Narrative:

Conducting OJT on radar trainee and let trainee go too far. When I attempted to stop aircraft to maintain 1000 ft separation I used wrong call sign as they were similar. Same company air carrier xa air carrier xb all on frequency. Changing call sign numbers might have prevented confusion. Air carrier xa heading eastbound at FL230 wants lower. Aircraft Y at 10 O'clock and 15 mi sebound descending to 150 descending out of 220 is traffic. Air carrier xb given a 190 vector and descended to 110. Turn was not going to be sufficient. I was waiting for trainee to fix problem. I was going to stop air carrier xa's descent to maintain 1000 ft separation but I said air carrier xb instead. Aircraft Y turned to a 110 heading and told to report altitude leaving but only said 20700 and air carrier xa was at 21500. Bad judgement involved on my part in letting trainee go too far. Also when immediate action was to be taken I called same company flight by wrong number using air carrier xb. Supplemental information from acn 197822: spacing was being issued for sdf arrs through the gate. Same company air carrier's were the first 2 followed by aircraft Y and air carrier xa. Air carrier xb was given a clearance to maintain 180 to keep him from descending into air carrier xb. Meanwhile aircraft Y was given a clearance to descend from 220 to 150 and changed from a 190 heading to a 170 heading. Air carrier xa then asked for lower and was given a 190 heading to descend to 110. Air carrier xa made a sharp turn to 190 heading and an increased descent rate which was greater than aircraft Y. When the instructor jumped in to stop air carrier xa's descent he mistakenly used air carrier xb's call sign. Air carrier xb responded he was level at 180. The trainer then restated for air carrier xa to stop his descent and say altitude leaving. At this time separation had been lost.

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Original NASA ASRS Text

Title: ACR XA HAD LTSS FROM ACFT Y. SYS ERROR.

Narrative: CONDUCTING OJT ON RADAR TRAINEE AND LET TRAINEE GO TOO FAR. WHEN I ATTEMPTED TO STOP ACFT TO MAINTAIN 1000 FT SEPARATION I USED WRONG CALL SIGN AS THEY WERE SIMILAR. SAME COMPANY ACR XA ACR XB ALL ON FREQ. CHANGING CALL SIGN NUMBERS MIGHT HAVE PREVENTED CONFUSION. ACR XA HDG EBOUND AT FL230 WANTS LOWER. ACFT Y AT 10 O'CLOCK AND 15 MI SEBOUND DSNDING TO 150 DSNDING OUT OF 220 IS TFC. ACR XB GIVEN A 190 VECTOR AND DSNDED TO 110. TURN WAS NOT GOING TO BE SUFFICIENT. I WAS WAITING FOR TRAINEE TO FIX PROBLEM. I WAS GOING TO STOP ACR XA'S DSCNT TO MAINTAIN 1000 FT SEPARATION BUT I SAID ACR XB INSTEAD. ACFT Y TURNED TO A 110 HDG AND TOLD TO RPT ALT LEAVING BUT ONLY SAID 20700 AND ACR XA WAS AT 21500. BAD JUDGEMENT INVOLVED ON MY PART IN LETTING TRAINEE GO TOO FAR. ALSO WHEN IMMEDIATE ACTION WAS TO BE TAKEN I CALLED SAME COMPANY FLT BY WRONG NUMBER USING ACR XB. SUPPLEMENTAL INFO FROM ACN 197822: SPACING WAS BEING ISSUED FOR SDF ARRS THROUGH THE GATE. SAME COMPANY ACR'S WERE THE FIRST 2 FOLLOWED BY ACFT Y AND ACR XA. ACR XB WAS GIVEN A CLRNC TO MAINTAIN 180 TO KEEP HIM FROM DSNDING INTO ACR XB. MEANWHILE ACFT Y WAS GIVEN A CLRNC TO DSND FROM 220 TO 150 AND CHANGED FROM A 190 HDG TO A 170 HDG. ACR XA THEN ASKED FOR LOWER AND WAS GIVEN A 190 HDG TO DSND TO 110. ACR XA MADE A SHARP TURN TO 190 HDG AND AN INCREASED DSCNT RATE WHICH WAS GREATER THAN ACFT Y. WHEN THE INSTRUCTOR JUMPED IN TO STOP ACR XA'S DSCNT HE MISTAKENLY USED ACR XB'S CALL SIGN. ACR XB RESPONDED HE WAS LEVEL AT 180. THE TRAINER THEN RESTATED FOR ACR XA TO STOP HIS DSCNT AND SAY ALT LEAVING. AT THIS TIME SEPARATION HAD BEEN LOST.

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.