Narrative:

WX deviation left 30 NM at FL350. Sent data link request to deviate left 30 NM approaching intersection. Required to deviate prior to receipt of clearance through data link. At 10 NM offset; descended to FL347 per oceanic procedure as flying to 30 NM offset. Just prior to reaching 30 NM left; received ATC clearance as requested by data link. Advised ATC of altitude deviation per captain's emergency authority/authorized; later advised dispatch at XA01Z per operations manual. No traffic conflict or other issues. Supplemental information from acn 700558: noticed WX on track around intersection. Requested deviation 30 NM left of course using data link system. It became necessary to deviate prior to receiving clearance from ATC; so we elected to begin deviation following chart deviation procedures exercising captain's emergency authority/authorized to do so. Deviated left 10 NM and descended 300 ft per guidance. We later received clearance to deviate 30 NM. Shortly after that; ATC said a position report indicated we were 300 ft low. We responded that we had used captain's emergency authority/authorized to begin the deviation prior to receiving clearance.

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Original NASA ASRS Text

Title: A B777 CREW IN OCEANIC AIRSPACE USED CAPT'S EMER AUTH TO DEVIATE AROUND TSTMS WHEN THE DATA LINK CLRNC AUTHORIZING THE DEV WAS LATE ARRIVING.

Narrative: WX DEV L 30 NM AT FL350. SENT DATA LINK REQUEST TO DEVIATE L 30 NM APCHING INTXN. REQUIRED TO DEVIATE PRIOR TO RECEIPT OF CLRNC THROUGH DATA LINK. AT 10 NM OFFSET; DSNDED TO FL347 PER OCEANIC PROC AS FLYING TO 30 NM OFFSET. JUST PRIOR TO REACHING 30 NM L; RECEIVED ATC CLRNC AS REQUESTED BY DATA LINK. ADVISED ATC OF ALTDEV PER CAPT'S EMER AUTH; LATER ADVISED DISPATCH AT XA01Z PER OPS MANUAL. NO TFC CONFLICT OR OTHER ISSUES. SUPPLEMENTAL INFO FROM ACN 700558: NOTICED WX ON TRACK AROUND INTXN. REQUESTED DEV 30 NM L OF COURSE USING DATA LINK SYS. IT BECAME NECESSARY TO DEVIATE PRIOR TO RECEIVING CLRNC FROM ATC; SO WE ELECTED TO BEGIN DEV FOLLOWING CHART DEV PROCS EXERCISING CAPT'S EMER AUTH TO DO SO. DEVIATED L 10 NM AND DSNDED 300 FT PER GUIDANCE. WE LATER RECEIVED CLRNC TO DEVIATE 30 NM. SHORTLY AFTER THAT; ATC SAID A POS RPT INDICATED WE WERE 300 FT LOW. WE RESPONDED THAT WE HAD USED CAPT'S EMER AUTH TO BEGIN THE DEV PRIOR TO RECEIVING CLRNC.

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.