Narrative:

Checked in with second potomac approach frequency 125.8 at 6000 ft. Potomac acknowledged with 'roger.' about 1 min later; we got a 'traffic' from the TCAS. Traffic was at 1 O'clock position; 1200 ft above and descending. We watched the traffic on the TCAS display descend through 1000 ft relative altitude with a constant bearing. We were IMC in clouds. Within a few seconds; the TA became an RA with 'monitor vertical speed' command and vertical speed indicator showing red from 0 up to 2000 FPM climb. We watched the relative altitude decrease to 300 ft and the target merged with our aircraft symbol. The TCAS then commanded 'descend' with green vertical speed at 1500 FPM to 2500 FPM. During the escape maneuver; potomac called and cleared us to 3000 ft. I advised him that we had an RA and were already in a descent. I think the controller might have been overloaded. Usually when checking in at 6000 ft you are asked to descend to 5000 ft or 4000 ft. There were thunderstorms throughout the area all day. I can't remember if it was this controller or the previous one; but he was distraction with a GA pilot trying to get into a local airport. They were discussing holding or trying an approach.

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Original NASA ASRS Text

Title: IFR ACR EXPERIENCED TCAS RA CONFLICT EVENT AT 6000 INBOUND TO IAD; LISTED BY FAA AS OPERROR.

Narrative: CHKED IN WITH SECOND POTOMAC APCH FREQ 125.8 AT 6000 FT. POTOMAC ACKNOWLEDGED WITH 'ROGER.' ABOUT 1 MIN LATER; WE GOT A 'TFC' FROM THE TCAS. TFC WAS AT 1 O'CLOCK POS; 1200 FT ABOVE AND DSNDING. WE WATCHED THE TFC ON THE TCAS DISPLAY DSND THROUGH 1000 FT RELATIVE ALT WITH A CONSTANT BEARING. WE WERE IMC IN CLOUDS. WITHIN A FEW SECONDS; THE TA BECAME AN RA WITH 'MONITOR VERT SPD' COMMAND AND VERT SPD INDICATOR SHOWING RED FROM 0 UP TO 2000 FPM CLB. WE WATCHED THE RELATIVE ALT DECREASE TO 300 FT AND THE TARGET MERGED WITH OUR ACFT SYMBOL. THE TCAS THEN COMMANDED 'DSND' WITH GREEN VERT SPD AT 1500 FPM TO 2500 FPM. DURING THE ESCAPE MANEUVER; POTOMAC CALLED AND CLRED US TO 3000 FT. I ADVISED HIM THAT WE HAD AN RA AND WERE ALREADY IN A DSCNT. I THINK THE CTLR MIGHT HAVE BEEN OVERLOADED. USUALLY WHEN CHKING IN AT 6000 FT YOU ARE ASKED TO DSND TO 5000 FT OR 4000 FT. THERE WERE TSTMS THROUGHOUT THE AREA ALL DAY. I CAN'T REMEMBER IF IT WAS THIS CTLR OR THE PREVIOUS ONE; BUT HE WAS DISTR WITH A GA PLT TRYING TO GET INTO A LCL ARPT. THEY WERE DISCUSSING HOLDING OR TRYING AN APCH.

Data retrieved from NASA's ASRS site as of May 2009 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.