Narrative:

It was the first trip to bos for both crew members. We had planned a takeoff on runway 4L. As we taxied out, the runway was changed to runway 9. We were to hold short of runway 4L behind another aircraft, with clearance to runway 9. We were told to switch to tower, which we did. The aircraft ahead was cleared to cross. Earlier, we had been told to follow that aircraft to runway 9. So we began to roll forward, but we were unsure of our clearance. I told the captain I would get a clarification from the tower. The frequency was very congested, and by the time I got through, we were told to hold short of runway 4L. By this time our slow roll forward had allowed the nose of the aircraft across the hold line for runway 4L. We stopped with the nosewheel just short of the line. About 1 min later, an aircraft landed on runway 4L. We were then cleared to cross runway 4L, and subsequently cleared for takeoff on runway 9 for an uneventful flight to sea. Unfamiliarity with the airport was certainly a factor in this incident. Unclr taxi instructions still leave me wondering which of 2 possibilities is correct: 1) we were indeed cleared to cross runway 4L, but because of our slow progress and inability to contact the tower quickly, that clearance was then rescinded due to the proximity of the aircraft on final, or 2) we were to hold short of runway 4L, in which case the earlier instructions to follow the aircraft ahead and taxi to runway 9 led us to improperly believe we were cleared to cross the runway. In conclusion, there was never any danger to the aircraft or passenger. Had tower thought our proximity to runway 4L hazardous, he had ample opportunity to send the landing traffic around. In the future, however, it would be wise for us to leave the brakes set until our runway crossing clearance is certain.

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Original NASA ASRS Text

Title: ACR FLC STARTS TO CROSS BOS RWY DURING TAXI OUT AND THEN AFTER QUESTIONING TWR, WAS TOLD TO HOLD SHORT. 1 MIN LATER, AN ACFT LANDED ON THE RWY.

Narrative: IT WAS THE FIRST TRIP TO BOS FOR BOTH CREW MEMBERS. WE HAD PLANNED A TKOF ON RWY 4L. AS WE TAXIED OUT, THE RWY WAS CHANGED TO RWY 9. WE WERE TO HOLD SHORT OF RWY 4L BEHIND ANOTHER ACFT, WITH CLRNC TO RWY 9. WE WERE TOLD TO SWITCH TO TWR, WHICH WE DID. THE ACFT AHEAD WAS CLRED TO CROSS. EARLIER, WE HAD BEEN TOLD TO FOLLOW THAT ACFT TO RWY 9. SO WE BEGAN TO ROLL FORWARD, BUT WE WERE UNSURE OF OUR CLRNC. I TOLD THE CAPT I WOULD GET A CLARIFICATION FROM THE TWR. THE FREQ WAS VERY CONGESTED, AND BY THE TIME I GOT THROUGH, WE WERE TOLD TO HOLD SHORT OF RWY 4L. BY THIS TIME OUR SLOW ROLL FORWARD HAD ALLOWED THE NOSE OF THE ACFT ACROSS THE HOLD LINE FOR RWY 4L. WE STOPPED WITH THE NOSEWHEEL JUST SHORT OF THE LINE. ABOUT 1 MIN LATER, AN ACFT LANDED ON RWY 4L. WE WERE THEN CLRED TO CROSS RWY 4L, AND SUBSEQUENTLY CLRED FOR TKOF ON RWY 9 FOR AN UNEVENTFUL FLT TO SEA. UNFAMILIARITY WITH THE ARPT WAS CERTAINLY A FACTOR IN THIS INCIDENT. UNCLR TAXI INSTRUCTIONS STILL LEAVE ME WONDERING WHICH OF 2 POSSIBILITIES IS CORRECT: 1) WE WERE INDEED CLRED TO CROSS RWY 4L, BUT BECAUSE OF OUR SLOW PROGRESS AND INABILITY TO CONTACT THE TWR QUICKLY, THAT CLRNC WAS THEN RESCINDED DUE TO THE PROX OF THE ACFT ON FINAL, OR 2) WE WERE TO HOLD SHORT OF RWY 4L, IN WHICH CASE THE EARLIER INSTRUCTIONS TO FOLLOW THE ACFT AHEAD AND TAXI TO RWY 9 LED US TO IMPROPERLY BELIEVE WE WERE CLRED TO CROSS THE RWY. IN CONCLUSION, THERE WAS NEVER ANY DANGER TO THE ACFT OR PAX. HAD TWR THOUGHT OUR PROX TO RWY 4L HAZARDOUS, HE HAD AMPLE OPPORTUNITY TO SEND THE LNDG TFC AROUND. IN THE FUTURE, HOWEVER, IT WOULD BE WISE FOR US TO LEAVE THE BRAKES SET UNTIL OUR RWY XING CLRNC IS CERTAIN.

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.