TSTM ACTIVITY INVOLVED WITH ENRTE WX/ B767 REQUESTS AND OBTAINS AMENDED CLRNC RTE ALT CHANGE BASED UPON AN ERRONEOUS ESTIMATE FOR THE NEXT POS.

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MAIQUETIA CTL. LOCATION: UL304 SBOUND AFTER CANAIMA (CMA) POS SBOUND ON UL304 AND APCHING ISANI POS WE REQUESTED AND RECEIVED A CLRNC TO DEVIATE 20 NM L OF CRS FOR WX. AFTER DEV WAS BEGUN WE WERE ASKED OUR ESTIMATE FOR ISANI. WE GAVE MQI AB40 FROM THE FMC FOR ISANI. BASED ON THIS ESTIMATE MQI GAVE US A CLRNC TO CLB TO FL370 FROM FL330. AFTER LEVEL OFF AND STILL DEVIATING IN HEADING SELECT; WE NOTICED THE ESTIMATED WE HAD GIVEN FOR ISANI WAS WRONG. ISANI WAS NOT THE ACTIVE WAYPOINT. WE CALCULATED A NEW ESTIMATE AB33. DISTANCE GS. WE ADVISED MQI OF NEW ESTIMATE AND THEY TOLD US TO MAKE A 360 DEG TURN TO THE L SO AS TO ARRIVE AT ISANI AT OUR ORIGINAL ESTIMATE. WHEN ABEAM ISANI; DEV WX; WE MADE 360 DEG TO L AND OUT OF TURN WENT DIRECT TO ISANI POS. OUR ESTIMATE FOR ISANI WAS NOW AB48. WE UPDATED OUR ESTIMATE WITH MQI AND THEY SAID OK. WE CROSSED ISANI AT AB48 AND PROCEEDED ROUTINE FOR BAL OF FLT. ISANI POS WAS GIVEN TO FLT SUPPORT LIMA ON HF. WE ALSO RPTED OUR 360 DEG TURN AND THE DELAY FROM SAME XING ISANI. DEV DISTR DID NOT HELP TO PICK UP FACT THAT RTE DATA ON SCREEN WAS INCORRECT WHILE I WAS IN HEADING SELECT. MQI WAS HARD TO REACH ON VHF AND SOME COM RELAYS WERE NECESSARY IN ALL THIS CLRNC REVISION.