RADAR CTLR DESCRIBED READBACK HEARBACK ERROR INVOLVING SIMILAR ACFT NUMBERS; THAT INCLUDED SEVERAL CTLRS AND SECTORS; REPEATEDLY MISSED BY EVERYONE.

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OUR FACILITY WAS INVOLVED IN A TRULY UNBELIEVABLE HEARBACK/READBACK INCIDENT. ACFT X WAS NEBOUND AT FL390 OVER SOUTHERN INDIANA. HIS DEST WAS ZZZ. ACFT Y WAS EBOUND AT FL410 LNDG YYY. BOTH ACFT WERE IN THE SUPER HIGH SECTOR. THE SECTOR WAS QUITE BUSY; THUS THE SIMILAR CALL SIGNS WENT UNNOTICED BY BOTH THE RADAR CTLR AND THE ASSOCIATE CTLR (D-SIDE); MEANING THE PLTS WERE THUS NOT WARNED. ACFT Y WAS THE FIRST ACFT SWITCHED TO SECTOR 92. THE ACFT Y PLT TOOK THE FREQ CHANGE AND THIS WENT UNNOTICED BY BOTH CTLRS AND BOTH SETS OF FLT CREWS. THE ACFT X THEN CHKS ON FREQ WITH THE R92 CTLR. THEY INITIALLY THOUGHT SOMETHING WAS NOT QUITE RIGHT; AS THE CTLR STARTED TO CALL THE FLT ACFT X; BUT THEN AFTER LOOKING AT THE ACFT Y DATA BLOCK CORRECTED THEMSELVES AND CALLED THE FLT ACFT Y. BEING CALLED ACFT Y AGAIN WENT UNNOTICED BY THE ACFT X FLT CREW. IT SHOULD BE NOTED THAT THE ACFT ALSO CHKED ON LEVEL AT FL390; WHEREAS THE DATA BLOCK SHOWED FL410. THIS AGAIN SHOULD HAVE CAUGHT THE ATTN OF THE R92 CTLR (A SEASONED VETERAN) BUT IT DID NOT. LATER; THIS ACFT Y FLT WAS HANDED OFF AND SWITCHED TO THE NEXT IN-HOUSE SECTOR; R70; AND AGAIN CALLED ACFT Y. ACFT X AGAIN ANSWERED AND AWAY HE WENT. ACFT X THEN CHKED ON THE R70 LEVEL AT FL390. AGAIN THE CTLR DID NOT CATCH THE CALL SIGN OR THE ALT. TO RECAP; THE ACFT Y DATA BLOCK AT FL410 HAS NOW BEEN HANDED OFF TWICE AND BOTH TIMES THE FLT CREW OF ACFT X ANSWERED. BOTH TIMES THIS ACFT X FLT CREW CHKED ON AT FL390 AND BOTH TIMES THE RECEIVING CTLR ACKNOWLEDGED THE CHK-ON BY CALLING THE FLT ACFT Y. AGAIN THE ACFT X CREW DID NOT CATCH THIS EITHER. TO CALL THIS ENTIRE MIX-UP SIMPLY A HEARBACK/READBACK INCIDENT IS AN UNDERSTATEMENT. IT IS UTTERLY ASTOUNDING THAT ALL THE CTLRS INVOLVED AND BOTH SETS OF FLT CREWS REPEATEDLY ANSWERED FOR THE OTHER FLT.