Date: 201301
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Oxygen System/Crew
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Human factors: Training / Qualification; Distraction; Confusion; Situational Awareness; Workload
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew; Person Maintenance
When detected: Aircraft In Service At Gate; In-flight
Result: Flight Crew Diverted; General Maintenance Action
Contributing factors: Weather; Procedure; Human Factors; Aircraft; Environment - Non Weather Related
Primary problem: Ambiguous

Narrative: We left the hotel slightly early on our ride to the airport to allow extra time for inclement weather that had fallen overnight (light freezing rain; snow pellets and approximately 2 inches of snow). Upon entering the cockpit there were 2 individuals seated in the pilot seats. They identified themselves as our Mechanics and that they had attempted 2 APU starts; each of which failed due to an auto-APU shutdown. As the Captain and I began to get settled into the cockpit we both noticed that the RMP power switches had been turned off which we had not turned off the day before. I went outside to conduct my normal exterior preflight duties. When I returned to the cockpit the Captain and I discussed the 2 APU auto-shutdowns for a short time and a call was made to Maintenance Control to inquire about any possible causes and/or remedies. At Maintenance Control's direction we 'cycled' the battery switches and the APU started normally. The Maintenance Personnel then informed us that the cold weather ops check had not been performed on the overnight but during my walk-around inspection I had noticed that the outflow valve was partially closed and upon returning to the cockpit I saw that the pressurization system was in the manual (MAN) position. The maintenance red card was on the throttle quadrant and after inquiring with the station Maintenance personnel they told us that the card could be removed. I completed my cockpit preflight duties and did not note any discrepancies. Once again I cannot remember the actual O2 mask test; all I can say is that; part of my cockpit setup flow does include the test. The Captain has indicated that he remembers me performing the test in during preflight. During cruise and approximately 3 hours into the flight the Captain and I were making arrangements with the flight attendants to setup for a physiological break. The Captain donned his O2 mask in preparation for me to leave my pilot station and then noted that the crew O2 bottle pressure had depleted to approximately 20 to 40 psi. We called the Flight Attendant to inform them that we would not be taking a break at this time due to a system discrepancy that we needed to sort out. After some discussion with the Captain we decided to descend to FL250 and contact the company for further guidance. It was jointly decided that a diversion was the best course of action. We conducted the diversion with no issues and landed safely sometime later. Upon arrival the maintenance personnel gained access to the crew O2 bottle and determined in a very short period of time that the ON/OFF valve on the bottle was in the OFF position. We completed all necessary paperwork and following a thorough ops check of the crew O2 system it was determined that it was functional and we then departed on our continuing flight without any further issues. In the future when I test the O2 masks I will perform the test for a much longer period of time to ensure that that O2 is in fact coming from the bottle and not just the residual line pressure.


Second narrative: We noticed the O2 was very low and we had an advisory message about 2 and a half hour into the flight. The First Officer needed to use the restroom. I took my O2 mask out and inflated it but did not put it on. When the First Officer got up to verify the door I went to put on the mask and noticed the advisor message for the O2. I squeezed the red handles again and got the low regulator message on the door page. I asked the First Officer to return to his seat and advised the flight attendants that we a minor issue to deal with. The ECAM gave only an advisory. We looked it up in Volume 2 Chapter 4 under advisories and it leads us to systems which did not give any new information. I called Maintenance on SELCAL to advice of our situation. We did not have a very good connection and I had a difficult time understanding them. While I was talking to Maintenance I asked the First Officer to descend to 25;000 feet. My thinking was if we did have a problem we would be able to get to a better altitude quicker. This altitude was chosen for the O2 requirements of 1 pilot at his station. While I was waiting for further communication with Maintenance Control the connection was lost. I continued to monitor SELCAL. We received an ACARS message from Dispatch advising us to divert to a nearby airport because our filed destination did not have the ability to service O2. We then diverted following the procedure in Volume 1 for an international Divert to a US city. After we landed and we able to get off the aircraft we talked with the Mechanic and he advised us that the O2 valve had been shutoff. We then continued to our destination after all the paperwork was completed. I was completely surprised by the valve being off. I know for a fact that I did an O2 check the previous day. I also distinctly remember the First Officer doing an O2 check during preflight. I do not recall actually doing my check; however I am very confident that I did it. It is part of a flow that I do many times over. I also don't remember turning on the seatbelt sign or the ground recorder but they were ON.


Synopsis: An A319 crew discovered in cruise flight that the flight station O2 supply was low and so diverted where Maintenance discovered the O2 system valve had been closed and not reopened during preflight.