PDK LCL CTLR EXPRESSED CONCERN REGARDING FACILITY POLICY THAT REQUIRES GND CTL TO INSTRUCT ACFT TO MONITOR LCL CTL RATHER THAN CALLING THEM.

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PROC AT PDK IS TO HAVE GND CTL INSTRUCT ACFT TO 'MONITOR' LCL CTL. LCL CTL THEN BROADCASTS 'IN THE BLIND' CTL INSTRUCTIONS. I HAVE HAD 2 INCIDENTS WHERE THERE WERE SIMILAR SOUNDING CALL SIGNS ON FREQ BUT I DID NOT KNOW THIS BECAUSE BOTH HAD NOT CONTACTED ME. ONE INCIDENT (ACFT X AND ACFT Y) OCCURRED WHEN I CLRED ACFT X (TALKING TO ACFT Y AT RWY 2R; WHO I HAD ALREADY TALKED TO AND; THEREFORE; COULD USE LAST 3 OF CALL SIGNS) FOR TKOF; NOT KNOWING THAT THE ACFT THAT GND CTL HAD TAKEN TO RWY 2L AT INTXN F WAS ACFT X. SIT WAS CAUGHT BY MYSELF AS ACFT AT RWY 2L STARTED TO ROLL. SIMILAR SIT AT RWY 20L AND RWY 2L AT INTXN G. I CLRED ACFT AT RWY 20L AT INTXN G FOR TKOF USING FULL CALL SIGN. HE GOT ON RWY BUT WAS NOT MOVING VERY FAST AND TFC WAS ON FINAL. I CLRED HIM AGAIN FOR IMMEDIATE TKOF TFC ON FINAL USING LAST 3 OF CALL SIGN. THE ACFT AT RWY 20L FULL LENGTH HAD SAME LAST 3 OF CALL SIGN AND STARTED TO ROLL! I DID NOT KNOW HE HAD SIMILAR SOUNDING CALL SIGN BECAUSE GND CTL HAD INSTRUCTED HIM TO MONITOR ONLY AND HE HAD NOT CALLED ME. POTENTIALLY VERY TRAGIC INCIDENT; I CAUGHT IN TIME; LUCKILY.