Narrative:

During flight on oceanic airway flight encountered a twring thunderstorm that exceeded the aircraft's altitude and showed a high degree of reflectivity and intensity on the radar. Well before reaching the cell, I called ZZZ radio and informed them of our need to deviate west of track to avoid the build-up. ZZZ radio told us to standby. We finally reached a point where we needed to exercise our good judgement and emergency authority/authorized and maneuver the aircraft to avoid penetrating the cell. Captain declared his emergency authority/authorized over the HF radio to ZZZ and we deviated to the west off course to avoid the storm. ZZZ radio acknowledged captain's call declaring his emergency authority/authorized and had no further comment on the incident to us at that time.

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Original NASA ASRS Text

Title: FLT CREW OF B757-200 EXERCISE EMER AUTH TO AVOID WX ENRTE TO ZZZ, FO.

Narrative: DURING FLT ON OCEANIC AIRWAY FLT ENCOUNTERED A TWRING TSTM THAT EXCEEDED THE ACFT'S ALT AND SHOWED A HIGH DEG OF REFLECTIVITY AND INTENSITY ON THE RADAR. WELL BEFORE REACHING THE CELL, I CALLED ZZZ RADIO AND INFORMED THEM OF OUR NEED TO DEVIATE W OF TRACK TO AVOID THE BUILD-UP. ZZZ RADIO TOLD US TO STANDBY. WE FINALLY REACHED A POINT WHERE WE NEEDED TO EXERCISE OUR GOOD JUDGEMENT AND EMER AUTH AND MANEUVER THE ACFT TO AVOID PENETRATING THE CELL. CAPT DECLARED HIS EMER AUTH OVER THE HF RADIO TO ZZZ AND WE DEVIATED TO THE W OFF COURSE TO AVOID THE STORM. ZZZ RADIO ACKNOWLEDGED CAPT'S CALL DECLARING HIS EMER AUTH AND HAD NO FURTHER COMMENT ON THE INCIDENT TO US AT THAT TIME.

Data retrieved from NASA's ASRS site as of July 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.