Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 240; Flight Crew Total 18000; Flight Crew Type 1000
Physiological - Other
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Procedure; Aircraft
During my preflight cockpit setup; I tested the Crew Oxygen system. While depressing the 100%/Test button on the oxygen mask; I noticed that the Crew Oxygen pressure on the overhead panel indicated 0 PSI. When I released the press to test button; the pressure went back up to 1700 PSI. I checked the other two masks in the cockpit and found the same issue. I wrote up the issue and maintenance came out to check the oxygen bottle in the forward cargo compartment. The mechanic found that after servicing the day before; the oxygen bottle valve had only been cracked open; not fully opened. He corrected the situation and we verified proper operation of the crew oxygen system.
The Captain of a B737 discovered the crew oxygen system failed to maintain pressure during the pre-flight check. Maintenance found the bottle valve only cracked open. When fully opened the system checked properly.