DHC8 FLC EXIT RWY AS QUESTIONS ARISE CAUSED BY SIMILAR CALL SIGNS WHEN PHL ATTEMPTS TO DEPART ACFT DURING MULTIPLE LNDGS TO INTERSECTING RWYS.

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AT PHL WAITING FOR TKOF. ACFT Y WAS AT FULL LENGTH OF RWY 35. ACFT X (OUR ACFT) WAS AT RWY 35; INTXN K. A JET ACFT (TYPE UNKNOWN) WAS LNDG ON RWY 27R BTWN THE 2 ACFT. ANOTHER ACFT WAS LNDG ON RWY 35 BEHIND THE ACFT LNDG ON RWY 27R. I HEARD PHL TWR SAY 'ACFT X; CAN YOU TAKE AN IMMEDIATE TKOF?' (THE FO SAYS HE DID NOT HEAR THAT CALL.) I TOLD THE FO TO TELL THE TWR WE COULD TAKE THE IMMEDIATE TKOF. THE FO REPLIED THAT WE COULD TAKE IT. I THINK THE RADIO XMISSION WAS BLOCKED BY ACFT Y BECAUSE THE CTLR THEN SAID 'ACFT X; CAN YOU OR CAN YOU NOT TAKE THE IMMEDIATE?' WE ONCE AGAIN SAID WE COULD. THE TWR THEN SAID 'AFFIRMATIVE; THAT IS WHAT I NEEDED TO HEAR. ACFT X CLRED FOR AN IMMEDIATE TKOF.' AS WE TAXIED ONTO THE RWY 35; I THOUGHT 'I HATE TO TURN ON MY LNDG LIGHTS AND BLIND THE PLTS LNDG ON RWY 27R;' SINCE THEY WERE NOW ON ABOUT A 1/4 MI FINAL. AS WE WERE ABOUT READY TO APPLY TKOF PWR; THE CTLR SAID 'ACFT X; ARE YOU CLRED FOR TKOF?' I KNEW THAT THIS WAS NOT OUR CALL SIGN. I ALSO REALIZED THAT THINGS COULD GET BAD IF ACFT Y TRIED TO TAKE OFF BEHIND US WITH THE ACFT ON ABOUT A 1 MI FINAL FOR RWY 35. I DECIDED TO TAXI BACK CLR OF RWY 35 TO BE OUT OF THE WAY TILL THINGS GOT CLRED UP. ACFT Y SAID SOMETHING -- I DON'T KNOW WHAT. PHL TWR THEN SAID 'AM I TALKING TO ACFT X OR ACFT Y?' ACFT Y SAID 'HE TOOK OUR CALL.' PHL TWR THEN SAID 'ACFT Y CLRED FOR IMMEDIATE TKOF.' SINCE I HAD ALREADY COMMITTED TO TAXIING CLR; I CALLED BACK 'ACFT X IS TAXIING CLR OF THE ACTIVE RWY 35.' PHL TWR SAID 'CONFIRM ACFT X IS CLR OF RWY 35.' I RESPONDED 'AFFIRMATIVE; ACFT X IS CLR OF RWY 35.' BY THIS TIME WE WERE OVER THE HOLD LINE. THE ACFT LNDG RWY 35 ASKED IF THEY WERE CLRED TO LAND. PHL TWR RECLRED THEM TO LAND. THEY LANDED. ACFT Y WAS CLRED FOR TKOF. THEN WE (ACFT X) WERE CLRED FOR TKOF. I THINK ACFT Y TOOK OUR IMMEDIATE TKOF CALL CAUSING TWR TO NOT HEAR OUR READBACKS. AT FIRST; IT MADE NO SENSE TO CLR ACFT X FOR AN IMMEDIATE TKOF BECAUSE OF THE ACFT LNDG ON RWY 27R. TWR THEN MIXED UP OUR CALL SIGNS CAUSING MORE CONFUSION. AS WE DEPARTED; TWR SAID TO US WE SHOULD TELL OUR COMPANY ABOUT THESE 2 CALL SIGNS BEING CONFUSING.