Narrative:

At the end of a very long day on the last flight from bos to dca, we were cleared to taxi to runway 9 at bos. We checked our weight and found that we could not use runway 9 and were directed to taxi to runway 4R via outer and bravo from our gate #8. We ran the checklist and I got the airport diagram out as I was unfamiliar with this route and I was very concerned about making a runway incursion with this route. The first officer was going to make the takeoff and when he briefed the departure, I believe he said 'runway heading to 4 mi, left to 090 degree'. I had not checked the departure after the runway change. I thought that he said 'runway heading to 400' (the normal altitude required prior to initiating a turn) turn to 090'. Just prior to taking the runway, I again stated that the departure was to maintain runway heading to 400' and then right to 090 degree. The first officer did not correct me and we took off and at 400' turned to 090. Upon initial call to departure, I informed them we were leaving 800' in a right turn to 090 degree. The controller asked me if we had been assigned the turn. I replied that was my understanding and looked to the copilot for confirmation since I was not in the cockpit during the clearance copying. Upon checking I found that the SID said to maintain runway heading until the bos 4 DME and then turn to the 090 heading. Contributing to the misunderstanding was the fact that I had passed through bos several times on this trip and we had used runway 22 for departure every time which calls for runway heading (400') and a turn to 090 degree. I heard the copilot say what I expected him to say regardless of what he really said. Once again I learn to reset everything and reread the departure after a runway change. I allowed us to become distracted by the weight and balance and then the unusual taxi route to the runway.

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Original NASA ASRS Text

Title: ACR FLT DEVIATED FROM SID IN TURNING TOO SOON.

Narrative: AT THE END OF A VERY LONG DAY ON THE LAST FLT FROM BOS TO DCA, WE WERE CLRED TO TAXI TO RWY 9 AT BOS. WE CHECKED OUR WEIGHT AND FOUND THAT WE COULD NOT USE RWY 9 AND WERE DIRECTED TO TAXI TO RWY 4R VIA OUTER AND BRAVO FROM OUR GATE #8. WE RAN THE CHECKLIST AND I GOT THE ARPT DIAGRAM OUT AS I WAS UNFAMILIAR WITH THIS ROUTE AND I WAS VERY CONCERNED ABOUT MAKING A RWY INCURSION WITH THIS ROUTE. THE F/O WAS GOING TO MAKE THE TKOF AND WHEN HE BRIEFED THE DEP, I BELIEVE HE SAID 'RWY HDG TO 4 MI, LEFT TO 090 DEG'. I HAD NOT CHECKED THE DEP AFTER THE RWY CHANGE. I THOUGHT THAT HE SAID 'RWY HDG TO 400' (THE NORMAL ALT REQUIRED PRIOR TO INITIATING A TURN) TURN TO 090'. JUST PRIOR TO TAKING THE RWY, I AGAIN STATED THAT THE DEP WAS TO MAINTAIN RWY HDG TO 400' AND THEN RIGHT TO 090 DEG. THE F/O DID NOT CORRECT ME AND WE TOOK OFF AND AT 400' TURNED TO 090. UPON INITIAL CALL TO DEP, I INFORMED THEM WE WERE LEAVING 800' IN A RIGHT TURN TO 090 DEG. THE CTLR ASKED ME IF WE HAD BEEN ASSIGNED THE TURN. I REPLIED THAT WAS MY UNDERSTANDING AND LOOKED TO THE COPLT FOR CONFIRMATION SINCE I WAS NOT IN THE COCKPIT DURING THE CLRNC COPYING. UPON CHECKING I FOUND THAT THE SID SAID TO MAINTAIN RWY HDG UNTIL THE BOS 4 DME AND THEN TURN TO THE 090 HDG. CONTRIBUTING TO THE MISUNDERSTANDING WAS THE FACT THAT I HAD PASSED THROUGH BOS SEVERAL TIMES ON THIS TRIP AND WE HAD USED RWY 22 FOR DEP EVERY TIME WHICH CALLS FOR RWY HDG (400') AND A TURN TO 090 DEG. I HEARD THE COPLT SAY WHAT I EXPECTED HIM TO SAY REGARDLESS OF WHAT HE REALLY SAID. ONCE AGAIN I LEARN TO RESET EVERYTHING AND REREAD THE DEP AFTER A RWY CHANGE. I ALLOWED US TO BECOME DISTRACTED BY THE WEIGHT AND BALANCE AND THEN THE UNUSUAL TAXI ROUTE TO THE RWY.

Data retrieved from NASA's ASRS site as of August 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.