What was found
WHILE TRANSITIONING FROM CRUISE INTO HIGH RECON & STARTING A DESCENT FOR A HOSPITAL HELIPAD, LOW ROTOR SYSTEM ACTIVATED. AS IS MY PRACTICE, ALREADY HOLDING THE INCR/DCR SWITCH TO RAISE ROTOR SPEED IF SOMETHING LIKE THIS SHOULD HAPPEN HOWEVER THERE WAS NO RISE IN NR WHEN I LOOKED DOWN AT THE VARTOMS PANEL, NOTICED SYSTEM WAS STILL IN AUTO AND HAD NOT REVERTED TO MANUAL. I DID NO NOTICE HOW LOW THE NR GOT BUT IT WAS DEFIANTLY BELOW THE RED LINE. I SWITCHED THE SYSTEM TO MANUAL AND BROUGHT THE NR BACK UP TO APPROXIMATELY 103%. AT THAT TIME I ABORTED THE LANDING AND ELECTED TO RETURN TO OUR BASE. WHEN BACK IN CRUISE FLIGHT AT 2000' AND 65KIAS I PLACED THE SYSTEM BACK INTO AUTO AND IT RESPONDED APPROPRIATELY.