FOREIGN ARTCC COORDINATED NEW ALT FOR ACR ACFT; WHICH WAS APPROVED BY CTLR AT ZHU. LATER THE ACR ACFT HAD LTSS WITH A CORP ACFT OVER A NON RADAR FIX. ACR ACFT SAW THE POTENTIAL CONFLICT ON ITS TCASII; BUT NOT BEFORE SEPARATION WAS LOST AND ACFT SAW EACH OTHER.

Narrative

WE WERE WORKING THE SECTOR OVER THE GULF OF MEXICO (NON RADAR). MERIDA CTR PASSED A FLT PLAN TO OUR SECTOR AT FL310. SHORTLY THEREAFTER; MERIDA CTR CALLED BACK TO REVISE THE ACFT'S ALT TO FL350. THE CTLR WORKING THE D- SIDE APPROVED THE ALT CHANGE; BUT DID NOT FOLLOW THROUGH WITH MARKING THE OTHER STRIPS ON THE ACFT (NWBOUND). WE HAD A SWBOUND ACFT AT FL350 WHICH WAS XING WITH THE NWBOUND ACFT AT FL350; WHICH WE WERE SHOWING AN ALT OF FL310 WHERE THEY CROSSED. WE DIDN'T KNOW OF A PROB UNTIL THE NWBOUND ACFT RPTED AN ACFT ON HIS TCASII AT HIS 3 O'CLOCK. THE NWBOUND ACFT WAS ADVISED THAT THE SWBOUND ACFT WAS A CITATION AT FL350. THE PLT RESPONDED; FL350? HE WAS TOLD AFFIRMATIVE AND ASKED HIS ASSIGNED ALT. HE REPLIED FL350; WHICH WE WERE SHOWING FL310. I COULD NOT CLB OR DSND EITHER ACFT BECAUSE OF TFC AT FL330 AND FL370 IN THE VICINITY (ALL NON RADAR). THE SWBOUND ACFT WAS ADVISED OF THE TFC AND RESPONDED; 'TFC IN SIGHT.' THE NWBOUND ACFT RPTED THAT HE HAD AN ALT RESOLUTION ALERT FROM HIS TCASII. SUPPLEMENTAL INFO FROM ACN 265214: A B727 AND C550 CROSSED AT FL350 NON RADAR WITH LESS THAN 15 MINS ICAO SEPARATION. THE B727 WAS ORIGINALLY AT FL310. MERIDA CTR PASSED THE REVISED ALT OF FL350 AND THE FIRST D-SIDE APPROVED IT. #1 D-SIDE WROTE FL350 ON THE FIRST STRIP BUT NOT ON THE SECOND OR THIRD. THAT CTLR ALSO NEGLECTED TO ENTER THE ALT IN THE COMPUTER. THE SECOND D-SIDE RELIEVED THE FIRST D-SIDE AND DID NOT SEE THE STRIP MARKING ERRORS. THE SECOND D-SIDE THEN RELIEVED THE R-SIDE AND COMBINED BOTH POS TO THE R-SIDE. 30 MINS LATER; THE SECOND R-SIDE WAS RELIEVED. RIGHT AFTER BRIEFING THE B727 CHKED ON AT FL350. THIS WAS ROGERED BUT NOT CAUGHT BY R-SIDE #3. 8 MINS LATER THE B727 ASKED WHO WAS HIS TFC AT FL350 AND 3 O'CLOCK. BEFORE THE B727 ENTERED ZHU AIRSPACE A DEP OFF OF NEW WAS CLBED TO FL350 BECAUSE HIS REQUESTED ALT OF FL310 WAS ALREADY TAKEN BY THE B727 AS REFLECTED BY THE B727'S SECOND STRIP. THE SECOND D-SIDE APPROVED FL350 ON THE C550 AFTER ASSUMING THE R-SIDE POS. IF THE B727 HAD RPTED THE FIR IN ACCORDANCE WITH FARS AND ICAO RULES; THIS ERROR WOULD HAVE BEEN CAUGHT AND RESOLVED BEFORE LOSS OF SEPARATION OCCURRED.