Narrative:

While approaching den airport for landing, an incorrect altitude assignment was apparently issued by ATC. We had received a handoff from ZDV who had assigned 17000 ft. Upon check-in, den approach assigned a lower altitude of 15000 ft. Soon afterward we were given a heading of 080 degrees for traffic and a new altitude assignment of 12000 ft. While descending to 12000 ft, we were given a heading of 150 degrees. At this time, I left the ATC frequency to contact our company operations on a second radio. Simultaneous with my call to operations, we received a TCASII TA for traffic approaching approximately 3 mi from our left and 400 ft below. We were descending through 12400 ft. At the same time I could hear ATC advising us our assigned altitude was 13000 ft and to climb and maintain 13000 ft. I spotted the traffic causing the TA and switched back to the ATC frequency. Again, we were assigned 13000 ft, and advised that our last assigned altitude had been 12000 ft, to which the controller replied had never assigned. We were handed off to the next controller and the balance of the flight was uneventful. On this particular flight we had a pilot occupying our cockpit jump seat. On conferring with him on the ground, we found he'd also heard the 12000 ft assignment. A subsequent telephone call from den TRACON revealed they had reviewed the recording and found that the controller had indeed assigned 12000 ft.

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Original NASA ASRS Text

Title: WHILE DSNDING IN DEN TRACON AIRSPACE, AN ACR D328 FLC EXECUTES EVASIVE TCASII MANEUVER REACTING TO TFC BELOW, CLBING AND CONVERGING. FOLLOW-UP CONVERSATION WITH TRACON SUPVR REVEALS CTLR INCORRECTLY ASSIGNED AN ALT THAT WOULD CONFLICT WITH CLBING TFC.

Narrative: WHILE APCHING DEN ARPT FOR LNDG, AN INCORRECT ALT ASSIGNMENT WAS APPARENTLY ISSUED BY ATC. WE HAD RECEIVED A HDOF FROM ZDV WHO HAD ASSIGNED 17000 FT. UPON CHK-IN, DEN APCH ASSIGNED A LOWER ALT OF 15000 FT. SOON AFTERWARD WE WERE GIVEN A HDG OF 080 DEGS FOR TFC AND A NEW ALT ASSIGNMENT OF 12000 FT. WHILE DSNDING TO 12000 FT, WE WERE GIVEN A HDG OF 150 DEGS. AT THIS TIME, I LEFT THE ATC FREQ TO CONTACT OUR COMPANY OPS ON A SECOND RADIO. SIMULTANEOUS WITH MY CALL TO OPS, WE RECEIVED A TCASII TA FOR TFC APCHING APPROX 3 MI FROM OUR L AND 400 FT BELOW. WE WERE DSNDING THROUGH 12400 FT. AT THE SAME TIME I COULD HEAR ATC ADVISING US OUR ASSIGNED ALT WAS 13000 FT AND TO CLB AND MAINTAIN 13000 FT. I SPOTTED THE TFC CAUSING THE TA AND SWITCHED BACK TO THE ATC FREQ. AGAIN, WE WERE ASSIGNED 13000 FT, AND ADVISED THAT OUR LAST ASSIGNED ALT HAD BEEN 12000 FT, TO WHICH THE CTLR REPLIED HAD NEVER ASSIGNED. WE WERE HANDED OFF TO THE NEXT CTLR AND THE BAL OF THE FLT WAS UNEVENTFUL. ON THIS PARTICULAR FLT WE HAD A PLT OCCUPYING OUR COCKPIT JUMP SEAT. ON CONFERRING WITH HIM ON THE GND, WE FOUND HE'D ALSO HEARD THE 12000 FT ASSIGNMENT. A SUBSEQUENT TELEPHONE CALL FROM DEN TRACON REVEALED THEY HAD REVIEWED THE RECORDING AND FOUND THAT THE CTLR HAD INDEED ASSIGNED 12000 FT.

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.