Date: 202109
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: A321
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Airspace: Class B ZZZ
ATC / advisory: Ground ZZZ
Aircraft component: Cockpit/Cabin Communication
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown; Situational Awareness; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance
Detector: Person Flight Crew
When detected: Aircraft In Service At Gate
Result: General None Reported / Taken
Contributing factors: Aircraft; Human Factors; Logbook Entry; MEL; Procedure
Primary problem: Procedure

Narrative: After landing in ZZZ; we received a message from the out bound crew that an MEL on the aircraft may have been incorrect. I reviewed the release (rev0) and MELs before arriving at the aircraft in ZZZ1. At that time the only MELs where for the Rudder Limiter System; and more importantly MEL 23-XX-X for the CIDS (Cabin Intercommunication Display System) Director system. This MEL had no (O) procedures; and looked fairly straight forward. Upon arrival at the aircraft; Maintenance had the logbook and was in the process of deferring the Mid Lav. On the ECAM status page; in addition to the Rudder limiter INOP message; we had a SMOKE class II message. We discussed if that was part of the CIDS MEL; as I knew that the smoke detector system was connected to CIDS; but we weren't sure; so we called Maintenance. When the Mechanic returned with the book; we related to him that we had the smoke message and weren't sure if it was related to the CIDS deferral or not; and he attempted a reset. While waiting for the reset; I reviewed the logbook; and saw that the deferral 23-XX-X came from a write up of the Lav Smoke Det System on Date1. This confirmed to me that the SMOKE Class II message was likely related to the deferral. I also noticed that either the Log Deferral sheet or placards had been completed for the New LAV deferral; and prompted the Mechanic to complete those. By then the Class II message had extinguished; and besides the rudder limiter INOP message; no messages were displayed.Upon deplaning in ZZZ; we briefly SMOKE class II message; but by the time we exited the only Class II message was CIDS. After arriving at the overnight hotel; the outbound crew informed us that after some digging and questioning Maintenance Control; it was found that since there was a history of Smoke Det faults; this issue should have been deferred under 23-X-XY; which took the aircraft out of service. We then reviewed the MELs; and what we remembered seeing. Without the knowledge that a history of Smoke Det Faults would require a different deferral; nothing stood out to me to question the deferral. The only time I saw an ECAM for SMOKE DET FAULT was during the reset procedure in ZZZ1; and so was disregarded as part of the reset. Insufficient information available to legitimately question the correctness of the deferral. Late arriving log book prior to departure with multiple issues needed to be corrected. I'm disappointed this event occurred; but without the knowledge that a history of SMOKE DET FAULTS required a different deferral; information that I can't find in the manuals available to me; I'm not sure what I reasonably could have done differently. Regardless; this event has re-emphasized the importance of a thorough review of the maintenance log on every flight.




Synopsis: A321 First Officer reported a misapplied MEL that should have removed the aircraft from service.