Narrative:

Sbound approaching intersection in oceanic airspace. We had already been approved for a 20 NM right deviation (west). We subsequently requested through cpdlc a further deviation up to 40 NM right for WX avoidance. Our request to deviate was initially denied. At the time; we observed only 1 aircraft on the TCAS; 1000 ft above our altitude and 20 NM left (east). Using cpdlc inputs we declared an emergency and using captain's emergency authority/authorized began to deviate up to 40 NM right (west) around convective WX at our altitude that extended 35 NM west of track and 40 NM east. There were no additional aircraft on our TCAS screen. ZZZ quickly responded with clearance to deviate up to 40 NM right of track and asked that we report back on course. We complied with the amended clearance; canceled the emergency; and reported back on course. The flight continued to destination without further development.

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Original NASA ASRS Text

Title: B777 FLT CREW NEEDS TO DECLARE EMER TO DEVIATE AROUND WX IN OCEANIC AIRSPACE WHILE IN CPDLC COM WITH ATC.

Narrative: SBOUND APCHING INTXN IN OCEANIC AIRSPACE. WE HAD ALREADY BEEN APPROVED FOR A 20 NM R DEV (W). WE SUBSEQUENTLY REQUESTED THROUGH CPDLC A FURTHER DEV UP TO 40 NM R FOR WX AVOIDANCE. OUR REQUEST TO DEVIATE WAS INITIALLY DENIED. AT THE TIME; WE OBSERVED ONLY 1 ACFT ON THE TCAS; 1000 FT ABOVE OUR ALT AND 20 NM L (E). USING CPDLC INPUTS WE DECLARED AN EMER AND USING CAPT'S EMER AUTH BEGAN TO DEVIATE UP TO 40 NM R (W) AROUND CONVECTIVE WX AT OUR ALT THAT EXTENDED 35 NM W OF TRACK AND 40 NM E. THERE WERE NO ADDITIONAL ACFT ON OUR TCAS SCREEN. ZZZ QUICKLY RESPONDED WITH CLRNC TO DEVIATE UP TO 40 NM R OF TRACK AND ASKED THAT WE RPT BACK ON COURSE. WE COMPLIED WITH THE AMENDED CLRNC; CANCELED THE EMER; AND RPTED BACK ON COURSE. THE FLT CONTINUED TO DEST WITHOUT FURTHER DEVELOPMENT.

Data retrieved from NASA's ASRS site as of January 2009 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.