Flight crew of B737-700 fail to note drop in oxygen pressure during preflight checks. They are infor...

Attributes
ACN	676876
Time
Date	200510
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Environment
Flight Conditions	VMC
Light	Dawn
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	ground : maintenance ground : preflight
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 174 flight time total : 8000 flight time type : 5500
ASRS Report	676876
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 176 flight time type : 11000
ASRS Report	676231
Events
Anomaly	aircraft equipment problem : critical maintenance problem : improper maintenance non adherence : published procedure
Independent Detector	other other : 3
Resolutory Action	none taken : detected after the fact
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft Maintenance Human Performance
Primary Problem	Maintenance Human Performance

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.

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.

Flight crew of B737-700 fail to note drop in oxygen pressure during preflight checks. They are informed maintenance failed to completely open valve after bottle replacement.