DURING INITIAL TKOF ROLL AT BOS; A DEPARTING AIR CARRIER TURBOJET TOOK EVASIVE ACTION BY SWERVING AROUND A COMMUTER TURBOPROP MOVING TOWARD RWY 33L ON TXWY G.

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WE WERE TOLD TO TAXI INTO POS AND HOLD ON RWY 33L AND TO KEEP POWER UP FOR AN IMMEDIATE FOR CLOSE IN TFC. WE WERE CLRED FOR TKOF BEFORE COMPLETING THE TURN TO LINE UP AND STARTED THE ROLL IMMEDIATELY. AT SOME POINT AFTER SET TKOF THRUST CALL; I NOTICED A SAAB 340 APCHING THE RWY AT TXWY G. THE SAAB WAS MOVING VERY SLOWLY SO I ASSUMED HE WOULD HOLD SHORT. I POINTED OUT THAT THE SAAB WAS GETTING CLOSE TO THE RWY BY SAYING 'WHAT IS THIS GUY DOING?' WE WERE ALREADY ABOVE 80 KTS IN THE HIGH SPD REGIME SO WE FELT ABORTING WAS INAPPROPRIATE DUE TO THE FACT THAT THE SAAB WAS MOVING SO SLOWLY WE THOUGHT HE INTENDED TO STOP. BY THE TIME WE REALIZED HE WAS NOT STOPPING; WE WERE ABOVE 100 KTS AND ABORTING WAS OUT OF THE QUESTION. TWR SAID 'ACR Y STOP' OVER THE FREQ WITH NO CALL SIGN. THE SAAB STOPPED IMMEDIATELY AND MADE A SLIGHT TURN AWAY FROM THE RWY; LEAVING IS RIGHT WING OVER THE RWY; WE THINK. I BROUGHT THE ACFT SLIGHTLY RIGHT OF CTRLINE TO PROVIDE SOME MARGIN FOR ERROR AND CONTINUED THE TKOF WITHOUT INCIDENT. WE HEARD ATC GIVE GAR INSTRUCTIONS TO ANOTHER ACFT AND BELIEVE IT WAS THE ONE LNDG BEHIND US. SUPPLEMENTAL INFO FROM ACN 503081: DURING TKOF ON RWY 33L AT BOS I BECAME AWARE OF AN ACR Y SAAB 340 SLOWLY MOVING ON TXWY GOLF TOWARD RWY 33L. ALTHOUGH INITIALLY I HAD NO REASON TO BELIEVE THE SAAB WOULDN'T STOP PRIOR TO RWY 33L; AT APPROX 90 KNOTS IT BECAME APPARENT THE SAAB WAS PAST THE HOLD LINE AND ALMOST ONTO THE RWY. AT THIS POINT ATC ORDERED THE SAAB TO STOP; WHICH HE DID IMMEDIATELY. I DECIDED NOT TO ABORT THE TKOF; FEELING THAT I HAD THE SAAB BEAT THROUGH THE RWY 33L TXWY GOLF INTXN AND THAT DOING SO MAY HAVE CAUSED A COLLISION HAD THE SAAB NOT STOPPED. WE PASSED GOLF INTXN AT 110 KIAS. V1 WAS 149 KNOTS. SUPPLEMENTAL INFO FROM ACN 501972: I WAS CAPT OF ACR Y FROM BOS TO ROC. WE HAD COMPLETED THE STARTING CHKS AND WERE READY TO TAXI AND RECEIVED INTRUCTIONS TO TAXI TO RWY 27 FROM OUR RAMP AREA VIA TXWYS KILO; CHARLIE AND DELTA WITH INSTRUCTIONS TO HOLD SHORT OF RWY 33L AT DELTA. AS WE TAXIED; WE WERE GIVEN THE OPTION OF DEPARTING FROM RWY 33L AT INTXN GOLF. WE HAVE PERFORMANCE DATA FOR THAT LOCATION SO I ELECTED TO ACCEPT THEIR OFFER. NEW INSTRUCTIONS WERE TO HOLD SHORT OF RWY 33L AT INTXN GOLF. AS WE WAITED THERE WE HEARD WHAT WE THOUGHT WERE INTRUCTIONS FOR ACR Y; 'TAXI POS AND HOLD;' SO I CALLED FOR THE BEFORE TKOF CHKS AND THE FO RESPONDED TO ATC 'ACR Y; POS AND HOLD.' WE PROCEEDED PAST THE HOLD LINE TOWARD THE RWY; AT THAT POINT I ASKED THE FO IF WE HAD BEEN CLRED FOR TKOF TO MAKE SURE I HAD NOT MISSED A XMISSION; AND HE REPLIED; 'NO; POS AND HOLD.' WE WERE PAST THE HOLD SHORT BARS ABOUT 30 FT FROM THE EDGE OF THE RWY WHEN WE HEAR 'ACR Y; STOP.' WE STOPPED AND SAW THAT ACR X HAD BEGUN A TKOF ROLL ON RWY 33. WE WERE TOLD TO MAKE A U TURN AND EXIT AND HOLD SHORT AT GOLF WHICH WE DID AND THEN WE WERE GIVEN A TKOF CLRNC. VFR CONDITIONS PREVAILED; AND CREW IS FAMILIAR WITH OPS AT LOGAN ARPT AND OTHER HIGH DENSITY AREAS. CONVERSATION WITH CTLR REVEALED THAT AFTER ACR X WAS CLRED FOR TKOF THERE IS ONLY A GARBLED XMISSION. ALSO; ONE FREQ WAS IN USE FOR RWY 33L AND RWY 27; 128.8. USUALLY 128.8 IS FOR 33L AND 119.1 IS USED FOR RWY 27; HOWEVER; ONLY ONE WAS IN USE AT THE TIME. IT WAS A BUSY TIME OF THE DAY; AND THEY WERE DOWN TO USING ONLY 2 RWYS FOR OPS DUE TO WINDS; HOWEVER; WINDS WERE NOT EXCEEDING 20 KNOTS. CREW WAS WELL RESTED. FLT WAS BEHIND SCHEDULE; HOWEVER THERE WAS NO RUSH AS SUCH. CAN ONLY SURMISE THAT THE CTLR ERRONEOUSLY USED OUR CALL SIGN OR THAT WE MISTOOK SOMEONE'S CALL SIGN FOR OUR OWN. CONGESTION ON THE FREQ WAS A FACTOR. SUPPLEMENTAL INFO FROM ACN 501826: ON THE ABOVE DATE I WAS SERVING AS FO ON ACR Y FROM BOS TO ROC. WE HAD RECEIVED A CLRNC TO TAXI KILO; CHARLIE; DELTA TO RWY 27. HOLD SHORT OF RWY 33 AT DELTA. 'ATC INFORMED US THAT RWY 33L AT GOLF WAS AVAILABLE FOR TKOF ONLY FOR ANOTHER 5 MIN.' THE CAPT WAS THE PF SO HE STATED HE WOULD LIKE TO ACCEPT AN INTXN TKOF RWY 33L AT GOLF AND I PROCEEDED TO REVIEW THE TKOF DATA FOR RWY 33L AT GOLF PROVIDED IN THE MANUAL. WE WERE INSTRUCTED TO 'HOLD SHORT RWY 33L AT GOLF.' AFTER WAITING THERE WE RECEIVED INSTRUCTIONS TO TAXI INTO POS AND HOLD. THE INSTRUCTIONS WERE REPEATED BACK TO ATC. 'POS HOLD RWY 33L AT GOLF. THE CAPT CALLED FOR THE BEFORE TKOF CHKLIST; RELEASED THE BRAKES; AND I BEGAN THE BEFORE TKOF CHKLIST. THE CAPT INQUIRED 'WE'RE CLRED FOR TKOF?' AND I SAID 'NO POS AND HOLD.' AT THIS INSTANT I SAW THE B757 ON TKOF ROLL. ATC INSTRUCTED 'ACR Y STOP.' WE WERE PAST THE HOLD SHORT BARS AND SHORT OF THE RWY EDGE LINE BY APPROX 30 FT. WE WERE TOLD TO EXIT THE RWY BY MAKING A U TURN EXIT THE INTXN AND THEN SUBSEQUENTLY GIVEN CLRNC TO DEPART FROM THE SAME INTXN. I WAS NOT ABLE TO SEE THE ACFT; WHICH WAS DEPARTING FULL LENGTH RWY 33L FROM RWY 33L GOLF INTXN; UNTIL IT WAS ROLLING TOWARDS US; DOWN THE RWY. HOWEVER; I DID INCORPORATE A 'CLR RIGHT' CHK WITH THE TKOF FLOW. THE B757 CAME INTO MY VIEW 1 SEC BEFORE ATC INSTRUCTED OUR CREW TO 'STOP.' THIS WAS JUST AS WE HAD CROSSED THE HOLD SHORT BARS. VFR CONDITIONS PREVAILED. CREW WAS FAMILIAR WITH OPS AT LOGAN ARPT. ATC ACTIVITY WAS HEAVY AT THE TIME OF THE INCIDENT. CALLBACK CONVERSATION WITH RPTR ACN 502960 REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE WAS CALLED BY THE TWR SUPERVISOR ON THE TELEPHONE SOMETIME AFTER THE INCIDENT. AFTER PLAYING THE TAPES THE SUPERVISOR SAID ACR X WAS HEARD TO ACKNOWLEDGE TKOF CLRNC FOLLOWED BY A GARBLED XMISSION. THE RPTR SAID NO ACTION HAS BEEN TAKEN BY THE FAA AT THIS TIME. CALLBACK CONVERSATION WITH RPTR ACN 503081 REVEALED THE FOLLOWING INFO: RPTR STATED HE WAS THE PF AND OBSERVED THE SAAB ACFT IMMEDIATELY AFTER STARTING THE TKOF. WHILE UNDERWAY; HE SAID IT APPEARED THAT THE SAAB WAS MOVING TOWARD THE RWY. HE SAID HE WAS USING RUDDER CTL FOR STEERING AND MOVED APPROX FIVE FT RIGHT OF CENTERLINE FOR AN ADDED MARGIN OF SAFETY. THE RPTR VERIFIED THAT HIS ACFT WAS A B757 WITH A WING SPAN OF ABOUT 125 FT AND THAT THE WIDTH OF RWY 33L IS 150 FT. CALLBACK CONVERSATION WITH RPTR ACN 501972 REVEALED THE FOLLOWING INFO: RPTR STATED THAT EVEN THOUGH THEY ACCEPTED THE INTXN TKOF; THEY WERE UNEASY ABOUT IT BECSAUSE IT WAS AFTER DUSK. HE ALSO SAID THAT THEY SHOULD HAVE CONFIRMED THEIR TAXI CLRNC.