Faced with the likely eventual complete loss of crew oxygen while two hours into a transpacific flig...

Attributes
ACN	814431
Time
Date	200812
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : oak.airport
State Reference	CA
Altitude	msl single value : 35000
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B777-200
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : relief pilot
Experience	flight time last 90 days : 220 flight time total : 10000 flight time type : 2000
ASRS Report	814431
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : crew o2 press gauge other flight crewa
Resolutory Action	flight crew : declared emergency flight crew : exited adverse environment
Supplementary
Problem Areas	Aircraft Environmental Factor
Primary Problem	Aircraft

Narrative:

About 2 hours into our flight from hnl; I was called up to the flight deck from my rest break. I was informed by the flying crew that the crew oxygen pressure was depleting. At this point the pressure was about 550 psi. The emergency procedure checklist directed that once the pressure dropped to 500 psi or less; an immediate descent was required. The crew had already contacted dispatch and maintenance and they were aware of the problem. We contacted ATC and requested a return to hnl. We initially attempted contact on cpdlc but had a delay getting a clearance. We called commercial radio on HF and subsequently received a clearance over HF to proceed direct puppi direct sok direct hnl. We later found out that the reason we could not get a clearance on cpdlc is because ATC was having computer problems. After receiving clearance; we made a r-hand turn to proceed direct to puppi. The turn placed us about 15 mi offset from track a. While proceeding direct ti puppi our crew oxygen pressure dropped to 0PSI. We attempted to get clearance for an immediate descent to 10000 ft. There was a delay in receiving clearance; so the captain exercised his emergency authority/authorized and initiated a descent to 10000 ft. Eventually; clearance was obtained for our descent. We continued on to hnl at 10000 ft for an uneventful approach and landing.

Original NASA ASRS Text

Title: FACED WITH THE LIKELY EVENTUAL COMPLETE LOSS OF CREW OXYGEN WHILE TWO HOURS INTO A TRANSPACIFIC FLIGHT; B777-200 FLIGHT CREW ELECTS TO RETURN TO DEPARTURE AIRPORT. THEY LATER DESCEND TO 10;000 FEET ON CAPTAIN'S EMERGENCY AUTHORITY WHEN O2 PRESSURE DROPS TO ZERO.

Narrative: ABOUT 2 HRS INTO OUR FLT FROM HNL; I WAS CALLED UP TO THE FLT DECK FROM MY REST BREAK. I WAS INFORMED BY THE FLYING CREW THAT THE CREW OXYGEN PRESSURE WAS DEPLETING. AT THIS POINT THE PRESSURE WAS ABOUT 550 PSI. THE EMER PROC CHKLIST DIRECTED THAT ONCE THE PRESSURE DROPPED TO 500 PSI OR LESS; AN IMMEDIATE DSCNT WAS REQUIRED. THE CREW HAD ALREADY CONTACTED DISPATCH AND MAINT AND THEY WERE AWARE OF THE PROB. WE CONTACTED ATC AND REQUESTED A RETURN TO HNL. WE INITIALLY ATTEMPTED CONTACT ON CPDLC BUT HAD A DELAY GETTING A CLRNC. WE CALLED COMMERCIAL RADIO ON HF AND SUBSEQUENTLY RECEIVED A CLRNC OVER HF TO PROCEED DIRECT PUPPI DIRECT SOK DIRECT HNL. WE LATER FOUND OUT THAT THE REASON WE COULD NOT GET A CLRNC ON CPDLC IS BECAUSE ATC WAS HAVING COMPUTER PROBS. AFTER RECEIVING CLRNC; WE MADE A R-HAND TURN TO PROCEED DIRECT TO PUPPI. THE TURN PLACED US ABOUT 15 MI OFFSET FROM TRACK A. WHILE PROCEEDING DIRECT TI PUPPI OUR CREW OXYGEN PRESSURE DROPPED TO 0PSI. WE ATTEMPTED TO GET CLEARANCE FOR AN IMMEDIATE DESCENT TO 10000 FT. THERE WAS A DELAY IN RECEIVING CLRNC; SO THE CAPT EXERCISED HIS EMER AUTH AND INITIATED A DSCNT TO 10000 FT. EVENTUALLY; CLRNC WAS OBTAINED FOR OUR DSCNT. WE CONTINUED ON TO HNL AT 10000 FT FOR AN UNEVENTFUL APCH AND LNDG.

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

Faced with the likely eventual complete loss of crew oxygen while two hours into a transpacific flight; B777-200 flight crew elects to return to departure airport. They later descend to 10;000 feet on captain's emergency authority when O2 pressure drops to zero.