Narrative:

Air carrier X (ATR42) at FL200 was en route from houston to brownsville about 60 mi northeast of crp. Air carrier Y (B737) was at FL260 from houston to crp. I could easily see that air carrier Y would overtake the air carrier X about the time air carrier Y would want to descend for landing. I called the previous radar sector requesting control for descent air carrier Y. My intention was to force air carrier Y under air carrier X earlier to facilitate arrival descent. By the time air carrier Y came to my frequency, that plan would no longer work. I decided just to hold air carrier Y high over the traffic at FL210 until he outran him and then let him down. As required, I issued traffic information to both aircraft. They reported each other in sight. Then I had to catch up on some other required, but lower priority duties that had stacked up. When I returned to the radar scope air carrier Y was about 3 mi in front of air carrier X. I asked air carrier X if he still had the B737 in sight and if he could maintain visual separation from him. When air carrier X responded 'I have him in sight and couldn't catch him if I tried,' I instructed him to maintain visual separation and issued descent clearance to air carrier Y. The visual separation standard I employed was misapplied due to the altitudes involved. The standard is FL180 and below. I had been aware of confusion in the standard within the FAA and had read a briefing clarifying the standard, but I also had read of facilities testing and using FL230 as the standard. In my haste to provide air carrier Y a comfortable descent and having both pilots report seeing each other, my own confusion led me to use an inappropriate standard. Minimum separation was 3.5 mi and 500 ft vertically. While this cannot excuse my error, I do feel that the seemingly continuous changes in standards have a tremendous impact in those decisions made instantaneously from memory. In my 23 yrs as a controller, some standards have fluxed back and forth, some have changed almost yrly, and few have remained static. These changes put very much information into the brain, but no one has trained us how to purge the bad information.

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Original NASA ASRS Text

Title: ARTCC RADAR CTLR USED VISUAL SEPARATION TO DSND A B737 THROUGH THE ALT OF AN ATR42 WHILE ACFT WERE IN PCA. AFTER CONFLICT ALERT CAUGHT THE LTSS, THE CTLR REMEMBERED VISUAL SEPARATION CAN ONLY BE USED BELOW FL180.

Narrative: ACR X (ATR42) AT FL200 WAS ENRTE FROM HOUSTON TO BROWNSVILLE ABOUT 60 MI NE OF CRP. ACR Y (B737) WAS AT FL260 FROM HOUSTON TO CRP. I COULD EASILY SEE THAT ACR Y WOULD OVERTAKE THE ACR X ABOUT THE TIME ACR Y WOULD WANT TO DSND FOR LNDG. I CALLED THE PREVIOUS RADAR SECTOR REQUESTING CTL FOR DSCNT ACR Y. MY INTENTION WAS TO FORCE ACR Y UNDER ACR X EARLIER TO FACILITATE ARR DSCNT. BY THE TIME ACR Y CAME TO MY FREQ, THAT PLAN WOULD NO LONGER WORK. I DECIDED JUST TO HOLD ACR Y HIGH OVER THE TFC AT FL210 UNTIL HE OUTRAN HIM AND THEN LET HIM DOWN. AS REQUIRED, I ISSUED TFC INFO TO BOTH ACFT. THEY RPTED EACH OTHER IN SIGHT. THEN I HAD TO CATCH UP ON SOME OTHER REQUIRED, BUT LOWER PRIORITY DUTIES THAT HAD STACKED UP. WHEN I RETURNED TO THE RADAR SCOPE ACR Y WAS ABOUT 3 MI IN FRONT OF ACR X. I ASKED ACR X IF HE STILL HAD THE B737 IN SIGHT AND IF HE COULD MAINTAIN VISUAL SEPARATION FROM HIM. WHEN ACR X RESPONDED 'I HAVE HIM IN SIGHT AND COULDN'T CATCH HIM IF I TRIED,' I INSTRUCTED HIM TO MAINTAIN VISUAL SEPARATION AND ISSUED DSCNT CLRNC TO ACR Y. THE VISUAL SEPARATION STANDARD I EMPLOYED WAS MISAPPLIED DUE TO THE ALTS INVOLVED. THE STANDARD IS FL180 AND BELOW. I HAD BEEN AWARE OF CONFUSION IN THE STANDARD WITHIN THE FAA AND HAD READ A BRIEFING CLARIFYING THE STANDARD, BUT I ALSO HAD READ OF FACILITIES TESTING AND USING FL230 AS THE STANDARD. IN MY HASTE TO PROVIDE ACR Y A COMFORTABLE DSCNT AND HAVING BOTH PLTS RPT SEEING EACH OTHER, MY OWN CONFUSION LED ME TO USE AN INAPPROPRIATE STANDARD. MINIMUM SEPARATION WAS 3.5 MI AND 500 FT VERTLY. WHILE THIS CANNOT EXCUSE MY ERROR, I DO FEEL THAT THE SEEMINGLY CONTINUOUS CHANGES IN STANDARDS HAVE A TREMENDOUS IMPACT IN THOSE DECISIONS MADE INSTANTANEOUSLY FROM MEMORY. IN MY 23 YRS AS A CTLR, SOME STANDARDS HAVE FLUXED BACK AND FORTH, SOME HAVE CHANGED ALMOST YRLY, AND FEW HAVE REMAINED STATIC. THESE CHANGES PUT VERY MUCH INFO INTO THE BRAIN, BUT NO ONE HAS TRAINED US HOW TO PURGE THE BAD INFO.

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.