Narrative:

During arrival into atlanta on sinca arrival (atl 128 degree radial), we crossed the husky fix at 14000 ft and received further descent to 12000 ft. I was anticipating clearance to downwind heading of approximately 270 degrees further descent to 7000 ft. Prior to leveling at 12000 ft, ATC cleared us for further descent to what I heard as 'descend to 7000 ft' and I entered 7000 ft in the altitude window on the autoplt panel (autoplt was on) as the first officer acknowledged and read back to ATC as 'descend to 7000 ft.' as we descended through 10500 ft, we saw a climbing departure aircraft visually after a TCASII alert. Approach controller queried us for our altitude and first officer (PNF) responded with 'descending to 7000 ft, traffic in sight.' controller responded with 'climb to 11000 ft, maintain visual separation.' we climbed to 11000 ft, and shortly later, received clearance to 'turn to 275 degrees, descend to 7000 ft.' I believe this occurrence was a hearback/readback problem coupled with similar sounding altitudes of seven/eleven. To prevent recurrence, I believe in this case where eleven and seven thousand ft altitude clrncs routinely come subsequently to each other, that the eleven thousand ft clearance should be given as 'descend to one-one eleven thousand' to further distinguish it from the 'descend to 7000 ft' clearance.

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Original NASA ASRS Text

Title: B757 LNDG AT ATL ANTICIPATES ALT CLRNC AND DSNDS BELOW ASSIGNED ALT.

Narrative: DURING ARR INTO ATLANTA ON SINCA ARR (ATL 128 DEG RADIAL), WE CROSSED THE HUSKY FIX AT 14000 FT AND RECEIVED FURTHER DSCNT TO 12000 FT. I WAS ANTICIPATING CLRNC TO DOWNWIND HDG OF APPROX 270 DEGS FURTHER DSCNT TO 7000 FT. PRIOR TO LEVELING AT 12000 FT, ATC CLRED US FOR FURTHER DSCNT TO WHAT I HEARD AS 'DSND TO 7000 FT' AND I ENTERED 7000 FT IN THE ALT WINDOW ON THE AUTOPLT PANEL (AUTOPLT WAS ON) AS THE FO ACKNOWLEDGED AND READ BACK TO ATC AS 'DSND TO 7000 FT.' AS WE DSNDED THROUGH 10500 FT, WE SAW A CLBING DEP ACFT VISUALLY AFTER A TCASII ALERT. APCH CTLR QUERIED US FOR OUR ALT AND FO (PNF) RESPONDED WITH 'DSNDING TO 7000 FT, TFC IN SIGHT.' CTLR RESPONDED WITH 'CLB TO 11000 FT, MAINTAIN VISUAL SEPARATION.' WE CLBED TO 11000 FT, AND SHORTLY LATER, RECEIVED CLRNC TO 'TURN TO 275 DEGS, DSND TO 7000 FT.' I BELIEVE THIS OCCURRENCE WAS A HEARBACK/READBACK PROB COUPLED WITH SIMILAR SOUNDING ALTS OF SEVEN/ELEVEN. TO PREVENT RECURRENCE, I BELIEVE IN THIS CASE WHERE ELEVEN AND SEVEN THOUSAND FT ALT CLRNCS ROUTINELY COME SUBSEQUENTLY TO EACH OTHER, THAT THE ELEVEN THOUSAND FT CLRNC SHOULD BE GIVEN AS 'DSND TO ONE-ONE ELEVEN THOUSAND' TO FURTHER DISTINGUISH IT FROM THE 'DSND TO 7000 FT' CLRNC.

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.