A300 CAPT REPORTS UNSAFE LANDING GEAR DURING APPROACH. ATTEMPTS TO EXTEND GEAR BY ALTERNATE MEANS ARE UNSUCCESSFUL UNTIL PROBLEM CLEARS UP ON ITS OWN AND GEAR EXTENDS.

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ON FINAL APCH TO ZZZ; LOWERED LNDG GEAR. L MAIN DID NOT INDICATE DOWN AND LOCKED ON THE FRONT PANEL; OVERHEAD PANEL OR MAIN LNDG GEAR DOWN LOCK INDICATORS. RECYCLED GEAR WITH SAME RESULT. NOTIFIED TWR OF PROB AS WE WENT AROUND. REQUESTED VECTORS FOR TROUBLESHOOTING. EMER DECLARED. COMPLIED WITH ALL ECAM AND CHKLIST ITEMS. MANUALLY LOWERED GEAR. NO HELP. PERFORMED SIDESLIPS IN BOTH DIRECTIONS AT INCREASED SPD. NO HELP. FINALLY; THE GEAR INDICATED DOWN AND LOCKED. WE MADE A LOW LEVEL FLY-BY OVER THE RWY FOR GND PERSONNEL TO INSPECT GEAR. ALL GND RPTS WERE NORMAL. WE LANDED AND STOPPED ON THE RWY. OUR COMPANY MAINT TOWED US TO THE RAMP. AS A CREW; I THOUGHT WE WERE VERY LOGICAL AND COORDINATED IN HANDLING THIS EMER. NOTHING WAS A MYSTERY AND ALL OPINIONS WERE VOCALIZED AND EVALUATED. GREAT JOB BY THE FO BACKING ME UP ON ALL CHKLISTS AND SORTING EVERYTHING OUT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: MAINTENANCE COULD NOT FIND A REASON FOR THE GEAR TO FAIL TO EXTEND. THE ACFT WAS FERRIED THE NEXT DAY WITH A DIFFERENT FLT CREW AND THE GEAR EXTENSION PROBLEM OCCURRED AGAIN. THE REPORTER HAS NOT RECEIVED AN EXPLANATION FROM THE COMPANY.