Date: 202109
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Dawn
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
ATC / advisory: Ground ZZZ
Aircraft component: MCP
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Time Pressure; Communication Breakdown; Confusion; Situational Awareness
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural MEL / CDL
When detected: Aircraft In Service At Gate
Result: Flight Crew Became Reoriented; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Human Factors; MEL; Aircraft
Primary problem: Human Factors

Narrative: When accepting the aircraft in the morning I noticed that the First Officer's (FO) MCDU (Multi-function Control and Display Unit) was deferred for LSK 6R not working. It was deferred under MEL XX-YY-2; which allows for MCDU 1 specifically to be inoperative. When I read the MEL I was confused about whether the FO's MCDU could be deferred under this MEL since it specifically mentions MCDU 1 being able to be deferred but not MCDU 2. Operational factors and pressure to depart on time got me distracted and I did not think about it again until later in the evening after having completed the day and was on the overnight. I believe the MEL was improperly applied in this situation and because of that the aircraft may not have been airworthy. Since I wasn't involved in the actual deferral I don't know what operational factors could have contributed to this. Proper execution of the MEL by maintenance control could have solved it as the MEL has provisions for the FO's MCDU not working involving swapping the units. Additionally; a call for clarification to maintenance control by myself in the morning when I realized it may be a problem would have helped to clarify any confusion about the MEL and could have gotten Maintenance involved with correcting the deferral.


Second narrative: When accepting the aircraft in the morning I noticed that the First Officer's (FO) MCDU was deferred for LSK R6 not working. It was deferred under MEL XX-YY-2 which allows for MCDU 1 specifically to be inoperative. When I read the MEL I was confused about weather the FO's MCDU could be deferred under this MEL since it specifically mentions MCDU 1 being able to be deferred but not MCDU 2. Operational factors and pressure to depart on time caused a distraction and we did not think about it again until later in the evening after having completed the day and was on the overnight.I believe the MEL was improperly applied in this situation and because of that that aircraft may not have been airworthy. Since I wasn't involved in the actual deferral I don't know what operational factors could have contributed to this.Proper execution of the MEL by maintenance control could have solved it as the MEL has provisions for the FO's MCDU not working involving swapping the units. Additionally a call for clarification to maintenance control by the Captain in the morning when realized. It may be a problem that would have been helped by clarifying the confusion about the MEL and could have gotten maintenance involved with correcting the deferral.


Synopsis: Flight Crew reported discovering that the wrong MCDU was placed on MEL and the aircraft was possibly not airworthy for the flight.