MD-83
Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Distraction; Communication Breakdown
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
General Release Refused / Aircraft Not Accepted
Manuals; Aircraft; Procedure
I was the assigned Captain. I was assigned an MD-80. During my pre-flight I noticed that the Crew O2 line pressure indicator was showing a value below the green arc. I called MX (Maintenance) and reported the problem. A mechanic came out and requested the logbook and the MEL book. After a few minutes he returned and said the indicator would be deferred using MEL 35-01. That MEL says that 'IF' the indicator is inoperative it can be deferred as long as the crew O2 masks test positive and the crew O2 bottle pressure is above 1300 PSI. That was the case so the mechanic said that this is a good deferral. I disagreed; because he never tested if the crew O2 line indicator is indeed inoperative. I told him that the needle moves just fine but it shows a line pressure value that is below the green arc. The mechanic said that it shows a bad value and must therefore be inoperative. Again; I disagreed. For all I knew the indicator was working fine and there is insufficient pressure in the line. As evidence I pointed out to logbook page from the day before where it was written up previously. That day MX replaced the O2 regulator and that fixed the discrepancy. What happened the day before was actually supporting my opinion that something else but NOT the crew O2 line indicator was malfunctioning. If the indicator was showing low and MX replaces the O2 regulator and then the indicator shows green it means that the indicator is just fine. However; MX insisted that they would not change the deferral despite that absolutely NO troubleshooting or testing had been done.I therefore refused the airplane since I was not willing to jeopardize the safety of my passengers and crew not knowing if there was enough O2 pressure available in case of a depressurization at high altitudes. What is more concerning that there is a test procedure in the maintenance manual that could have tested the pressure in the crew line. It is listed in the MD 80 AMM 35-10. But our MX department seems to be willing to rather dispatch in an unsafe condition with no troubleshooting and an MEL that was not even verified to be the correct one.MX should not look at the MEL book as the first and foremost solution to keep the airplane flying.  Before any MEL is applied they should be trying to troubleshoot and fix first. If that is not possible then at the very least they should make sure that the right deferral is being used and not just the 'convenient' one. And most importantly; they should put the safety of crew and passengers above on-time dispatch numbers which they obviously don't!
An MD-83 Captain refused an aircraft with an oxygen system low pressure reading after Maintenance deferred the gauge but did not troubleshoot the system for an anomaly other than the gauge.