B737-800
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Aircraft; Human Factors; Procedure
Aircraft had an MEL 35-02A placard which pertains to the flight deck crew oxygen indicator being inoperative.  It requires a Maintenance inspection every flight to ensure that the oxygen bottle has enough oxygen for the number of pilots on the flight deck for the flight. What this MEL does not cover is a serious question as to whether the oxygen valve on the bottle is fully open.  Those of you that were 737 pilots will recall a period where we had discovered airplanes with the valve not fully open and will understand the magnitude of this oversight.When performing preflight duties the pilots are required to check for a pressure drop on the oxygen indicator. If the needle stays steady you were confident the valve was open.  With the oxygen gage being inoperative this safety feature is removed.  MEL 35-02A does not address this at all; it only addresses the bottle being full. Therefore I am requesting that along with the bottle quantity being confirmed that we add the oxygen bottle valve be checked to confirm in the full open position to the MEL. This is an essential item of safety.
The reporter stated that the issue of the crew O2 supply not completely turned on has been going on for a long time. The reporter stated that when the O2 indicator is deferred it is unknown to the crew if the valve is completely open or not. The reporter also stated that they (the flight crew) will get Maintenance to come out and verify that the O2 valve is completely open. The reporter stated that when the crew O2 is serviced they would like to see two signatures verifying that the valve is completely open. The reporter stated that this issue has been pursued for quite some time and has not seen any action on it.
B737 Captain reported they are unable to confirm if the O2 system is operating properly if the gauge is inoperative.