Narrative:

Air carrier abc X and air carrier abd both were on ZID's frequency 134.67 (high side). Controller transferred air carrier abd to 121.32. Air carrier abc X took the frequency change. Air carrier abc X called on 121.32. Low side controller (121.32) accepted and automated handoff on air carrier abd. Low side controller cleared air carrier abd to FL190. Air carrier abc X read back the clearance. Air carrier abc X descended to FL190 from FL350. An air carrier Y was within 5 mi of the air carrier abc X when air carrier abc X left FL350. Both vertical and lateral separation was lost. In summary, twice air carrier abc X took air carrier abd clearance. Supplemental information from acn 261727: at cruise of FL350, we received a frequency change to ZID (122.22). I checked in with ZID on the frequency. ZID gave us a clearance to descend from FL350 to FL190. We started a slow descent due to being about 140 NM from day. Immediately, someone came on frequency and requested we return to previous frequency. After checking in with center, I advised them of our descent clearance. Center advised that we should return to FL350. At this time, we reversed descent at around FL340 to climb to FL350. We received a TA alert on traffic at FL330. No evasive action required, no RA alert received. Controller apologized and handed us off to another ZID frequency who asked us to call upon landing. We called and left a message on the recorder. We believe center gave incorrect call sign to us in the frequency transfer. ZID may have believed we were another aircraft in clearing us to descend.

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Original NASA ASRS Text

Title: ACR MLG TOOK COMPANY ACFT DSCNT CLRNC AND HAD LTSS WITH AN OPPOSITE DIRECTION ACR ACFT THAT WAS BELOW HIM. CONFLICT ALERT AND TCASII ACTIVATED.

Narrative: ACR ABC X AND ACR ABD BOTH WERE ON ZID'S FREQ 134.67 (HIGH SIDE). CTLR TRANSFERRED ACR ABD TO 121.32. ACR ABC X TOOK THE FREQ CHANGE. ACR ABC X CALLED ON 121.32. LOW SIDE CTLR (121.32) ACCEPTED AND AUTOMATED HDOF ON ACR ABD. LOW SIDE CTLR CLRED ACR ABD TO FL190. ACR ABC X READ BACK THE CLRNC. ACR ABC X DSNDED TO FL190 FROM FL350. AN ACR Y WAS WITHIN 5 MI OF THE ACR ABC X WHEN ACR ABC X LEFT FL350. BOTH VERT AND LATERAL SEPARATION WAS LOST. IN SUMMARY, TWICE ACR ABC X TOOK ACR ABD CLRNC. SUPPLEMENTAL INFO FROM ACN 261727: AT CRUISE OF FL350, WE RECEIVED A FREQ CHANGE TO ZID (122.22). I CHKED IN WITH ZID ON THE FREQ. ZID GAVE US A CLRNC TO DSND FROM FL350 TO FL190. WE STARTED A SLOW DSCNT DUE TO BEING ABOUT 140 NM FROM DAY. IMMEDIATELY, SOMEONE CAME ON FREQ AND REQUESTED WE RETURN TO PREVIOUS FREQ. AFTER CHKING IN WITH CTR, I ADVISED THEM OF OUR DSCNT CLRNC. CTR ADVISED THAT WE SHOULD RETURN TO FL350. AT THIS TIME, WE REVERSED DSCNT AT AROUND FL340 TO CLB TO FL350. WE RECEIVED A TA ALERT ON TFC AT FL330. NO EVASIVE ACTION REQUIRED, NO RA ALERT RECEIVED. CTLR APOLOGIZED AND HANDED US OFF TO ANOTHER ZID FREQ WHO ASKED US TO CALL UPON LNDG. WE CALLED AND LEFT A MESSAGE ON THE RECORDER. WE BELIEVE CTR GAVE INCORRECT CALL SIGN TO US IN THE FREQ TRANSFER. ZID MAY HAVE BELIEVED WE WERE ANOTHER ACFT IN CLRING US TO DSND.

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.