Narrative:

In cruise at FL360 on nat track system. The captain went to cabin for a few mins and first officer donned oxygen mask. After a few mins, his mask went dead. We then discovered that although the oxygen bottle was showing normal pressure, no oxygen was getting to the cockpit. We descended right away to FL290, and tried to work with the oxygen shutoff valve in the cockpit. After our efforts were unsuccessful, we descended to 14000 ft and diverted to ZZZ where repairs were made. Callback conversation with reporter revealed the following information: the reporter stated the airplane was a B747-200 and was overwater near greenland. The reporter said when he left the cockpit for a moment and the first officer donned the oxygen mask it was discovered no oxygen flow was coming through the mask. The reporter stated the regulators, and cockpit shutoff valves were checked and the bottle indicator showed full and all attempts failed to get oxygen flow to any masks. The reporter said an emergency descent to 14000 ft was made and a diversion to ZZZ initiated. The reporter stated at ZZZ the oxygen system was repaired by replacement of the bottle regulator and cockpit shutoff valve. The reporter said the system then tested ok.

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Original NASA ASRS Text

Title: A B747-200 IN CRUISE AT FL360 MADE AN EMER DSCNT TO 14000 FT AND DIVERTED DUE TO FAILURE OF OXYGEN FLOW TO ALL COCKPIT MASKS.

Narrative: IN CRUISE AT FL360 ON NAT TRACK SYS. THE CAPT WENT TO CABIN FOR A FEW MINS AND FO DONNED OXYGEN MASK. AFTER A FEW MINS, HIS MASK WENT DEAD. WE THEN DISCOVERED THAT ALTHOUGH THE OXYGEN BOTTLE WAS SHOWING NORMAL PRESSURE, NO OXYGEN WAS GETTING TO THE COCKPIT. WE DSNDED RIGHT AWAY TO FL290, AND TRIED TO WORK WITH THE OXYGEN SHUTOFF VALVE IN THE COCKPIT. AFTER OUR EFFORTS WERE UNSUCCESSFUL, WE DSNDED TO 14000 FT AND DIVERTED TO ZZZ WHERE REPAIRS WERE MADE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE AIRPLANE WAS A B747-200 AND WAS OVERWATER NEAR GREENLAND. THE RPTR SAID WHEN HE LEFT THE COCKPIT FOR A MOMENT AND THE FO DONNED THE OXYGEN MASK IT WAS DISCOVERED NO OXYGEN FLOW WAS COMING THROUGH THE MASK. THE RPTR STATED THE REGULATORS, AND COCKPIT SHUTOFF VALVES WERE CHKED AND THE BOTTLE INDICATOR SHOWED FULL AND ALL ATTEMPTS FAILED TO GET OXYGEN FLOW TO ANY MASKS. THE RPTR SAID AN EMER DSCNT TO 14000 FT WAS MADE AND A DIVERSION TO ZZZ INITIATED. THE RPTR STATED AT ZZZ THE OXYGEN SYS WAS REPAIRED BY REPLACEMENT OF THE BOTTLE REGULATOR AND COCKPIT SHUTOFF VALVE. THE RPTR SAID THE SYS THEN TESTED OK.

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.