Narrative:

Descent to bwi at 11000 ft, first officer flying, had just made PA seating the flight attendants. I was monitoring communication #1 during my PA and returned halfway through their instructions. I understood bwi to say slow to 270 KTS, then descend to 6000 ft. I slowed, then began to descend on course. The captain switched off to coordinate with operations and maintenance. Descending through 10000 ft, bwi approach asked me if I was heading 270 degrees yet. I asked if they wanted me flying 270 degree heading, and they said yes. I began the turn, then they said forget the turn, descend to 5000 ft and expedite through 6000 ft, turn left to 180 degrees. In the turning, descending, and expediting the descent, I went through 10 KTS still at 270 degree heading. At about 8 KTS, captain returned to frequency, and I told him what he missed. Baltimore didn't say any more. Supplemental information from acn 573563: we were flying the FMS on the programmed flight plan (at 11000 ft) into bwi, and as we made the last turn direct to the VOR, ATC gave us a 270 degree heading and a descent to 6000 ft. When I came back on frequency, I looked up and we were descending through +/-7000 and were indicating 275 KTS. I questioned the first officer, and he told me that he did not understand the clearance to 270 degrees. My mistake was not to monitor the PF closer in compliance with an assigned clearance. I misinterped that FMS turn as compliance with the assigned heading.

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Original NASA ASRS Text

Title: B737-700 FO MISTAKES BWI HDG CHANGE WITH ALT DSCNT CLRNC FOR SPD CLRNC, NO HDG CHANGE.

Narrative: DSCNT TO BWI AT 11000 FT, FO FLYING, HAD JUST MADE PA SEATING THE FLT ATTENDANTS. I WAS MONITORING COM #1 DURING MY PA AND RETURNED HALFWAY THROUGH THEIR INSTRUCTIONS. I UNDERSTOOD BWI TO SAY SLOW TO 270 KTS, THEN DSND TO 6000 FT. I SLOWED, THEN BEGAN TO DSND ON COURSE. THE CAPT SWITCHED OFF TO COORDINATE WITH OPS AND MAINT. DSNDING THROUGH 10000 FT, BWI APCH ASKED ME IF I WAS HDG 270 DEGS YET. I ASKED IF THEY WANTED ME FLYING 270 DEG HDG, AND THEY SAID YES. I BEGAN THE TURN, THEN THEY SAID FORGET THE TURN, DSND TO 5000 FT AND EXPEDITE THROUGH 6000 FT, TURN L TO 180 DEGS. IN THE TURNING, DSNDING, AND EXPEDITING THE DSCNT, I WENT THROUGH 10 KTS STILL AT 270 DEG HDG. AT ABOUT 8 KTS, CAPT RETURNED TO FREQ, AND I TOLD HIM WHAT HE MISSED. BALTIMORE DIDN'T SAY ANY MORE. SUPPLEMENTAL INFO FROM ACN 573563: WE WERE FLYING THE FMS ON THE PROGRAMMED FLT PLAN (AT 11000 FT) INTO BWI, AND AS WE MADE THE LAST TURN DIRECT TO THE VOR, ATC GAVE US A 270 DEG HDG AND A DSCNT TO 6000 FT. WHEN I CAME BACK ON FREQ, I LOOKED UP AND WE WERE DSNDING THROUGH +/-7000 AND WERE INDICATING 275 KTS. I QUESTIONED THE FO, AND HE TOLD ME THAT HE DID NOT UNDERSTAND THE CLRNC TO 270 DEGS. MY MISTAKE WAS NOT TO MONITOR THE PF CLOSER IN COMPLIANCE WITH AN ASSIGNED CLRNC. I MISINTERPED THAT FMS TURN AS COMPLIANCE WITH THE ASSIGNED HDG.

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.