Date: 201201
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Night
Aircraft: Regional Jet 700 ER/LR (CRJ700)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Taxi
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Training / Qualification; Other / Unknown; Confusion; Communication Breakdown
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural MEL / CDL
Detector: Person Other Person
When detected: Other Post flight
Result: General Maintenance Action
Contributing factors: Aircraft; Human Factors; MEL; Procedure
Primary problem: Ambiguous

Narrative: On the preceding flight that we flew in the same aircraft; we had an MEL requiring the APU to remain on and running throughout the flight; which we did. En route; the APU auto shutdown due to an overspeed condition. We followed the QRH procedures and landed without incident. I then wrote up the new maintenance problem with the APU and Maintenance came out to the gate to take care of it. We were scheduled to continue with the same aircraft. When I printed out the paperwork for the flight; I was surprised to see the new MEL in addition to the old MEL since the new MEL required the APU to not be operated at all and for the APU inlet door to be secured closed; while the original MEL stated the APU must be running for flight. Furthermore; when we printed out the performance data; the remarks section of the performance data stated the APU must be running. I called Maintenance and told them of my predicament with the contradicting MEL's. I was told that the newest APU MEL supersedes the original one and that everything was good to go!I said if that's the case; then why am I getting this APU must be running remark on the performance data? If the second APU MEL supersedes the first; then why don't they remove the first MEL to avoid confusion? I was then told that since they haven't corrected the first APU MEL; they can't just remove it! They also pointed out that the performance degradation for the extra fuel burned while running the APU for the entire flight was now removed; which it was; so this information along with Maintenance telling me everything was correct ultimately lead me to believe I was legal to depart. Having said that; I was never truly comfortable with the conflicting MEL's and I stated so to Maintenance; but since maintenance is not my field of expertise; I believed what Maintenance was telling me to be valid. I asked my First Officer if he was comfortable with going with the conflicting MEL's and like me he wasn't 100% comfortable; but also felt Maintenance had adequately explained and handled the situation enough for us to continue. We thought that at the time; although we weren't 100% sure the Maintenance people were correct; that the problem was taken care of and we were legal to depart. I was only informed today that our company self disclosed on this issue. From my perspective; at the time of the actual event; I was of the opinion that the problem was taken care of and that we were legal to depart. As for what I learned today of the self-disclosure of the company; apparently they discovered what was done was in error and are taking the steps to rectify the problem. I know the Company and Maintenance expect a certain level of skill; knowledge; and understanding of systems for us pilots to do our jobs to the highest of our abilities. We; as pilots; expect the same from our counterparts in other departments including Maintenance. They typically don't do our job and I don't pretend to be able to do their job. That being said; we sometimes have to rely on their knowledge in areas that I/we are not fluent in and in this case they were wrong. We all can be just a little bit better in what we do and in our knowledge and understanding of systems and interrelated MEL's to hopefully avoid this particular problem in the future.


Second narrative: On our flight we had to have the APU running due to an MEL. In flight after an APU overspeed master warning we had followed QRH procedures and landed with no further issues. The Captain called out Maintenance. When work was done the Captain printed out the release and noticed that MEL 49-14-01 and 49-10-01 were contradicting each other. Furthermore; after printing out the takeoff data we had a remark requiring the APU running. Following more calls to Maintenance and Company we had the explanation from Maintenance that MEL requiring the APU off and door shut; supersedes the previous APU on and running. Because Maintenance did not do corrective action on the first MEL; could not remove it from the paperwork. However; the performance degradation due to the APU running was removed for the flight. Despite neither the Captain nor I were 100% comfortable with the situation; the explanations led us to a conclusion that we were legal to depart.


Synopsis: CRJ700 flight crew reports being dispatched with an MEL for an engine driven generator inoperative and the APU running. The APU fails enroute and the flight lands safely at destination. Maintenance then MEL's the APU and explains the contradicting MEL requirements by stating that the newest APU MEL supersedes the original one and that everything was good to go. The crew accepts this reasoning and departs.