ENG COWL STRUCK ROTOR; RPTR DID AN EMER OFF ARPT LNDG.

Narrative

I RETURNED TO MY CAR WITH THE INTENTION OF RETURNING TO MY OFFICE FOR A HEADSET WHEN I REMEMBERED THAT MY FLT HELMET WAS IN THE TRUNK. I RETURNED TO THE ACFT WITH MY FLT HELMET AND; ONCE AGAIN AS IS MY NORMAL CUSTOM BEFORE FLYING A HELI; I WALKED COMPLETELY AROUND THE MACHINE; SPECIFICALLY CHKING FOR LOOSE PANELS; DOORS; AND SEATBELTS. I STARTED THE ACFT AND LIFTED FROM THE DOLLY. I HAD TO HOVER NEXT TO THE DOLLY FOR ABOUT 1 MIN TO ESTABLISH CONTACT WITH THE TWR. I THEN DEPARTED TOWARD THE SE INTO THE WIND; ACCELERATED TO 60 MPH; AND CLBED AT THAT AIRSPD. I BEGAN MY TURN TO A NW HDG APPROX OVER THE JET HANGARS; AND LEVELED OFF AT ABOUT 300 FT. IT WAS MY INTENTION TO FLY A CIRCLE OF APPROX 1 MI DIAMETER BACK TO THE FBO RAMP. AS I LEVELED OFF AND THE ACFT ACCELERATED; EVERYTHING WAS NORMAL UNTIL THE AIRSPD REACHED ABOUT 120 MPH; AT WHICH TIME I HEARD 2 THUMPS AND FELT THE HELI SHAKE. I IMMEDIATELY LOWERED THE COLLECTIVE; REDUCED MY SPD AND NOTED A LARGE FIELD ABOUT 1/2 A MI AHEAD. I RPTED TO THE TWR THAT I WAS GOING TO MAKE A PRECAUTIONARY LNDG; THE CTLR TOLD ME TO RPT WHEN LNDG WAS ASSURED. THE HELI FLEW PERFECTLY NORMALLY DURING THE APCH; I LANDED AND SHUT DOWN UNEVENTFULLY; AND NOTED THAT THE L ENG ACCESS DOOR HAD COME OPEN INFLT AND STRUCK THE MAIN ROTOR BLADES. I RPTED THE PROB TO X VIA TELEPHONE; HE DROVE ME BACK TO THE ARPT WHERE I CONTACTED THE FLL FSDO OF THE FAA.I SPOKE WITH Y AT XA55 AND TOLD HIM WHAT HAD HAPPENED; AND THAT I WAS NOT SURE WHAT HAD CAUSED THE INCIDENT; BUT THAT FBO HAD ANOTHER HELI IDENTICAL TO THE INCIDENT MACHINE AND WOULD REPLACE THE DAMAGED BLADES AND ENG COVERS WITH PARTS FROM THIS ACFT. Y SAID THAT HE HAD NO PROB WITH THIS; BUT TOLD ME TO BE SURE THAT THE WORK WAS PROPERLY ACCOMPLISHED IN ACCORDANCE WITH MAINT PROCS AND CHKED BY A MECH. HE TOLD ME HE FELT THAT THE CAUSE WAS VERY LIKELY A LATCH FAILURE; AND ASKED THAT AN FAA MALFUNCTION AND DEFECT RPT BE FILED. THE BLADES AND ENG COWLING WERE CHANGED; AND THE ACFT RETURNED TO FBO WITHOUT FURTHER INCIDENT.