Narrative:

At approximately XX30 air carrier checked in the frequency at 10000' 20 mi east of sju after accepting the handoff from center. I issued a heading of 270 degree and advised him he could expect the lagoon visibility runway 8 approach. At approximately XX40, small transport VFR at 16500' checked in the frequency 25 mi east of sju after accepting the handoff from the center. I instructed small transport to enter right traffic for runway 10. I realized that small transport was high (16500') and fast (450 KTS). I gave small transport a heading of 260 degrees to keep him outside of air carrier. At about XX50 I saw that small transport had a normal rate of descent, altitude was showing 13700'. I gave air carrier a descent clearance from 8000 to 6000' and a heading of 280 degrees. A minute later, at approximately XX51, I saw that both aircraft were in close proximity and that the altitude on small transport had drastically changed. I asked small transport to say his altitude. He reported 7500'. I immediately issued the traffic and small transport reported air carrier in sight. I then instructed small transport to maintain visibility sep from air carrier. Right after I issued traffic to air carrier off his right side and 2 mi, air carrier responded by saying: 'that's an awfully close 2 mi,' I reported the incident to the supervisor. I never issued an 'at or above' altitude restriction to small transport. Since he was 6000' above air carrier and about 5 mi in back and overtaking. I believed the situation occurred because small transport VFR descended way beyond normal rate of descent (6000 FPM) after descending at normal rate. I will now issue an altitude restriction since you never know what to expect from pilots. I also suggest that there be an far specifying that the pilot of an IFR as well as a VFR advise the controller if he/she will descend or climb in an abnormal rate.

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Original NASA ASRS Text

Title: CTLR DESCENDED SMT IN CLOSE PROX TO WDB WITHOUT ISSUING TRAFFIC ADVISORIES UNTIL TOO LATE.

Narrative: AT APPROX XX30 ACR CHKED IN THE FREQ AT 10000' 20 MI E OF SJU AFTER ACCEPTING THE HDOF FROM CENTER. I ISSUED A HDG OF 270 DEG AND ADVISED HIM HE COULD EXPECT THE LAGOON VIS RWY 8 APCH. AT APPROX XX40, SMT VFR AT 16500' CHKED IN THE FREQ 25 MI E OF SJU AFTER ACCEPTING THE HDOF FROM THE CENTER. I INSTRUCTED SMT TO ENTER RIGHT TFC FOR RWY 10. I REALIZED THAT SMT WAS HIGH (16500') AND FAST (450 KTS). I GAVE SMT A HDG OF 260 DEGS TO KEEP HIM OUTSIDE OF ACR. AT ABOUT XX50 I SAW THAT SMT HAD A NORMAL RATE OF DSCNT, ALT WAS SHOWING 13700'. I GAVE ACR A DSCNT CLRNC FROM 8000 TO 6000' AND A HDG OF 280 DEGS. A MINUTE LATER, AT APPROX XX51, I SAW THAT BOTH ACFT WERE IN CLOSE PROX AND THAT THE ALT ON SMT HAD DRASTICALLY CHANGED. I ASKED SMT TO SAY HIS ALT. HE RPTED 7500'. I IMMEDIATELY ISSUED THE TFC AND SMT RPTED ACR IN SIGHT. I THEN INSTRUCTED SMT TO MAINTAIN VIS SEP FROM ACR. RIGHT AFTER I ISSUED TFC TO ACR OFF HIS RIGHT SIDE AND 2 MI, ACR RESPONDED BY SAYING: 'THAT'S AN AWFULLY CLOSE 2 MI,' I RPTED THE INCIDENT TO THE SUPVR. I NEVER ISSUED AN 'AT OR ABOVE' ALT RESTRICTION TO SMT. SINCE HE WAS 6000' ABOVE ACR AND ABOUT 5 MI IN BACK AND OVERTAKING. I BELIEVED THE SITUATION OCCURRED BECAUSE SMT VFR DSNDED WAY BEYOND NORMAL RATE OF DSCNT (6000 FPM) AFTER DSNDING AT NORMAL RATE. I WILL NOW ISSUE AN ALT RESTRICTION SINCE YOU NEVER KNOW WHAT TO EXPECT FROM PLTS. I ALSO SUGGEST THAT THERE BE AN FAR SPECIFYING THAT THE PLT OF AN IFR AS WELL AS A VFR ADVISE THE CTLR IF HE/SHE WILL DSND OR CLB IN AN ABNORMAL RATE.

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.