Narrative:

Medium large transport X was southbound to lax via ave-F/M expecting runway 24/25 profile descent. Medium large transport Y was eastbound santa barbara to psp via fillmore. Direct palmdale at 17000', I cleared medium large transport X to cross 5 mi south of fillmore at FL180, then cleared for runway 24/25 profile descent. The pilot read back this clearance. When medium large transport X was 5 mi north of fillmore and 5 mi from medium large transport Y, I issued traffic as 3 O'clock, 5 mi, eastbound at 17000'. The pilot replied that the traffic was in sight. Immediately after that I observed the data block on medium large transport X to show 17800'. I told the pilot to climb to FL180 as cleared. He replied that he was cleared to cross 5 mi north of fillmore at FL180 and had read that back. When we reviewed the tape, it was clear that he had read back 5 south. To prevent a recurrence of this, I suggest we eliminate the profile descent and put in a STAR. With a STAR, I would not have issued the crossing restriction, but would have waited till the aircraft were 5 mi apart, then issued a lower altitude.

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Original NASA ASRS Text

Title: ACFT GIVEN CROSSING RESTRICTION FOR SEPARATION FROM CROSSING TRAFFIC AND STARTED DESCENT TOO SOON CREATING LESS THAN STANDARD SEPARATION.

Narrative: MLG X WAS SBND TO LAX VIA AVE-F/M EXPECTING RWY 24/25 PROFILE DSCNT. MLG Y WAS EBND SANTA BARBARA TO PSP VIA FILLMORE. DIRECT PALMDALE AT 17000', I CLRED MLG X TO CROSS 5 MI S OF FILLMORE AT FL180, THEN CLRED FOR RWY 24/25 PROFILE DSCNT. THE PLT READ BACK THIS CLRNC. WHEN MLG X WAS 5 MI N OF FILLMORE AND 5 MI FROM MLG Y, I ISSUED TFC AS 3 O'CLOCK, 5 MI, EBND AT 17000'. THE PLT REPLIED THAT THE TFC WAS IN SIGHT. IMMEDIATELY AFTER THAT I OBSERVED THE DATA BLOCK ON MLG X TO SHOW 17800'. I TOLD THE PLT TO CLB TO FL180 AS CLRED. HE REPLIED THAT HE WAS CLRED TO CROSS 5 MI N OF FILLMORE AT FL180 AND HAD READ THAT BACK. WHEN WE REVIEWED THE TAPE, IT WAS CLEAR THAT HE HAD READ BACK 5 S. TO PREVENT A RECURRENCE OF THIS, I SUGGEST WE ELIMINATE THE PROFILE DSCNT AND PUT IN A STAR. WITH A STAR, I WOULD NOT HAVE ISSUED THE XING RESTRICTION, BUT WOULD HAVE WAITED TILL THE ACFT WERE 5 MI APART, THEN ISSUED A LOWER ALT.

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.