Narrative:

Preflight of crew oxygen system consisted of the 'first flight of the day' checks. Oxygen pressure indicated 1100 psi (ok for dispatch) preflight checks were all noted to be operational. Check consisted of microphone and airflow check with slight dip in oxygen pressure indicator of +/-50 psi. First officer left the cockpit for a bathroom break and the flight attendant took her position in the cockpit as SOP required. I attempted to put crew oxygen on and it inflated slightly and I noticed a pressure drop approximately 500 psi; second attempt depleted the system to less than 100 psi. Crew oxygen system is inoperative. I advised the flight attendant in cockpit to call back to flight attendants and bring 2 pob's up to the cockpit immediately. The first officer called the cockpit to enter with the pob's. I briefed the first officer as to the situation and we tested the pob's and had them in the 'ready to use position' should the need arise. Meanwhile; I was already engaged in a higher than normal descent rate into ZZZZ. The first officer attempted to troubleshoot with no success; we referred to the QRH but we found no checklist for the problem we had encountered. The descent to a safer altitude and the pob's on hand was our supplement checklist. I sent a maintenance message to maintenance control to expedite the corrective action. Upon landing and after the postflt checklists; I wrote the crew oxygen system up in the logbook as stated; 'crew oxygen needs to be recharged to preflight status.' I met the crew and briefed them as to our experience and contract maintenance was called in to fix the problem. I later found out that the maintenance had failed to open the crew oxygen valve in the east&east compartment. The residual pressure in the lines gave us a satisfactory preflight check however; we proved that our crew oxygen checklist needs to be altered. The; 'push to test' portion of our test needs to be increased from 5 seconds to 10 seconds. This additional time would ensure any residual pressure in the lines would be eliminated/removed should the valve be inadvertently closed. Callback conversation with reporter revealed the following information: reporter stated their carrier has some next gen aircraft that use steel oxygen bottles; not just composite type. But; the composite bottles seem to be the focus of concern due to the test procedure for the 'press to test ' oxygen mask supply may not be adequate enough for the flight crew to identify an actual low flow in the supply line from a valve handle not fully opened. Other carriers; including his; have a minimum 5-SECOND 'press to test' procedure in their flight operations manual. But; there is a feeling the 5-SECOND flow test needs to be expanded to 10-seconds. Reporter also stated their B737-800's do not have a crew oxygen shut-off valve in the cockpit; only in the lower east/east compartment at the bottle itself.

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Original NASA ASRS Text

Title: A B737-800 CAPTAIN REPORTS OF INFLIGHT CREW OXYGEN FLOW SUPPLY FAILURE. BELIEVES THE 5-SECOND MINIMUM OXYGEN MASK 'PRESS TO TEST' PROCEDURE IS NOT ADEQUATE AND SHOULD BE EXPANDED TO 10-SECONDS.

Narrative: PREFLT OF CREW OXYGEN SYS CONSISTED OF THE 'FIRST FLT OF THE DAY' CHKS. OXYGEN PRESSURE INDICATED 1100 PSI (OK FOR DISPATCH) PREFLT CHKS WERE ALL NOTED TO BE OPERATIONAL. CHK CONSISTED OF MIKE AND AIRFLOW CHK WITH SLIGHT DIP IN OXYGEN PRESSURE INDICATOR OF +/-50 PSI. FO LEFT THE COCKPIT FOR A BATHROOM BREAK AND THE FLT ATTENDANT TOOK HER POS IN THE COCKPIT AS SOP REQUIRED. I ATTEMPTED TO PUT CREW OXYGEN ON AND IT INFLATED SLIGHTLY AND I NOTICED A PRESSURE DROP APPROX 500 PSI; SECOND ATTEMPT DEPLETED THE SYS TO LESS THAN 100 PSI. CREW OXYGEN SYS IS INOP. I ADVISED THE FLT ATTENDANT IN COCKPIT TO CALL BACK TO FLT ATTENDANTS AND BRING 2 POB'S UP TO THE COCKPIT IMMEDIATELY. THE FO CALLED THE COCKPIT TO ENTER WITH THE POB'S. I BRIEFED THE FO AS TO THE SITUATION AND WE TESTED THE POB'S AND HAD THEM IN THE 'READY TO USE POS' SHOULD THE NEED ARISE. MEANWHILE; I WAS ALREADY ENGAGED IN A HIGHER THAN NORMAL DSCNT RATE INTO ZZZZ. THE FO ATTEMPTED TO TROUBLESHOOT WITH NO SUCCESS; WE REFERRED TO THE QRH BUT WE FOUND NO CHKLIST FOR THE PROB WE HAD ENCOUNTERED. THE DSCNT TO A SAFER ALT AND THE POB'S ON HAND WAS OUR SUPPLEMENT CHKLIST. I SENT A MAINT MESSAGE TO MAINT CTL TO EXPEDITE THE CORRECTIVE ACTION. UPON LNDG AND AFTER THE POSTFLT CHKLISTS; I WROTE THE CREW OXYGEN SYS UP IN THE LOGBOOK AS STATED; 'CREW OXYGEN NEEDS TO BE RECHARGED TO PREFLT STATUS.' I MET THE CREW AND BRIEFED THEM AS TO OUR EXPERIENCE AND CONTRACT MAINT WAS CALLED IN TO FIX THE PROB. I LATER FOUND OUT THAT THE MAINT HAD FAILED TO OPEN THE CREW OXYGEN VALVE IN THE E&E COMPARTMENT. THE RESIDUAL PRESSURE IN THE LINES GAVE US A SATISFACTORY PREFLT CHK HOWEVER; WE PROVED THAT OUR CREW OXYGEN CHKLIST NEEDS TO BE ALTERED. THE; 'PUSH TO TEST' PORTION OF OUR TEST NEEDS TO BE INCREASED FROM 5 SECONDS TO 10 SECONDS. THIS ADDITIONAL TIME WOULD ENSURE ANY RESIDUAL PRESSURE IN THE LINES WOULD BE ELIMINATED/REMOVED SHOULD THE VALVE BE INADVERTENTLY CLOSED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THEIR CARRIER HAS SOME NEXT GEN ACFT THAT USE STEEL OXYGEN BOTTLES; NOT JUST COMPOSITE TYPE. BUT; THE COMPOSITE BOTTLES SEEM TO BE THE FOCUS OF CONCERN DUE TO THE TEST PROCEDURE FOR THE 'PRESS TO TEST ' OXYGEN MASK SUPPLY MAY NOT BE ADEQUATE ENOUGH FOR THE FLIGHT CREW TO IDENTIFY AN ACTUAL LOW FLOW IN THE SUPPLY LINE FROM A VALVE HANDLE NOT FULLY OPENED. OTHER CARRIERS; INCLUDING HIS; HAVE A MINIMUM 5-SECOND 'PRESS TO TEST' PROCEDURE IN THEIR FLT OPS MANUAL. BUT; THERE IS A FEELING THE 5-SECOND FLOW TEST NEEDS TO BE EXPANDED TO 10-SECONDS. REPORTER ALSO STATED THEIR B737-800'S DO NOT HAVE A CREW OXYGEN SHUT-OFF VALVE IN THE COCKPIT; ONLY IN THE LOWER E/E COMPARTMENT AT THE BOTTLE ITSELF.

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.