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.