Flight Crew Air Transport Pilot (ATP)
Flight Crew Type 2746.98
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action
Aircraft; Equipment / Tooling
During my preflight; I had confirmed that the Crew Oxygen level was at 1200 PSI. Enroute I wrote up the Captain's O2 Mask Housing needs [to be] secured. Maintenance corrected the housing [at our enroute stop]. I noted that the O2 level had decreased below 1000 PSI. Enroute to [next destination]; at FL320 I noted that the O2 level had decreased to below 500 PSI. Checking the limitations section of the FM; I saw that the level was below that required for Dispatch. I notified [Maintenance] on ACARS and submitted a [maintenance] code for low Crew Oxygen pressure. My FO and I discussed possibly flying at a lower altitude due to the depleting Oxygen supply. We brought [Dispatch] into the conversation. The [Flight Operations Manager] immediately joined the conversation. Together we agreed that the best course of action was a diversion to land [at a nearby alternate]. We notified ATC and received a clearance [to the alternate]. I notified the flight attendants and the passengers. We landed uneventfully.Coincidentally; this is my second B737 Crew Oxygen issue in a month. I started a trip earlier in the month and found an airplane with [zero] Crew Oxygen pressure.
B737 NG Captain reported diverting to an alternate when the crew oxygen pressure dropped below 500 PSI while enroute.