Narrative:

I was working the feeder final position at mia TRACON. Aircraft X was on left downwind for runway 9L. Aircraft Y was established on the runway 9R localizer. Aircraft Y was at 3000 ft. Aircraft X was heading 260 degrees when I turned him to heading 180 degrees. He appeared to be turning unusually slowly to the 180 degree heading, so I then issued the heading 160 degrees and then 120 degrees to join the runway 9L localizer. During those turns, I questioned aircraft X on his rate of turn and whether he was even turning at one point. Aircraft X apparently had held the 180 degree heading for 12-16 seconds even though he was issued the 160 degree and the 120 degree heading before he ever reached his 180 degree heading. I exchanged traffic between both aircraft. I asked aircraft Y if he could maintain visual separation with the aircraft X taking the wide turn to the parallel final. Aircraft Y said he would maintain visual separation. I had descended aircraft X to 1500 ft on the downwind. Their closest proximity was about 2 mi and 800 ft. I cleared both aircraft for ILS approachs then switched them to the tower. I believe the loss of standard separation occurred because the pilot of aircraft X failed to comply with an ATC instruction in a timely manner.

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Original NASA ASRS Text

Title: MIA APCH CTLR LOSES STANDARD SEPARATION WHEN VECTORING 2 ACR JETS TO THE MIA RWYS 9 FINAL APCH COURSE.

Narrative: I WAS WORKING THE FEEDER FINAL POS AT MIA TRACON. ACFT X WAS ON L DOWNWIND FOR RWY 9L. ACFT Y WAS ESTABLISHED ON THE RWY 9R LOC. ACFT Y WAS AT 3000 FT. ACFT X WAS HDG 260 DEGS WHEN I TURNED HIM TO HDG 180 DEGS. HE APPEARED TO BE TURNING UNUSUALLY SLOWLY TO THE 180 DEG HDG, SO I THEN ISSUED THE HDG 160 DEGS AND THEN 120 DEGS TO JOIN THE RWY 9L LOC. DURING THOSE TURNS, I QUESTIONED ACFT X ON HIS RATE OF TURN AND WHETHER HE WAS EVEN TURNING AT ONE POINT. ACFT X APPARENTLY HAD HELD THE 180 DEG HDG FOR 12-16 SECONDS EVEN THOUGH HE WAS ISSUED THE 160 DEG AND THE 120 DEG HDG BEFORE HE EVER REACHED HIS 180 DEG HDG. I EXCHANGED TFC BTWN BOTH ACFT. I ASKED ACFT Y IF HE COULD MAINTAIN VISUAL SEPARATION WITH THE ACFT X TAKING THE WIDE TURN TO THE PARALLEL FINAL. ACFT Y SAID HE WOULD MAINTAIN VISUAL SEPARATION. I HAD DSNDED ACFT X TO 1500 FT ON THE DOWNWIND. THEIR CLOSEST PROX WAS ABOUT 2 MI AND 800 FT. I CLRED BOTH ACFT FOR ILS APCHS THEN SWITCHED THEM TO THE TWR. I BELIEVE THE LOSS OF STANDARD SEPARATION OCCURRED BECAUSE THE PLT OF ACFT X FAILED TO COMPLY WITH AN ATC INSTRUCTION IN A TIMELY MANNER.

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.