A COMMUTER SW3 CAPT EXPERIENCED SELECTIVE HEARBACK AND TOOK OFF FROM THE WRONG RWY.

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FLT X8; DEPARTING FROM SJU. I HAD CONTACTED THE CTL TWR; SAYING 'FLT X8 IS READY FOR TKOF RWY 10;' AND WAS DIRECTED TO HOLD SHORT. I RESPONDED APPROPRIATELY AND CONTINUED TO HOLD SHORT OF RWY 10 AT TXWYS A AND HZ. AFTER AN ACFT LANDED AND THE CTLR DID NOT CONTACT ME; I AGAIN CALLED; 'FLT X8 IS READY FOR TKOF RWY 10.' THE CTLR INSTRUCTED ME TO 'HOLD SHORT FOR LNDG TFC.' HE THEN IMMEDIATELY REKEYED THE MIKE AND SAID 'FLT X8; CONTINUE TO TXWY HZ; CLRED FOR TKOF RWY 8.' UNFORTUNATELY; SINCE I WAS HOLDING SHORT OF RWY 10; I DID NOT EXPECT OR HEAR HIM SAY 'RWY 8' (WHICH IS LOCATED ON THE OTHER SIDE OF THE ARPT). SO; I RESPONDED 'CLRED FOR TKOF; X8.' THE CTLR HEARD THE '8' OF MY CALL SIGN AND ASSUMED I ACKNOWLEDGED RWY 8. THE CTLR CONTINUED WITH OTHER TFC AND WHEN HE REALIZED THE MISUNDERSTANDING; MY COPLT WAS EXECUTING A SET TKOF PROC. (DURING THIS PROC WE WERE EXCHANGING THE APPROPRIATE COMMAND RESPONSES WHICH PRECLUDED US FROM HEARING THE CTLR'S INSTRUCTION TO ABORT AND TAXI CLR.) THE CTLR HAD TO THEN INSTRUCT ANOTHER ACFT THAT WAS ALREADY ON A GAR PROC TO TURN XWIND EARLIER THAN NORMAL. ON CLBOUT I WAS INSTRUCTED TO CONTACT THE CTL TWR VIA TELEPHONE FROM MY DEST. I SPOKE TO THE SUPVR WHO WAS ON DUTY AT THE TIME OF MY DEP FROM SJU. WE DISCUSSED THE SIT AND THE FACT THAT COMS WERE UNCLR. A CONTRIBUTING FACTOR IS THAT THE NEWLY OPEN TXWYS HZ AND HA; WHICH LINK RWY 8 AND RWY 10 HAD NOT BEEN FAMILIAR TO MYSELF. TKOF CLRNC FOR THE OPPOSITE RWY; VIA THESE TXWYS; IS RARELY DONE. FINALLY; I HAVE LEARNED TO ALWAYS MAKE COMPLETE READBACKS OF ALL MY CLRNCS. THE SUPVR SAID SHE WOULD MEET WITH ALL HER CTLRS AND INSTRUCT THEM TO GIVE SEPARATE TAXI AND TKOF CLRNCS IN SITS SUCH AS THIS. BOTH ARE REASONABLE CORRECTIVE ACTIONS THAT WILL ENHANCE COMS AND SAFETY WHEN DEPARTING FROM SJU.