A B737-700 first officer reported a series of flight crews flew an aircraft with the crew oxygen sys...

Narrative:

After my four-day trip and prior to my commute home; the chief pilot approached me in the crew room and informed me that an aircraft which I had flown several day before had been identified with an oxygen problem. He explained that the oxygen bottle had been turned off at some point. I explained that I performed all of my normal oxygen tests per the aom as I always do and noticed nothing abnormal. My process: on every flight; I accomplish a F.I.G. Test (flow; intercom; O2 gauge level) as part of my flow when I get to the oxygen system. I hold the intercom switch and depress the oxygen for five to six seconds to check for a drop in the oxygen gauge. Since we were scheduled to have the aircraft for five flights; I remember checking the level at 1400+; which would last us all day. I had no significant drop in the oxygen level when tested on that flight and no issues on each of the subsequent four flights. The only thing I can offer is: change the test (if data supports) it from five seconds to ten seconds or possibly both captain and first officer test the O2 at the same time to put more demand on it in the current five second recommended test procedure.

Original NASA ASRS Text

Title: A B737-700 First Officer reported a series of flight crews flew an aircraft with the crew oxygen system not energized but he is certain that he successfully tested the oxygen system prior to his first flight on that aircraft.

Narrative: After my four-day trip and prior to my commute home; the Chief Pilot approached me in the Crew Room and informed me that an aircraft which I had flown several day before had been identified with an oxygen problem. He explained that the oxygen bottle had been turned off at some point. I explained that I performed all of my normal oxygen tests per the AOM as I always do and noticed nothing abnormal. My Process: On every flight; I accomplish a F.I.G. Test (Flow; Intercom; O2 Gauge level) as part of my flow when I get to the oxygen system. I hold the intercom switch and depress the oxygen for five to six seconds to check for a drop in the oxygen gauge. Since we were scheduled to have the aircraft for five flights; I remember checking the level at 1400+; which would last us all day. I had no significant drop in the oxygen level when tested on that flight and no issues on each of the subsequent four flights. The only thing I can offer is: Change the test (if data supports) it from five seconds to ten seconds or possibly both Captain and First Officer test the O2 at the same time to put more demand on it in the current five second recommended test procedure.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1074805
Time
Date	201303
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Parked
Flight Plan	IFR
Component
Aircraft Component	Oxygen System/Crew
Person 1
Function	First Officer
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy

A B737-700 first officer reported a series of flight crews flew an aircraft with the crew oxygen system not energized but he is certain that he successfully tested the oxygen system prior to his first flight on that aircraft.