Originally Posted by PotatoChip

Essentially it's just a separate pay scale from the current one. It's almost always a lower pay scale based on differentiating factors (i.e. Pilots hired after xxx date will paid this.) It could be all new hires on a new a/c that isn't under the current CBA get paid x new rate, or it could be an airline opens new bases and offers them under a B-Scale.

Again, it's just an airlines way of providing a different pay scale with (A) being the current model.