilot Operator Aircraft Accident Report (NTSB Form 6120.1/2) that available engine power continued to decrease while he maintained a constant pitch setting on the approach. The pilot initiated the immediate action steps of the emergency procedures for a loss of engine power by confirming that the throttle was in the full-open position while lowering the collective to initiate an autorotation. The pilot was forced to increase collective pitch to avoid power lines which resulted in a decay of rotor RPM to 90 percent available for the landing. The aircraft touched down tail low while in a decelerating flare and the tail stinger contacted the ground first. As additional collective pitch was applied to cushion the landing, the pilot leveled the aircraft and landed upright on the intended helipad. The pilot and his two passengers were uninjured and the helicopter sustained structural damage. The engine was removed from the helicopter and shipped to the factory for examination and test run. An FAA inspector from provided on-site assistance to insure the engine was properly crated and shipped to the factory. The engine evaluation and test run was performed on November 9, 2005, under the supervision of an FAA inspector. A written statement provided by the inspector stated that no discrepancies were noted during all phases of the engine run and that the engine produced above rated power at take off power setting. The reason for the reported loss of engine power could not be determined.