A BELL 407 DURING AN AUTOROTATION RPM CHK THE RPM DID RECOVER BUT THE ROTOR DECREASED EXCESSIVELY WITH HIGH BLADE ANGLE. ON TOUCHDOWN 2 OF THE 4 ROTORS STRUCK THE TIP OF THE L VERT WINGLET.

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DURING AUTOROTATION RPM CHK; ROTOR RPM DECREASE TO BOTTOM OF GREEN RANGE 95%. I CONTINUED DSCNT TO SEE IF RPM WOULD RECOVER DURING DECELERATION. RPM DID RECOVER TO NORMAL RANGE; AND DURING TERMINATION TO THE GND WITHOUT PWR APPLIED; ROTOR DECREASED EXCESSIVELY LOW WITH VERY HIGH BLADE ANGLE APPLIED. THE BOTTOM SIDE OF 2 OF THE 4 MAIN ROTOR BLADES CONTACTED THE TIP OF THE L SIDE VERT WINGLET. NO OTHER DAMAGE TO THE ACFT OCCURRED. NO SUDDEN STOPPAGE INSPECTION REQUIRED. NO INJURIES TO THE CREW WERE INCURRED AND NO PAX WERE ONBOARD. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT WAS IN AN AUTOROTATION RPM TEST AND THE DSCNT WAS CONTINUED TO CHECK IF THE RPM WOULD RECOVER DURING DECELERATION. THE RPM DID RECOVER TO THE NORMAL RANGE AND AT TOUCHDOWN THE ROTOR DECREASED EXCESSIVELY LOW WITH A HIGH BLADE ANGLE. THE BOTTOM SURFACE OF TWO ROTOR BLADES CONTACTED THE LEFT VERTICAL WINGLET. THE BLADES WHEN CHECKED LATER WERE FOUND TO HAVE SPONGY FEEL; BLADES WERE REMOVED AND SENT TO A SHOP FOR REPAIR.