Originally Posted by MichielR

Good chance the bus will drop you at A-EU-W which is bus gates A7-A10. These are "clean" gates for non-Schengen arrivals. In that case you can just go up the escalators to Z, no security check and no passport control.

If you do get dropped by the bus at B, remember this is Frankfurt so the best is to follow the signs to your gate. If the bus is running the signs will direct you to the bus, if not to the SkyLine train.