Narrative:

I was vectoring aircraft for the ILS runway 10. WX was MVFR, prevailing visibility 4 mi with 2 mi on final. The first aircraft was small aircraft X, and the following aircraft was widebody transport air carrier Y. Small aircraft X was cleared for the ILS 3 mi from the FAF, airspeed 140 KTS, and was instructed to maintain his present speed until the marker. Air carrier Y was cleared for the ILS, 10 mi from the FAF. Small aircraft X called shortly after and reported over the marker. I switched X to tower frequency. I saw that I had enough sep between X and Y (approximately 6 mi). I instructed air carrier Y to maintain his present speed (180 KTS) to the marker and to contact tower. About a minute later, the tower called me and said, 'I have less that 3 mi between X and Y, what do you want me to do?'. Air carrier Y was issued 180 degree heading and 3000' and was vectored for another ILS. After reviewing the data extractions, we realized that small aircraft X did not comply with the speed instructions. Small aircraft X had reduced to 90 KTS prior to the marker and then held 75 KTS inside the marker on final. I failed to detect the speed on small aircraft X which resulted in my system error.

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Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION WHEN WDB-ACR OVERTOOK SMA ON ILS FINAL. OPERATIONAL ERROR.

Narrative: I WAS VECTORING ACFT FOR THE ILS RWY 10. WX WAS MVFR, PREVAILING VIS 4 MI WITH 2 MI ON FINAL. THE FIRST ACFT WAS SMA X, AND THE FOLLOWING ACFT WAS WDB ACR Y. SMA X WAS CLRED FOR THE ILS 3 MI FROM THE FAF, AIRSPEED 140 KTS, AND WAS INSTRUCTED TO MAINTAIN HIS PRESENT SPD UNTIL THE MARKER. ACR Y WAS CLRED FOR THE ILS, 10 MI FROM THE FAF. SMA X CALLED SHORTLY AFTER AND RPTED OVER THE MARKER. I SWITCHED X TO TWR FREQ. I SAW THAT I HAD ENOUGH SEP BTWN X AND Y (APPROX 6 MI). I INSTRUCTED ACR Y TO MAINTAIN HIS PRESENT SPD (180 KTS) TO THE MARKER AND TO CONTACT TWR. ABOUT A MINUTE LATER, THE TWR CALLED ME AND SAID, 'I HAVE LESS THAT 3 MI BTWN X AND Y, WHAT DO YOU WANT ME TO DO?'. ACR Y WAS ISSUED 180 DEG HDG AND 3000' AND WAS VECTORED FOR ANOTHER ILS. AFTER REVIEWING THE DATA EXTRACTIONS, WE REALIZED THAT SMA X DID NOT COMPLY WITH THE SPD INSTRUCTIONS. SMA X HAD REDUCED TO 90 KTS PRIOR TO THE MARKER AND THEN HELD 75 KTS INSIDE THE MARKER ON FINAL. I FAILED TO DETECT THE SPD ON SMA X WHICH RESULTED IN MY SYS ERROR.

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.