RWY INCURSION.

Narrative

BACK TAXI DOWN RWY 18L WHEN CLRED TO CROSS RWY 18L BY THE CTLR. HE TOLD US WE WERE SUPPOSED TO CROSS IT AND THEN TAXI TO THE END. WE THEN CAME BACK TO THE INTXN WHERE WE WERE CLRED TO CROSS AND EXITED THE RWY. THEN WE USED TXWY TO GO TO THE END AS FIRST INTENDED BY THE CTLR. THE END RESULT WAS THAT NO ONE WAS HURT OVER OUR MISCOM WITH ATC. THE CORRECTIVE ACTION IS TO ASK FOR PROGRESSIVE TAXI INSTRUCTIONS THE NEXT TIME WE ARE IN THIS SIT. SUPPLEMENTAL INFO FROM ACN 318669: WE WERE CLRED TO TAXI TO RWY 18L FOR INTXN DEP. WE ADVISED GND CTL THAT WE NEEDED THE FULL LENGTH (BACK TAXI). GND CTL THEN ISSUED CLRNC TO TAXI TO RWY 18L VIA TXWY D; CROSS RWY 23 AND HOLD SHORT OF RWY 18L AT TXWY M. UPON REACHING TXWY M; GND CTL CLRED US TO CROSS RWY 18L AND THEN TAXI TO RWY 18L. THIS CONFUSED US; SINCE GND CTL DID NOT ISSUE ANY INSTRUCTIONS HOW TO GET TO RWY 18L; AND SINCE WE COULD NOT SEE ANYMORE TXWYS LEADING TO THE APCH END OF RWY 18L; AND HAD PREVIOUSLY REQUESTED A BACK TAXI; WE PROCEEDED TO BACK TAXI DOWN RWY 18L A SHORT DISTANCE TO THE END INSTEAD OF JUST XING RWY 18L. WHEN THE GND CTLR STATED THAT HE WANTED US TO CROSS RWY 18L ONLY; WE QUICKLY VACATED THE RWY.