Narrative:

I was returning to the cockpit after a short trip to the lavatory. Upon entering, I heard a TCASII alert, 'traffic, traffic.' as I was taking my seat, I observed a target on the edge of the TCASII screen at the 12:30 O'clock position, opposite direction, range approximately 6 mi. The tag on the target indicated that it was 1000 ft below us (level at FL310). The first officer had begun a descent from FL330 to FL290. I was looking for the traffic visually when the TCASII RA sounded 'climb, climb.' the first officer began to climb the aircraft. I observed the target on TCASII at 900 ft below us and about 2-3 mi. It was just after that when I was able to acquire the other aircraft visually. We were climbing when the aircraft passed by our right side. We returned to FL330. It was later determined that the first officer accepted a descent clearance for a company flight xay, and ATC missed the readback verification. Flight xay did not acknowledge the clearance and did not begin a descent. I have notified our company, explaining the potentially serious problems that can result with so many similar sounding flight numbers such as we have at this time. My recommendation is that there never be 2 aircraft scheduled to be in the same airspace with 2 of the 3 flight number digits the same.

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Original NASA ASRS Text

Title: AN MD80 FLC RECEIVED A DSCNT CLRNC MEANT FOR A SIMILAR CALL SIGN COMPANY ACFT BELOW THEM. LOSS OF SEPARATION OCCURRED WHEN THE RPTR STARTED THE DSCNT AND THE OTHER ACFT REMAINED AT CRUISE ALT. THE CTLR DID NOT CATCH THE READBACK ERROR BY THE PLT. THE DSNDING ACFT RECEIVED A TCASII RA AND BEGAN A CLB TO RESOLVE THE ERROR.

Narrative: I WAS RETURNING TO THE COCKPIT AFTER A SHORT TRIP TO THE LAVATORY. UPON ENTERING, I HEARD A TCASII ALERT, 'TFC, TFC.' AS I WAS TAKING MY SEAT, I OBSERVED A TARGET ON THE EDGE OF THE TCASII SCREEN AT THE 12:30 O'CLOCK POS, OPPOSITE DIRECTION, RANGE APPROX 6 MI. THE TAG ON THE TARGET INDICATED THAT IT WAS 1000 FT BELOW US (LEVEL AT FL310). THE FO HAD BEGUN A DSCNT FROM FL330 TO FL290. I WAS LOOKING FOR THE TFC VISUALLY WHEN THE TCASII RA SOUNDED 'CLB, CLB.' THE FO BEGAN TO CLB THE ACFT. I OBSERVED THE TARGET ON TCASII AT 900 FT BELOW US AND ABOUT 2-3 MI. IT WAS JUST AFTER THAT WHEN I WAS ABLE TO ACQUIRE THE OTHER ACFT VISUALLY. WE WERE CLBING WHEN THE ACFT PASSED BY OUR R SIDE. WE RETURNED TO FL330. IT WAS LATER DETERMINED THAT THE FO ACCEPTED A DSCNT CLRNC FOR A COMPANY FLT XAY, AND ATC MISSED THE READBACK VERIFICATION. FLT XAY DID NOT ACKNOWLEDGE THE CLRNC AND DID NOT BEGIN A DSCNT. I HAVE NOTIFIED OUR COMPANY, EXPLAINING THE POTENTIALLY SERIOUS PROBS THAT CAN RESULT WITH SO MANY SIMILAR SOUNDING FLT NUMBERS SUCH AS WE HAVE AT THIS TIME. MY RECOMMENDATION IS THAT THERE NEVER BE 2 ACFT SCHEDULED TO BE IN THE SAME AIRSPACE WITH 2 OF THE 3 FLT NUMBER DIGITS THE SAME.

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.