B737-800
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
General Flight Cancelled / Delayed; General Maintenance Action
Manuals; Aircraft; Human Factors
During preflight of Oxygen Mask/System; [crew] oxygen (O2) pressure dropped to zero then rebounded to 1200 PSI after TEST button released. Notified Maintenance who found O2 bottle improperly connected and SAFETY WIRED in partially 'Opened' position. Maintenance opened O2 bottle completely and re-safety wired it. I notified Dispatch via ACARS and asked him to query Maintenance Control about maintenance history on the O2 system; but there was no recent activity. Flight departed 18-minutes late. [Bottle handle] false indication.
Reporter stated his air carrier recently switched to a different crew O2 bottle Manufacturer (MFG) and suspects the new replacement bottles are composite. He does not know the name of the MFG. Their Pilot Safety Representative had recently alerted them through a video to the seriousness of crew O2 bottle shut-off handles being found not fully opened.Recommendations are to perform a 'Press to Test' of the crew O2 mask supply pressure for at least 5-7 seconds and observe the O2 pressure drop. That's how he noticed there was not enough O2 pressure being supplied to their crew O2 masks during their preflight. He suspects the problem may have been going on for a while until he did the longer test. Having the crew O2 bottle 'Open/Close' shut-off handle in the cockpit; like the older Classic B737s; may be more helpful; especially in flight.
Captain reports that during their preflight check on a B737-800 aircraft; the crew oxygen (O2) bottle pressure dropped to zero; then rebounded to 1200 PSI after crew O2 mask check Test button was released. Maintenance found O2 bottle 'Open/Close' handle safety-wired in the partially opened position.