Narrative:

I was one-manning the somerset super high sector at indianapolis ARTCC. I was working both the radar and manual position due to staffing limitations. I had 10 airplanes on the frequency. By the way, my airspace was FL350 and above, one of the airplanes was deviating around weather, and 4 other aircraft were on vectors, one of the vectored aircraft was large transport X (abc) the other 3 aircraft being vectored were in the northern region of my airspace. I was taking a northbound air carrier flight at FL350 between two wbound air carrier flts at FL350. It was a routine maneuver, but I didn't have much room for error. The two wbound flts were only 15 miles in trail. Medium large transport Y (abc) called on at FL350. I did not notice the similar call sign with large transport X (abc), and neither flight was informed on the similar call signs. I needed to descend large transport X (abc) to avoid my aircraft deviating around the WX. The controller below me approved descent to fl 240. I cleared large transport X (abc) to FL240. Medium large transport Y (abc) acknowledged the clearance. I missed the readback. 20 seconds later large transport X (abc) requested lower. I questioningly (I don't think that's a word) re-cleared large transport X (abc) to FL240. My 'field goal' still had my attention. When conflict alert activated between medium large transport X (abc) and large transport Z, sbound at FL330. Medium large transport Y (abc) was out of FL344, and got down to FL337, before I told him to climb to FL350, that he had taken another aircraft's clearance. I turned him due west and called his traffic, asked him to report level at FL350. He reported the traffic in sight and level at 350, 9 seconds after oed activated. The closest they got was 2.6 miles and 1500'. Supplemental information from acn 86709: a short time later the controller told us that conflict bell had gone off and we could call quality assurance on the ground. Which I did. After reviewing the tapes it was concluded that the controller had cleared large transport X (abc) - to FL240 but didn't catch the fact that we responded to the call. Large transport X (abc) didn't respond to the initial call but asked for a lower at that same time, that's when the controller seeing us descending realized his error. The quality assurance people were very responsive to the problem they filed a controller operational error for failure to advise of like call signs, and not catching the wrong read back. According to quality assurance a pilot deviation was not filed.

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Original NASA ASRS Text

Title: MLG COPIED CLRNC TO DESCEND MEANT FOR LGT WITH SAME A/N AND HAD LESS THAN STANDARD SEPARATION WITH ANOTHER LGT OPPOSITE DIRECTION. CTLR MISSED INCORRECT READBACK AND HAD NOT ADVISED LGT AND MLG OF SAME A/N SITUATION.

Narrative: I WAS ONE-MANNING THE SOMERSET SUPER HIGH SECTOR AT INDIANAPOLIS ARTCC. I WAS WORKING BOTH THE RADAR AND MANUAL POSITION DUE TO STAFFING LIMITATIONS. I HAD 10 AIRPLANES ON THE FREQ. BY THE WAY, MY AIRSPACE WAS FL350 AND ABOVE, ONE OF THE AIRPLANES WAS DEVIATING AROUND WEATHER, AND 4 OTHER ACFT WERE ON VECTORS, ONE OF THE VECTORED ACFT WAS LGT X (ABC) THE OTHER 3 ACFT BEING VECTORED WERE IN THE NORTHERN REGION OF MY AIRSPACE. I WAS TAKING A NBOUND ACR FLT AT FL350 BETWEEN TWO WBOUND ACR FLTS AT FL350. IT WAS A ROUTINE MANEUVER, BUT I DIDN'T HAVE MUCH ROOM FOR ERROR. THE TWO WBOUND FLTS WERE ONLY 15 MILES IN TRAIL. MLG Y (ABC) CALLED ON AT FL350. I DID NOT NOTICE THE SIMILAR CALL SIGN WITH LGT X (ABC), AND NEITHER FLT WAS INFORMED ON THE SIMILAR CALL SIGNS. I NEEDED TO DESCEND LGT X (ABC) TO AVOID MY ACFT DEVIATING AROUND THE WX. THE CTLR BELOW ME APPROVED DESCENT TO FL 240. I CLRED LGT X (ABC) TO FL240. MLG Y (ABC) ACKNOWLEDGED THE CLRNC. I MISSED THE READBACK. 20 SECONDS LATER LGT X (ABC) REQUESTED LOWER. I QUESTIONINGLY (I DON'T THINK THAT'S A WORD) RE-CLRED LGT X (ABC) TO FL240. MY 'FIELD GOAL' STILL HAD MY ATTN. WHEN CONFLICT ALERT ACTIVATED BETWEEN MLG X (ABC) AND LGT Z, SBOUND AT FL330. MLG Y (ABC) WAS OUT OF FL344, AND GOT DOWN TO FL337, BEFORE I TOLD HIM TO CLIMB TO FL350, THAT HE HAD TAKEN ANOTHER ACFT'S CLRNC. I TURNED HIM DUE WEST AND CALLED HIS TFC, ASKED HIM TO REPORT LEVEL AT FL350. HE REPORTED THE TFC IN SIGHT AND LEVEL AT 350, 9 SECONDS AFTER OED ACTIVATED. THE CLOSEST THEY GOT WAS 2.6 MILES AND 1500'. SUPPLEMENTAL INFORMATION FROM ACN 86709: A SHORT TIME LATER THE CTLR TOLD US THAT CONFLICT BELL HAD GONE OFF AND WE COULD CALL QUALITY ASSURANCE ON THE GND. WHICH I DID. AFTER REVIEWING THE TAPES IT WAS CONCLUDED THAT THE CTLR HAD CLRED LGT X (ABC) - TO FL240 BUT DIDN'T CATCH THE FACT THAT WE RESPONDED TO THE CALL. LGT X (ABC) DIDN'T RESPOND TO THE INITIAL CALL BUT ASKED FOR A LOWER AT THAT SAME TIME, THAT'S WHEN THE CTLR SEEING US DESCENDING REALIZED HIS ERROR. THE QUALITY ASSURANCE PEOPLE WERE VERY RESPONSIVE TO THE PROBLEM THEY FILED A CTLR OPERATIONAL ERROR FOR FAILURE TO ADVISE OF LIKE CALL SIGNS, AND NOT CATCHING THE WRONG READ BACK. ACCORDING TO QUALITY ASSURANCE A PLT DEVIATION WAS NOT FILED.

Data retrieved from NASA's ASRS site as of August 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.