Narrative:

While performing our pre-flight duties in the morning we tested all the systems as required by the aom. Specifically when testing the crew oxygen system; the test was valid and the crew oxygen was deemed to be working fine and the test returned the expected results within parameters. The oxygen gauge showed a psi level of around 1;800 psi. We departed for ZZZ1 and arrived uneventfully ahead of our scheduled arrival time. Our trip was over at that point. Later in the evening of the same day; I received a phone call from the captain that took our airplane for the beginning of his trip. He called to advise that when they in turn did the oxygen test; their test showed a large drop in psi and an invalid test. When maintenance looked at the problem; they found that when the same airplane underwent maintenance the evening before in ZZZ; the crew oxygen bottle was swapped out and maintenance in ZZZ failed to open the crew oxygen valve all the way. Again; our [crew oxygen preflight] test in the morning showed a perfectly valid test and we continued as planned. Unfortunately; there may be no remedy on the B737 of avoiding a recurrence of this event as the pilots have no way of checking whether the oxygen valve is fully 'open' or not. The only way would be to notice a lack of psi on the oxygen gauge and in our situation it showed full. The overhead speaker test worked fine as well.

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Original NASA ASRS Text

Title: A Captain who had flown a B737-700 aircraft earlier in the day; was informed by an outbound Captain beginning their trip; that the Crew Oxygen (O2) on the same aircraft had a large drop in oxygen pressure when performing the Crew O2 Preflight Test. Maintenance found the Crew oxygen bottle valve handle was not opened all the way.

Narrative: While performing our pre-flight duties in the morning we tested all the systems as required by the AOM. Specifically when testing the Crew Oxygen System; the test was valid and the crew oxygen was deemed to be working fine and the test returned the expected results within parameters. The Oxygen gauge showed a PSI level of around 1;800 PSI. We departed for ZZZ1 and arrived uneventfully ahead of our scheduled arrival time. Our trip was over at that point. Later in the evening of the same day; I received a phone call from the Captain that took our airplane for the beginning of his trip. He called to advise that when they in turn did the Oxygen Test; their test showed a large drop in PSI and an invalid test. When Maintenance looked at the problem; they found that when the same airplane underwent maintenance the evening before in ZZZ; the Crew oxygen bottle was swapped out and Maintenance in ZZZ failed to open the Crew oxygen valve all the way. Again; our [Crew oxygen preflight] test in the morning showed a perfectly valid test and we continued as planned. Unfortunately; there may be no remedy on the B737 of avoiding a recurrence of this event as the pilots have no way of checking whether the oxygen valve is fully 'open' or not. The only way would be to notice a lack of PSI on the oxygen gauge and in our situation it showed full. The overhead speaker test worked fine as well.

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.