Date: 201501
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: Marginal
Weather elements / visibility: Turbulence; Icing
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Airspace: Class A ZZZ; Class B ZZZ
ATC / advisory: Center ZZZ; Ramp ZZZ
Aircraft component: Rudder Control System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Distraction; Workload; Troubleshooting
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural MEL / CDL
Detector: Person Flight Crew
When detected: In-flight; Taxi
Result: General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Company Policy; Procedure; Aircraft
Primary problem: Aircraft

Narrative: Before departing; release had MEL for Yaw Trim Indicator being Inoperative Captain (CA) read MEL to me and said to verify trim was set to neutral or '0' before every takeoff which we did verify prior to departure. Ended up three hours delayed due to not having an alternate on our release when we required it; thus not having fuel for the alternate. Ended up 2+ hours delayed due to waiting for fuel and unloading bags after passengers decided to deboard and then pretty much starting from the beginning paperwork wise. Ended up departing finally. Takeoff was normal; noted on climb aircraft required slightly more than normal left rudder trim when I looked at how coordinated the aircraft was flying. Added trim to center the 'ball'; engaged AP and away we went on the flight. Ended up doing an ILS app into our destination thus did not land the aircraft due to it being a CA approach so I was not able to feel what the aircraft felt like when landing. Landed and again; repeated the MEL procedure before departing. Before our first departure noted the Rudder Trim was 1/2 deflected when trimmed during climb and cruise. During descent; we noted aircraft required even more trim to have the ball centered; up to 3/4 of total trim being used to fly coordinated. Noted indicator was working properly if we were able to fly coordinated by applying the correct amount of trim in and in what the normal direction would be if it had been operative. After landing on the next leg; we took all trim out to neutral while taxing and the aircraft pulled to one side.Looking back at the situation; if I had seen how much rudder trim was in; I could've noted something didn't added up. Also; we then noted that in cruise and in the descent into ZZZ; when the aircraft had been trimmed out to perfectly centered; the rudder pedals too were displaced correctly thus verifying that the Yaw trim indication was correct if what showed matched with what the rudders were doing. When we arrived at the gate; I discussed with the CA if that MEL was correct since the indicator seemed to work but the aircraft was still flying uncoordinated and required huge amounts of trim. After we realized how much trim was needed to fly coordinated; we figured it would be very hard to maintain control of aircraft in the possibility of an engine failure with less rudder available with all that trim set during flight; possibly leading to control issues in that scenario. Called Maintenance to verify MEL and they had agreed that the MEL didn't match up. Aircraft ended up being taken out of service due to not being able to figure out what the main problem could be. The MEL wording for Yaw Trim indication was vague when CA read procedure to me. Didn't specify how exactly to verify Rudder Trim was to be set to neutral. Also; with the delays and the huge mess that morning it could've led to just skimming over the MEL. I could've also checked the can but was task saturated with being on the radio with Ops; Clearance; Dispatch and the communicating with the gate agent about the status of the flight. That A/C can had at least three write ups for the same problem and all the corrective actions said were that a flight control test had been done to correct it. Initially; when brought up to Maintenances' attention; there was a disconnect between us as to why this was such a huge problem until it took us a few attempts to explain why this could be a huge issue. Although it didn't present any flight control issues during our normal flights; engine failures can happen (one happened recently here) and could have turned an Incorrect MEL procedure error into a bigger issue had something worse happened. Many of these MEL issues not corresponding to the correct write up stem from Maintenance trying to find a MEL to attach it to thus solving the problem and getting the aircraft out with minima l delay. Sometimes; not a whole lot of reading is done to ensure the MEL being used agrees with what is trying to beMEL'd. We could use quality control in the Maintenance department. to prevent these issues from happening over and over again. Aircraft looked normal and I did not see any visible damage on the aircraft during my walk around that would suggest that there was some bigger issue with the plane causing it to fly that un-coordinated in flight.


Second narrative: [Report narrative contained no additional information].


Synopsis: An ERJ-175 rudder trim indication was MELed; but the crew discovered after flying two legs that substantial left trim was needed for coordinated flight. Maintenance removed the aircraft from service.