Narrative:

Approaching armel VOR from the west inbound to dca controller gave us a clearance to turn left to 360 degrees and level at 13000'. The previous clearance was to 11000' and we were at 12500'. We stated we were at 12500' and immediately began a climb to 13000'. Very shortly thereafter an air carrier Q medium large transport passed directly beneath us at 12000'. The air carrier Q crew questioned our altitude and the controller said we were at 13000'. The controller said he had given us the heading earlier. We heard a garble transmission re: a heading. When we asked who that clearance was for, we received no reply. When controllers and pilots make statements or issue clrncs, it is extremely important to listen for a proper acknowledgement.

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Original NASA ASRS Text

Title: CLOSE PROX LESS THAN STANDARD SEPARATION ACR-LGT ACR-MLG OPPOSITE DIRECTION WORKING IAD APCH CTL.

Narrative: APCHING ARMEL VOR FROM THE W INBND TO DCA CTLR GAVE US A CLRNC TO TURN LEFT TO 360 DEGS AND LEVEL AT 13000'. THE PREVIOUS CLRNC WAS TO 11000' AND WE WERE AT 12500'. WE STATED WE WERE AT 12500' AND IMMEDIATELY BEGAN A CLB TO 13000'. VERY SHORTLY THEREAFTER AN ACR Q MLG PASSED DIRECTLY BENEATH US AT 12000'. THE ACR Q CREW QUESTIONED OUR ALT AND THE CTLR SAID WE WERE AT 13000'. THE CTLR SAID HE HAD GIVEN US THE HDG EARLIER. WE HEARD A GARBLE XMISSION RE: A HDG. WHEN WE ASKED WHO THAT CLRNC WAS FOR, WE RECEIVED NO REPLY. WHEN CTLRS AND PLTS MAKE STATEMENTS OR ISSUE CLRNCS, IT IS EXTREMELY IMPORTANT TO LISTEN FOR A PROPER ACKNOWLEDGEMENT.

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.