Date: 201707
Local time of day: 0601-1200
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Aircraft component: Oxygen System/Crew
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Communication Breakdown
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted
Contributing factors: Aircraft; Human Factors; Procedure
Primary problem: Aircraft

Narrative: After boarding was completed for our flight we pushed off the gate on time. The taxi out to runway was uneventful. The takeoff; climb and initial cruise portions of our flight were also uneventful. Approximately 2 hours into the flight we called back to the Flight Attendants to initiate a Lavatory Break. We discussed that as the Pilot Flying (PF) I would use the Lavatory first and the Captain (CA) second. While out on the Lavatory Break; I heard a loud whoosh noise from up in the Flight Deck. This noise caught my attention so I immediately called up to the Flight Deck to request entry back in. When I got back into my seat the CA was holding the oxygen hose and his mask together in his hands while we could hear a hissing sound. The CA explained that the Oxygen hose for his crew mask would not stay attached to the mask. At this point we initiated a positive exchange of control and I re-assumed control of the Aircraft as the Pilot Flying (PF). I then took hold of the mask and the Oxygen hose and attempted to hold them together to save as much crew oxygen as we could. As a crew we thought we would be able to put the mask and the hose back together to save the oxygen from leaking out. The CA made several attempts at re-securing the oxygen hose to the mask but did not succeed. I also made several attempts at securing the oxygen hose back to the oxygen mask. Due to the positive pressure of Oxygen coming from the hose; we were both unsuccessful at securing the Oxygen hose. After several minutes we became unable to even hold the oxygen hose to the mask. At this point there was nothing to even slow the flow of the crew oxygen and we began to lose crew oxygen at an extremely fast rate. When this event began we had just passed the point where our enroute alternate changed. As this event was unfolding; the CA and I started to discuss our options including other enroute alternate options. We notified [dispatch] of our situation right after it occurred; explained what our situation was and asked for a descent to FL250. We never got a definitive response from [dispatch]. After we heard the controller repeatedly contact other aircraft we asked again for an emergency descent down to FL250. [Dispatch] was still extremely slow to get back to us. This delay eliminated one of our divert options because we were starting to track away. Finally we decided that we could not wait any longer and needed to start down. We told ARINC that we were executing an emergency descent to FL250. On the way down we elected to continue down to FL230. Since one divert airport was no longer an option we elected to change our destination to the next divert Alternate airport due to the fact that we [were using an alternate means of communication] and could not communicate with the Company to receive an accurate fuel burn and time to our destination alternate at the lower altitude. ARINC then gave us a frequency to contact Center. We elected to continue the descent down to 14;000 as we were trying to formulate our game plan. We then maintained 14;000 feet until we were sure that we had adequate fuel to continue the flight to the Alternate. After repeatedly trying to contact Center on our VHF Radio and not getting a response we attempted to contact ARINC again on our HF radio. When even this didn't work we went back to trying to contact Center. While in the descent the CA and I utilized our CRM and decided on the tasks that we were to deal with. He began to speak to the Flight Attendants and Passengers and let them know what our situation was and that we were headed to the Alternate airport. While the CA was doing this I was continuing to fly the aircraft but also still trying to reach Center on the assigned frequency as well as on 121.5. After multiple attempts to Center; I heard two other aircraft on guard informing Center that we were trying to reach them. I then contacted the other aircraft on guard and asked them to relay to Center our descent; problem; where we wantedto go and that we had been unable to make contact with them on the assigned frequency. One aircraft continued to assist us by relaying our position and status to Center until we were able to reach VHF range. After we changed our destination to our enroute Alternate; and things started to calm down; we realized that we were still [not communicating]. This brought up the point that we were unable to receive landing information from the ACARS as well as other messages from dispatch. We saw that the runway was 6;000 long. Discussing our options the CA and I agreed that this Alternate was not a good option for us. We elected to change our destination due to its 10;000 foot runway and that it also had company Services and support due to it being a line station. At some point during the descent we also noted that the Crew Oxygen Bottle had completely emptied itself and was now reading 0 psi. Upon arrival we immediately contacted Operations and asked for a phone; which we then called Company Maintenance Control and Operations. During the flight the CA repeatedly asked ATC multiple times to contact the company due to the fact that we were NO COMM and could not reach the company. After speaking with the company the CA said that ATC never called the company and that they had only sent a couple of messages. Maintenance came out to the plane and we explained to them what happened. We sat on the ground for approx. 2 hours when we were finally informed that the aircraft could not be fixed and that a rescue aircraft was on its way down to pick up our Passengers. Maintenance replaced the Oxygen bottle overnight and the CA and I ferried the flight back the next morning.




Synopsis: B737 First Officer reported that the one of the flight crew's oxygen masks became separated from its oxygen feeder hose; resulting in oxygen escaping from the disconnected hose resulted in complete loss of aircrew oxygen supply. The crew diverted to an alternate airport.