Q400
Maintenance Airframe; Maintenance Powerplant
Situational Awareness
Aircraft Equipment Problem Critical
General Maintenance Action
Aircraft; Human Factors
I was given the task to replace the crew O2 bottle on a Q400 aircraft. I followed the Task Card and removed and replaced the bottle and checked both masks for proper operation and flow of O2. Later that night I went back and reinspected my installation of the O2 bottle just to be sure I was confident I had done everything correctly and had not missed anything. It all looked good so I closed the access panel and walked away. The next morning; the pilot checked for [oxygen] flow and heard the normal 'hiss' so he was satisfied and moved on down his checklist and flew out without incident. The next pilot to fly the aircraft apparently did not hear O2 flow when he performed his pre-flight so he notified Maintenance. Apparently they inspected the bottle and found one of the quick-disconnects to be disconnected at that time. They reconnected it and returned the aircraft to service as I understand it. I was told of this event by my Supervisor.I am not sure why this event occurred. It is a relatively easy task to perform and I double and in fact; triple checked my work on this task before my shift was over. Perhaps the quick-disconnect lock was not fully latched and it popped off in flight somehow; or someone else may have disconnected it while performing their inspection; (which I would say is not likely). Or perhaps there is something faulty with the connection fittings; (Again not likely; but who knows). I don't know what all actions other people had to do; but I was advised by my Supervisor to fill out a report. Suggest having a block on the Task Card to have a second Mechanic inspect the final installation. Have 'witness marks' painted on the quick disconnect connectors to ensure they are securely locked into position; similar to the electrical and hydraulic connectors upon installation. Graveyard [shift].
A day after replacing a Crew Oxygen (O2) bottle on a Q400 aircraft and re-attaching the Crew O2 masks quick-disconnect fittings; a Line Mechanic was informed by his Supervisor that one of the quick-disconnect fittings was found not connected at a downline station.