POSSIBLE CALL SIGN MIX-UP BY GND CTLR AT EDDF ARPT MAY HAVE CAUSED AN ACR TO CROSS A RWY WITH TFC ON SHORT FINAL.

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TAXIED ON TXWY A TO TXWY K AT RWY 7L AT FRANKFURT (EDDF). APCHING TXWY K; GND SWITCHED US TO TWR. AT TXWY K TWR SAID 'ACR X ...;' AND I DIDN'T UNDERSTAND THE REST. SO I SAID; 'SAY AGAIN FOR ACR X.' TWR REPLIED; 'ACR X CROSS RWY 7L AND SWITCH TO 121.95.' WE SAW AN ACFT ON SHORT FINAL BUT WE THOUGHT OKAY WE COULD STILL SAFELY CROSS. I'VE SEEN CLOSER CROSSES AT OTHER ARPTS (ATL; DFW; ETC). HE WAS ABOUT 3/4 TO 1 MI OUT. AS WE APCHED THE HOLD SHORT LINE TWR SAID; 'ACR X HURRY ACROSS RWY 7L.' I TURNED TO THE CAPT AND SAID; 'YOU BETTER START BEATING THE HORSES;' BECAUSE HE WAS A LITTLE SLOW ON THE PWR. HE REPLIED; 'YEAH OKAY WE CAN MAKE IT.' AS OUR NOSE ENTERED THE RWY; TWR YELLED;' ACR X HOLD SHORT.' I THOUGHT 'WELL HE CHANGED HIS MIND.' BUT BY NOW WE WERE IN THE RWY AND GOING FAST. SO I SAID; 'IT'S TOO LATE NOW.' I WAS SURPRISED HE HAD CHANGED HIS MIND BUT HE SAID; 'YEAH; OKAY.' AFTER WE CROSSED WE ASKED TWR IF WE SHOULD HOLD SHORT OF RWY 7R; TO WHICH HE REPLIED; 'YES; AT LEAST HOLD SHORT OF THIS RWY.' HE THEN EXPLAINED THAT THE CLRNC TO CROSS HAD BEEN FOR ACR Y XING RWY 7L AT TXWY B AT THE EXTENDED CTRLINE AT THE END OF RWY 7L. IT ALSO TURNS OUT THAT 121.95 IS APRON CTL (WHERE ACR Y WAS GOING). THE CAPT AND I ARE BOTH SURE TWR SAID ACR X BOTH TIMES. HOWEVER; WE WERE RUSHING TO MAKE A SLOT TIME. THIS WAS ALSO DAY 9 OF A 9 DAY TRIP AND WE WERE TIRED. ADDITIONALLY; THE TEMPO OF OPS AT FRANKFURT HAS INCREASED SINCE THE WAR STARTED AND AT TIMES TWR SEEMS A LITTLE OVERWHELMED. I HAVE ALSO HEARD FRA GND AND TWR MIX UP ACR CALL SIGNS BEFORE. THIS DAY WE DID NOT CATCH IT DUE TO OUR LOWERED SITUATIONAL AWARENESS AND FATIGUE. OF COURSE TWR SEEMED JUST AS SURE HE SAID ACR Y AND NEVER CLRED US TO CROSS. AFTER AN INCIDENT LIKE THIS I WOULD NEVER SWEAR THAT I WAS 100% IN THE RIGHT.