Sink nailed the definition, proving he knew what it meant, so I let his definition stand. For clarification a "PID" is a request for a Policy Implementation Date under ALPA's Merger and Fragmentation Policy. If successful ALPA would engage its merger procedures which include the filing of a Single Carrier Petition with the National Mediation Board to have the merging pilots found to be a Single Class or Craft in a Common Transportation System under the Railway Labor Act. With that finding, the groups are merged under US law.

That is just the procedure in a nut shell. Since Sailing isn't defending "ALPA can't" currently, I'll step in and argue his side by saying that the NMB is political and somewhat inconsistent. Getting a Single Carrier Petition won against management's arguments isn't easy. It is easier to win if no one is arguing against you (obviously).