Narrative:

On arrival into stl, we are normally cleared from 8000 ft down to 7000 ft along this portion of the rivers 2 arrival into stl. ATC instead cleared us additionally down to 5000 ft from our current altitude of 7000 ft. We thought the descent clearance unusual, but ATC was very busy, and our readback brought no additional comment. We began our descent from 7000 ft to 5000 ft in VMC. As we passed through 5500 ft, ATC suddenly asked, 'air carrier xx, are you descending?' I said, 'yes, out of 5400 ft for 5000 ft. ATC said he never gave us this altitude and directed to climb back to 7000 ft 'immediately.' I told him we had received the clearance but would climb back to 7000 ft. The flight proceeded normally after that. My first officer and I discussed what had happened and why. Both of us remembered the altitude clearance, we had read it back to each other, the altitude was set in the alerter, and we had read it back to ATC without getting a correction. Later, my first officer remembered that ATC had had to tell an 'air carrier XXX' twice to descend as instructed. The similarities in call signs (XXX versus xx) convinces us that ATC meant to call XXX, not our flight. If a clearance is unusual, a mild query to ATC might have cleared up the confusion.

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Original NASA ASRS Text

Title: SIMILAR CALL SIGNS, INCOMPLETE CALL SIGNS, HEARBACK PROBS EQUAL ALT DEV NEAR CSX.

Narrative: ON ARR INTO STL, WE ARE NORMALLY CLRED FROM 8000 FT DOWN TO 7000 FT ALONG THIS PORTION OF THE RIVERS 2 ARR INTO STL. ATC INSTEAD CLRED US ADDITIONALLY DOWN TO 5000 FT FROM OUR CURRENT ALT OF 7000 FT. WE THOUGHT THE DSCNT CLRNC UNUSUAL, BUT ATC WAS VERY BUSY, AND OUR READBACK BROUGHT NO ADDITIONAL COMMENT. WE BEGAN OUR DSCNT FROM 7000 FT TO 5000 FT IN VMC. AS WE PASSED THROUGH 5500 FT, ATC SUDDENLY ASKED, 'ACR XX, ARE YOU DSNDING?' I SAID, 'YES, OUT OF 5400 FT FOR 5000 FT. ATC SAID HE NEVER GAVE US THIS ALT AND DIRECTED TO CLB BACK TO 7000 FT 'IMMEDIATELY.' I TOLD HIM WE HAD RECEIVED THE CLRNC BUT WOULD CLB BACK TO 7000 FT. THE FLT PROCEEDED NORMALLY AFTER THAT. MY FO AND I DISCUSSED WHAT HAD HAPPENED AND WHY. BOTH OF US REMEMBERED THE ALT CLRNC, WE HAD READ IT BACK TO EACH OTHER, THE ALT WAS SET IN THE ALERTER, AND WE HAD READ IT BACK TO ATC WITHOUT GETTING A CORRECTION. LATER, MY FO REMEMBERED THAT ATC HAD HAD TO TELL AN 'ACR XXX' TWICE TO DSND AS INSTRUCTED. THE SIMILARITIES IN CALL SIGNS (XXX VERSUS XX) CONVINCES US THAT ATC MEANT TO CALL XXX, NOT OUR FLT. IF A CLRNC IS UNUSUAL, A MILD QUERY TO ATC MIGHT HAVE CLRED UP THE CONFUSION.

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.