To what end ?

Are you saying they can demand arbitration if they disagree with the arbitrators final SLI ?

Is that part of the M-B process ?

If course not.

USAPA not only negotiated the MOU, but they agreed to its provisions by signing it. ALL of the provisions, not just the timeline or the order of occurrence. They cannot cherry pick what aspects within they like and toss that which they don't, although that appears exactly what they demand to do. From a legal position, they own the MOU in its entirety. They want to hold the JCBA portion hostage so they can remain relevant throughout the entire SLI process. Even if for some reason the other parties allow an arbitration to rule on the protocol disagreements, that doesn't (and shouldn't) allow USAPA rights the MOU doesn't support or what they agreed otherwise.

So, if for some reason protocol is resolved, negotiations can then fail if APA isn't willing to support USAPA's hijacking of the US Airways pilots representation by doing to the west what they don't want APA to do to them (make them disappear) and we end up back to arbitration for the final SLI. The only difference is the MOU will be followed, the JCBA will be completed first, almost certainly a STS will be declared and USAPA will disappear like a fart in the wind prior to final arbitration and we are then back to where we would be anyway, that being APA representing all pilots and the only labor party directly interacting with the arbitrators and deciding what is submitted for their consideration, this last aspect being where their DFR duty exists and the crux of their jeopardy.