Narrative:

While I was talking with agent on ground during pushback from gate, first officer received taxi clearance. After terminating communication with pushback personnel, I asked first officer what runway we were using. He replied, '4R, hold short of 4L.' approaching 4L ground controller cleared us to cross 4L and switch to tower. Approaching runway 9 I asked first officer if we were cleared to cross. He responded, 'we were told to taxi to 4R, nothing said about holding short of 9.' as we approached 9 tower said, 'taxi in position and hold.' we still had an engine to start, so first officer advised we needed a couple of mins. Tower responded, 'taxi in position and hold, advise when ready.' as we crossed runway 9 and proceeded to 4R, tower responded, 'runway 9 was the runway.' at this point we were about 1000' from runway 4R threshold. Boston had been at CAT ii minimums all day and had just improved within the past hour. Had the visibility been poor enough for the tower to be unable to see us we would have taxied onto 4R, the landing runway. Solution: tower should be required to always state runway when giving instructions, no exceptions. Had the tower said, 'taxi into position runway 9 and hold,' I would have immediately caught my first officer's error in departure runway. Both xmissions by tower did not include runway assignment. Only the tower visually seeing us prevented a tragedy.

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Original NASA ASRS Text

Title: THOUGHT CLEARED INTO POSITION AND HOLD 4R TWR WANTED RWY 9.

Narrative: WHILE I WAS TALKING WITH AGENT ON GND DURING PUSHBACK FROM GATE, F/O RECEIVED TAXI CLRNC. AFTER TERMINATING COM WITH PUSHBACK PERSONNEL, I ASKED F/O WHAT RWY WE WERE USING. HE REPLIED, '4R, HOLD SHORT OF 4L.' APCHING 4L GND CTLR CLRED US TO CROSS 4L AND SWITCH TO TWR. APCHING RWY 9 I ASKED F/O IF WE WERE CLRED TO CROSS. HE RESPONDED, 'WE WERE TOLD TO TAXI TO 4R, NOTHING SAID ABOUT HOLDING SHORT OF 9.' AS WE APCHED 9 TWR SAID, 'TAXI IN POS AND HOLD.' WE STILL HAD AN ENG TO START, SO F/O ADVISED WE NEEDED A COUPLE OF MINS. TWR RESPONDED, 'TAXI IN POS AND HOLD, ADVISE WHEN READY.' AS WE CROSSED RWY 9 AND PROCEEDED TO 4R, TWR RESPONDED, 'RWY 9 WAS THE RWY.' AT THIS POINT WE WERE ABOUT 1000' FROM RWY 4R THRESHOLD. BOSTON HAD BEEN AT CAT II MINIMUMS ALL DAY AND HAD JUST IMPROVED WITHIN THE PAST HR. HAD THE VISIBILITY BEEN POOR ENOUGH FOR THE TWR TO BE UNABLE TO SEE US WE WOULD HAVE TAXIED ONTO 4R, THE LNDG RWY. SOLUTION: TWR SHOULD BE REQUIRED TO ALWAYS STATE RWY WHEN GIVING INSTRUCTIONS, NO EXCEPTIONS. HAD THE TWR SAID, 'TAXI INTO POS RWY 9 AND HOLD,' I WOULD HAVE IMMEDIATELY CAUGHT MY F/O'S ERROR IN DEP RWY. BOTH XMISSIONS BY TWR DID NOT INCLUDE RWY ASSIGNMENT. ONLY THE TWR VISUALLY SEEING US PREVENTED A TRAGEDY.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.