Training / Qualification; Human-Machine Interface
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Aircraft; Procedure
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.
The Reporter stated that his personal oxygen preflight test is slightly more extensive than his Company's published preflight procedure. Because the oxygen bottle and valve are located in the forward baggage compartment; there is no way to access it and physically check the valve's position. So to ensure the oxygen is available; he holds the oxygen mask test for at least seven seconds while looking directly at the gauge to ensure pressure is maintained and at the same time tests the mask's micophone. The Chief Pilot's statement that the oxygen was in fact OFF has the Reporter puzzled because he remembers testing the oxygen in his usual manner that day.
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.