A300
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Situational Awareness; Communication Breakdown; Troubleshooting
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Overcame Equipment Problem; General Maintenance Action
MEL; Aircraft; Human Factors; Procedure
After takeoff in ZZZ; went to retract the gear with it in system 1; gear would not come up. We then followed the ECAM (Electronic Centralized Aircraft Monitor) and QRH and were directed to swap to system 2. Gear retracted normally in system 2.  After that; we remembered that system 2 was on MEL.  We discussed this enroute and elected to continue to ZZZ1. The flight continued with a normal landing.After getting the ECAM warning; we followed the ECAM and QRH as directed like we normally would under this circumstance. We swapped to system 2 and retracted the gear normally.  We then continued the flight.
On departure from ZZZ landing retraction system! was system used on takeoff; gear would not retract. We followed ECAM and QRH and instinctively switched to system 2 and raised the gear and continued flight. While enroute we discussed that system 2 was in MEL although system worked normal. Continued to ZZZ1 with normal landing.Out of normal habit to follow ECAM and QRH while in busy phase of flight we switched retract position to system 2 and gear retracted.
A300 flight crew reported the landing gear would not retract using system 1 and elected to use system two to retract the landing gear. Flight crew further reported that after landing; they observed that system 2 was deferred and was not to be used.