Narrative:

I was informed today; nov/mon/05; at XA35; of a possible oxygen malfunction in aircraft X flown by us 2 weeks ago. The oxygen valve was found partially closed after another crew wrote up the jet for a 5 psi drop during their oxygen test during preflight. We started the morning as an originator. I tested the oxygen system per our SOP guidance and received normal indications. I held the reset lever and emergency/test selector for a minimum of 5 seconds. I usually hold the test for anywhere from 5-10 seconds. I did not see a drop in pressure. Follow-on tests at 2 other cities checked normal for air flow; but I did not check the pressure since it checked normally during my first check of the day. My first officer doesn't recall checking the oxygen pressure; but had positive flow during his oxygen checks. I was surprised to hear the aircraft had an oxygen problem because I'm sure I had a good oxygen check on that aircraft. I religiously check my oxygen system and don't think I could have missed an oxygen psi drop. Possibly; the pressure built up overnight to give a normal reading during the first test of the day. I did not check the pressure readings on subsequent checks since the first check was normal. Maybe I need/should check the psi on all tests; but fom guidance states on originating flts.

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Original NASA ASRS Text

Title: FLT CREW OF B737-700 FAIL TO NOTE DROP IN OXYGEN PRESSURE DURING PREFLT CHKS. THEY ARE INFORMED MAINT FAILED TO COMPLETELY OPEN VALVE AFTER BOTTLE REPLACEMENT.

Narrative: I WAS INFORMED TODAY; NOV/MON/05; AT XA35; OF A POSSIBLE OXYGEN MALFUNCTION IN ACFT X FLOWN BY US 2 WKS AGO. THE OXYGEN VALVE WAS FOUND PARTIALLY CLOSED AFTER ANOTHER CREW WROTE UP THE JET FOR A 5 PSI DROP DURING THEIR OXYGEN TEST DURING PREFLT. WE STARTED THE MORNING AS AN ORIGINATOR. I TESTED THE OXYGEN SYS PER OUR SOP GUIDANCE AND RECEIVED NORMAL INDICATIONS. I HELD THE RESET LEVER AND EMER/TEST SELECTOR FOR A MINIMUM OF 5 SECONDS. I USUALLY HOLD THE TEST FOR ANYWHERE FROM 5-10 SECONDS. I DID NOT SEE A DROP IN PRESSURE. FOLLOW-ON TESTS AT 2 OTHER CITIES CHKED NORMAL FOR AIR FLOW; BUT I DID NOT CHK THE PRESSURE SINCE IT CHKED NORMALLY DURING MY FIRST CHK OF THE DAY. MY FO DOESN'T RECALL CHKING THE OXYGEN PRESSURE; BUT HAD POSITIVE FLOW DURING HIS OXYGEN CHKS. I WAS SURPRISED TO HEAR THE ACFT HAD AN OXYGEN PROB BECAUSE I'M SURE I HAD A GOOD OXYGEN CHK ON THAT ACFT. I RELIGIOUSLY CHK MY OXYGEN SYS AND DON'T THINK I COULD HAVE MISSED AN OXYGEN PSI DROP. POSSIBLY; THE PRESSURE BUILT UP OVERNIGHT TO GIVE A NORMAL READING DURING THE FIRST TEST OF THE DAY. I DID NOT CHK THE PRESSURE READINGS ON SUBSEQUENT CHKS SINCE THE FIRST CHK WAS NORMAL. MAYBE I NEED/SHOULD CHK THE PSI ON ALL TESTS; BUT FOM GUIDANCE STATES ON ORIGINATING FLTS.

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