Narrative:

While on the track my international relief officer noticed that the flight deck crew oxygen supply had decreased since his last aircraft systems check. After cross referencing with the minimum flight crew oxygen pressure table we determined we were approaching the minimum pressure. I turned the aircraft off the track and the first officer began coordinating with ATC for a diversion. At the time of the beginning of the diversion we were less than 100 miles and several minutes from our 180 minute rule equal time point (etp). At 15 miles off track and heading 180 degrees parallel to the tracks I began an emergency decent to 10;000 feet. Below 28;000 feet we began heading direct to the divert airport per ATC clearance.at 10;000 feet; when we were no longer in an emergency situation; we contacted our dispatcher via sat communication. As a precaution; we shut off the oxygen supply to save the remaining oxygen (450 psi) in case of a subsequent smoke/fumes event.

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Original NASA ASRS Text

Title: An A330 Captain reported that the crew oxygen system had developed a leak; requiring a diversion to an en route airport.

Narrative: While on the track my IRO noticed that the flight deck crew oxygen supply had decreased since his last aircraft systems check. After cross referencing with the Minimum Flight Crew Oxygen Pressure Table we determined we were approaching the minimum pressure. I turned the aircraft off the track and the First Officer began coordinating with ATC for a diversion. At the time of the beginning of the diversion we were less than 100 miles and several minutes from our 180 minute rule Equal Time Point (ETP). At 15 miles off track and heading 180 degrees parallel to the tracks I began an emergency decent to 10;000 feet. Below 28;000 feet we began heading direct to the divert airport per ATC clearance.At 10;000 feet; when we were no longer in an emergency situation; we contacted our dispatcher via SAT COM. As a precaution; we shut off the oxygen supply to save the remaining oxygen (450 psi) in case of a subsequent smoke/fumes event.

Data retrieved from NASA's ASRS site 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.