B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 159; Flight Crew Type 10000
Situational Awareness; Troubleshooting
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Human Factors; Procedure
I flew a B737-700 aircraft. The following day; this aircraft would not give a proper test of the Oxygen System. It was reported by a Contract Mechanic that the valve on the oxygen bottle was not open. The bottle had last been replaced three days earlier. We did not notice any abnormal oxygen pressure readings during the preflight checks on the five legs that we flew the aircraft that day. I have preflighted an aircraft [before] with a 'Closed' oxygen valve. The pressure will read zero during the test and remain there. The facts of this event suggest to me that the valve on the oxygen bottle may have been only partially opened after installation. The inspecting Mechanic would have known this only if he attempted to close the valve as his first course of action during troubleshooting. [Recommend that] after installation of a new oxygen bottle; verification of normal pressure on the flight deck pressure gauge should be accomplished. The gauge will read zero until the bottle is opened. This may be [the] maintenance procedure currently. There is no procedure which; from the flight deck; which would necessarily reveal a partially opened oxygen valve.
O2 System checked normal.
Two pilots report about the Crew Oxygen System on their B737-700 aircraft that would not give a proper test after they had flown the aircraft for five legs. Contract Maintenance had reported the oxygen bottle valve handle was not open.