Narrative:

We were level at 8000' during an intermediate phase of the climb out on the way to txk. Our flight, air carrier X. Just ahead of us there was a metropolitan 851 and another aircraft with a somewhat similar call sign all on the same frequency. I was PNF when at a point approximately 25 mi out of slr ATC with a clearance to 13000'. He used a call sign that was close to, but not quite ours. Then ATC called twice more in quick succession with clearance to 13000'. Each time the flight call sign was a little different, but the third call was definitely air carrier X. I read it back then, stating very clearly air carrier X climbing to 13000'. I remarked to the first officer that ATC was having trouble with the similar call signs today. While climbing through about 9000' I heard ATC call for air carrier X to descend to 8000'. Having just been cleared to 13000' I though ATC was mistaking a call sign again and I didn't answer. A few seconds later a second voice, a supervisor I suppose, called 'air carrier X, descend immediately to 8000, left turn to 040 degrees.' I acknowledged and we implemented this command immediately. No further information was forthcoming, but we scanned the skies. My first officer saw what we believed to be a military spc off to our right. Now this aircraft was nowhere near enough to us to be anything like what I would call a near miss, but apparently ATC's standards were exceeded. Shortly after descending to 8000' and turning to 040 degrees I, being very nervous at this time just in case I had made a mistake, asked ATC to confirm that air carrier X had been previously cleared to 13000'. ATC said yes, with no further comment. Shortly thereafter we were reclred to 13000' and direct to slf VOR on course. I'm not sure exactly what happened. It seemed ATC was having some trouble with similar radio call signs and further seemed to be having trouble communicating with the aircraft that we think was a military spc Y. I don't know if ATC gave us the wrong clearance or the other aircraft or if he was just not where he was supposed to be, but I'm sure the similar call signs were at least a contributing factor. We have trouble with similar radio call signs all the time.

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Original NASA ASRS Text

Title: ACR X HAD LESS THAN STANDARD SEPARATION FROM MIL SPC Y. SYSTEM ERROR.

Narrative: WE WERE LEVEL AT 8000' DURING AN INTERMEDIATE PHASE OF THE CLBOUT ON THE WAY TO TXK. OUR FLT, ACR X. JUST AHEAD OF US THERE WAS A METRO 851 AND ANOTHER ACFT WITH A SOMEWHAT SIMILAR CALL SIGN ALL ON THE SAME FREQ. I WAS PNF WHEN AT A POINT APPROX 25 MI OUT OF SLR ATC WITH A CLRNC TO 13000'. HE USED A CALL SIGN THAT WAS CLOSE TO, BUT NOT QUITE OURS. THEN ATC CALLED TWICE MORE IN QUICK SUCCESSION WITH CLRNC TO 13000'. EACH TIME THE FLT CALL SIGN WAS A LITTLE DIFFERENT, BUT THE THIRD CALL WAS DEFINITELY ACR X. I READ IT BACK THEN, STATING VERY CLEARLY ACR X CLBING TO 13000'. I REMARKED TO THE F/O THAT ATC WAS HAVING TROUBLE WITH THE SIMILAR CALL SIGNS TODAY. WHILE CLBING THROUGH ABOUT 9000' I HEARD ATC CALL FOR ACR X TO DSND TO 8000'. HAVING JUST BEEN CLRED TO 13000' I THOUGH ATC WAS MISTAKING A CALL SIGN AGAIN AND I DIDN'T ANSWER. A FEW SECS LATER A SECOND VOICE, A SUPVR I SUPPOSE, CALLED 'ACR X, DSND IMMEDIATELY TO 8000, LEFT TURN TO 040 DEGS.' I ACKNOWLEDGED AND WE IMPLEMENTED THIS COMMAND IMMEDIATELY. NO FURTHER INFO WAS FORTHCOMING, BUT WE SCANNED THE SKIES. MY F/O SAW WHAT WE BELIEVED TO BE A MIL SPC OFF TO OUR RIGHT. NOW THIS ACFT WAS NOWHERE NEAR ENOUGH TO US TO BE ANYTHING LIKE WHAT I WOULD CALL A NEAR MISS, BUT APPARENTLY ATC'S STANDARDS WERE EXCEEDED. SHORTLY AFTER DSNDING TO 8000' AND TURNING TO 040 DEGS I, BEING VERY NERVOUS AT THIS TIME JUST IN CASE I HAD MADE A MISTAKE, ASKED ATC TO CONFIRM THAT ACR X HAD BEEN PREVIOUSLY CLRED TO 13000'. ATC SAID YES, WITH NO FURTHER COMMENT. SHORTLY THEREAFTER WE WERE RECLRED TO 13000' AND DIRECT TO SLF VOR ON COURSE. I'M NOT SURE EXACTLY WHAT HAPPENED. IT SEEMED ATC WAS HAVING SOME TROUBLE WITH SIMILAR RADIO CALL SIGNS AND FURTHER SEEMED TO BE HAVING TROUBLE COMMUNICATING WITH THE ACFT THAT WE THINK WAS A MIL SPC Y. I DON'T KNOW IF ATC GAVE US THE WRONG CLRNC OR THE OTHER ACFT OR IF HE WAS JUST NOT WHERE HE WAS SUPPOSED TO BE, BUT I'M SURE THE SIMILAR CALL SIGNS WERE AT LEAST A CONTRIBUTING FACTOR. WE HAVE TROUBLE WITH SIMILAR RADIO CALL SIGNS ALL THE TIME.

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.