Narrative:

In 2/89 I was working the north departure position at mia. As a trnee, I was monitored by a fully rated controller. My trainer and I became aware of WX beginning to build around the airport. We then turned off the mti portion of our radar to observe and WX cells within the area. We noticed large cells to the east, and to avoid them, began vectoring our east departures to the northeast. The WX conditions to the north and northwest appeared clear. An light transport aircraft departed runway 9L from mia and was radar idented. I then issued instructions to the pilot to climb to 7000'. Approximately 4 mi east of the airport I instructed the light transport to turn to a northbound heading of 340 degrees. I then radar idented an medium large transport also departing runway 9L from mia, and gave the pilot instructions to climb to 7000'. Both the light transport and medium large transport were routed out the same departure transition area. When the light transport was approximately 10 mi northeast of mia, I gave instructions to turn left heading 270 degrees (to intercept filed arwy) and to climb and maintain 12000' (the filed altitude). The medium large transport was now about 4 mi east of the airport, and I issued instruction to turn left on a 330 degree heading. Approximately 1 min later I noticed the light transport was turning wide, and the medium large transport appeared to be tracking a heading converging on the light transport. To achieve additional course divergence, I immediately issued instructions to the medium large transport to turn right heading 350 degrees. The pilot replied he could not accept the turn due to WX. The medium large transport at that time reflected an altitude of 6200', with the light transport at 6700'. My trainer then issued instructions to the medium large transport to descend to 6000' for traffic (the light transport) and gave the traffic location.at this point the medium large transport and light transport had about 3 mi sep and closing. The medium large transport pilot acknowledged the descent instructions, but reported he did not have the traffic in sight. About 10 seconds passed with the medium large transport now showing an altitude of 6800', with the light transport showing 7000'. There was now less than 3 mi of sep (breaking IFR sep requirements) and my trainer asked the medium large transport pilot to verify he was descending. The pilot replied he was descending and now had the traffic in sight. My trainer accordingly issued instructions to the pilot to maintain visibility sep. I believe this incident could have been avoided if the medium large transport pilot had requested a course deviation due to WX, or had issued a PIREP forewarning ATC of a problem in the area. Previous departures routed out the same area did not report any WX, nor request any course deviations due to same.

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Original NASA ASRS Text

Title: OVERTAKE ON DEP BETWEEN LTT AND MLG RESULTED IN LESS THAN STANDARD SEPARATION.

Narrative: IN 2/89 I WAS WORKING THE N DEP POS AT MIA. AS A TRNEE, I WAS MONITORED BY A FULLY RATED CTLR. MY TRAINER AND I BECAME AWARE OF WX BEGINNING TO BUILD AROUND THE ARPT. WE THEN TURNED OFF THE MTI PORTION OF OUR RADAR TO OBSERVE AND WX CELLS WITHIN THE AREA. WE NOTICED LARGE CELLS TO THE E, AND TO AVOID THEM, BEGAN VECTORING OUR E DEPS TO THE NE. THE WX CONDITIONS TO THE N AND NW APPEARED CLR. AN LTT ACFT DEPARTED RWY 9L FROM MIA AND WAS RADAR IDENTED. I THEN ISSUED INSTRUCTIONS TO THE PLT TO CLB TO 7000'. APPROX 4 MI E OF THE ARPT I INSTRUCTED THE LTT TO TURN TO A NBOUND HDG OF 340 DEGS. I THEN RADAR IDENTED AN MLG ALSO DEPARTING RWY 9L FROM MIA, AND GAVE THE PLT INSTRUCTIONS TO CLB TO 7000'. BOTH THE LTT AND MLG WERE ROUTED OUT THE SAME DEP TRANSITION AREA. WHEN THE LTT WAS APPROX 10 MI NE OF MIA, I GAVE INSTRUCTIONS TO TURN LEFT HDG 270 DEGS (TO INTERCEPT FILED ARWY) AND TO CLB AND MAINTAIN 12000' (THE FILED ALT). THE MLG WAS NOW ABOUT 4 MI E OF THE ARPT, AND I ISSUED INSTRUCTION TO TURN LEFT ON A 330 DEG HDG. APPROX 1 MIN LATER I NOTICED THE LTT WAS TURNING WIDE, AND THE MLG APPEARED TO BE TRACKING A HDG CONVERGING ON THE LTT. TO ACHIEVE ADDITIONAL COURSE DIVERGENCE, I IMMEDIATELY ISSUED INSTRUCTIONS TO THE MLG TO TURN RIGHT HDG 350 DEGS. THE PLT REPLIED HE COULD NOT ACCEPT THE TURN DUE TO WX. THE MLG AT THAT TIME REFLECTED AN ALT OF 6200', WITH THE LTT AT 6700'. MY TRAINER THEN ISSUED INSTRUCTIONS TO THE MLG TO DSND TO 6000' FOR TFC (THE LTT) AND GAVE THE TFC LOCATION.AT THIS POINT THE MLG AND LTT HAD ABOUT 3 MI SEP AND CLOSING. THE MLG PLT ACKNOWLEDGED THE DSCNT INSTRUCTIONS, BUT RPTED HE DID NOT HAVE THE TFC IN SIGHT. ABOUT 10 SECS PASSED WITH THE MLG NOW SHOWING AN ALT OF 6800', WITH THE LTT SHOWING 7000'. THERE WAS NOW LESS THAN 3 MI OF SEP (BREAKING IFR SEP REQUIREMENTS) AND MY TRAINER ASKED THE MLG PLT TO VERIFY HE WAS DSNDING. THE PLT REPLIED HE WAS DSNDING AND NOW HAD THE TFC IN SIGHT. MY TRAINER ACCORDINGLY ISSUED INSTRUCTIONS TO THE PLT TO MAINTAIN VIS SEP. I BELIEVE THIS INCIDENT COULD HAVE BEEN AVOIDED IF THE MLG PLT HAD REQUESTED A COURSE DEVIATION DUE TO WX, OR HAD ISSUED A PIREP FOREWARNING ATC OF A PROB IN THE AREA. PREVIOUS DEPS ROUTED OUT THE SAME AREA DID NOT RPT ANY WX, NOR REQUEST ANY COURSE DEVIATIONS DUE TO SAME.

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.