Narrative:

We were operating as air carrier X. When we first entered stl approach control, same air carrier aircraft Y, timed to arrive at stl within 2 mins of our scheduled arrival, accepted our heading clearance. Approach corrected aircraft Y. At the point in the arrival where we (aircraft X) would expect an approach clearance, ATC advised air carrier X to maintain at or above 3500 ft in the river, 170 KTS to the OM, cleared for visual approach to runway 30R at stl. We (aircraft X) repeated the entire set of instructions and clearance. At an altitude of 4300 ft, ATC queried us as to our current altitude. We advised 4300 ft. ATC advised us to stop descent, because we were following instructions intended for aircraft Y. ATC then gave aircraft Y the clearance we had been given and 3 mins later told air carrier X to resume our previous visual approach to runway 30R. Supplemental information from acn 427997: a clearance was given, which I believe to my flight. My first officer read back the clearance, which included the option of a lower altitude and completed the transmission. No response was given by the approach controller and I began a descent from 5000 ft. The factors which caused this discrepancy are obvious. Flight numbers very similar to one another, and lack of attention during the readback helped to create this confusion.

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Original NASA ASRS Text

Title: ACR BA41 FLC CLRNCS BECOME CONFUSED WITH COMPANY ACFT, WITH SIMILAR SOUNDING CALL SIGN, BOTH INBOUND TO STL ARPT.

Narrative: WE WERE OPERATING AS ACR X. WHEN WE FIRST ENTERED STL APCH CTL, SAME ACR ACFT Y, TIMED TO ARRIVE AT STL WITHIN 2 MINS OF OUR SCHEDULED ARR, ACCEPTED OUR HDG CLRNC. APCH CORRECTED ACFT Y. AT THE POINT IN THE ARR WHERE WE (ACFT X) WOULD EXPECT AN APCH CLRNC, ATC ADVISED ACR X TO MAINTAIN AT OR ABOVE 3500 FT IN THE RIVER, 170 KTS TO THE OM, CLRED FOR VISUAL APCH TO RWY 30R AT STL. WE (ACFT X) REPEATED THE ENTIRE SET OF INSTRUCTIONS AND CLRNC. AT AN ALT OF 4300 FT, ATC QUERIED US AS TO OUR CURRENT ALT. WE ADVISED 4300 FT. ATC ADVISED US TO STOP DSCNT, BECAUSE WE WERE FOLLOWING INSTRUCTIONS INTENDED FOR ACFT Y. ATC THEN GAVE ACFT Y THE CLRNC WE HAD BEEN GIVEN AND 3 MINS LATER TOLD ACR X TO RESUME OUR PREVIOUS VISUAL APCH TO RWY 30R. SUPPLEMENTAL INFO FROM ACN 427997: A CLRNC WAS GIVEN, WHICH I BELIEVE TO MY FLT. MY FO READ BACK THE CLRNC, WHICH INCLUDED THE OPTION OF A LOWER ALT AND COMPLETED THE XMISSION. NO RESPONSE WAS GIVEN BY THE APCH CTLR AND I BEGAN A DSCNT FROM 5000 FT. THE FACTORS WHICH CAUSED THIS DISCREPANCY ARE OBVIOUS. FLT NUMBERS VERY SIMILAR TO ONE ANOTHER, AND LACK OF ATTN DURING THE READBACK HELPED TO CREATE THIS 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.