AN EMS HELI PLT LOST A HATCH COVER THAT DAMAGED THE TAIL ROTOR AND FIN WHEN IT FLEW OFF INFLT.

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WHILE DISCUSSING THIS INCIDENT WITH MR X; HE SAID THAT HE THOUGHT IT WOULD BE A GOOD IDEA TO REPLACE THIS INSPECTION HATCH WITH A PLEXIGLAS SEE-THROUGH COVER. HE FEELS THAT THESE TYPE OF HATCHES FAIL TOO OFTEN. DURING A MEDICAL FLT TO LOCATION B FROM LOCATION A IN HELI; THE HYD RESERVOIR HATCH SEPARATED FROM THE ACFT STRIKING THE MAIN AND TAIL ROTORS; AND THE VERT FIN. I CONDUCTED A NORMAL PREFLT WHICH INCLUDED CHKING THE HYD FLUID LEVELS. TO CHK THOSE LEVELS; I OPENED THE ACCESS HATCH IN THE R SIDE OF THE CTL'S COWLING ON TOP OF THE CABIN FORWARD OF THE XMISSION AREA. I REMEMBER CLOSING THE HATCH AND ROTATING THE SILVER LATCHING PIN AND GIVING THE PIN A PULL TO ENSURE SECURITY OF THE HATCH. AT APPROX XA30 AM; I RECEIVED A CALL TO FLY TO THE LOCATION B HOSPITAL. I REFUELED THE HELI AND CONDUCTED A QUICK WALKAROUND WHICH INCLUDED A VISUAL CHK OF ALL HATCHES AND COWLINGS. AFTER SHUTDOWN AT LOCATION B; I NOTICED THAT THE HYD ACCESS HATCH WAS MISSING. THINKING THAT IT WAS IN THE AREA OF THE XMISSION; I USED MY FLASHLIGHT TO SEARCH FOR IT VISUALLY. NOT FINDING IT; I PROCEEDED TO DO A WALK AROUND CHKING FLUID LEVELS AND GENERAL CONDITION AND SECURITY. WHEN I GOT TO THE REAR OF THE ACFT; THE TAIL ROTOR WAS IN A NEARLY VERT POS; I USED MY FLASHLIGHT TO SCAN THE SIGHT GAUGES AND THE TAIL ROTOR BLADES THEMSELVES. IT WAS STILL VERY DARK AT THIS TIME. I MISSED SEEING THE DAMAGE BECAUSE THE DAMAGE WAS TO THE TOP TAILROTOR BLADE AND THE GOUGE IN THE VERT FIN WAS MASKED BY THE LOWER TAILROTOR BLADE. THE PATIENT HAD DIED OF A GUNSHOT WOUND TO THE HEAD AND WE WERE TO GO BACK TO LOCATION A EMPTY. ACCESS HATCH; NOT BEING IN THE MEL; DID NOT REQUIRE FURTHER ACTION AT THAT TIME. THE RETURN FLT WAS NORMAL. Y (WHO WAS THE DAY PLT) WAS WAITING FOR ME TO RETURN FROM THE FLT. AFTER SHUTDOWN; WE DISCUSSED THE MISSING HATCH AND OPENED THE R SIDE XMISSION COWL TO SEARCH FOR THE HATCH. NOT FINDING ANYTHING; I WENT INSIDE TO FINISH THE PAPER WORK WHILE Y CONDUCTED HIS PREFLT. IT WAS THEN (DAYLIGHT BY NOW) THAT THE DAMAGE TO THE TAIL ROTOR AND VERT FIN WAS FOUND. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: RPTR STATED THAT HE NOTICED NO PROBLEMS IN FLT CHARACTERISTICS DESPITE DAMAGE TO TAIL ROTOR BLADES AND VERT FINS. MAINT HISTORY WAS INVESTIGATED. THIS SAME HATCH HAD COME OFF 3 TIMES PREVIOUSLY. EVIDENTLY INFLT WEAR ON LOCKING PIN IS COMMON AND THE CURRENT HINGE ALLOWS DOOR TO OPEN 90 DEGS TO ACFT. SOLUTION HAS BEEN TO HINGE DOOR; SO THAT IF ACCIDENTALLY OPENS; IT WILL ALLOW THE DOOR TO TRAIL.