A Y fare is the highest coach fare you can purchase often sold for last seat availability. It is fully refundable and fully changeable without penalty as long as the routing stays the same. B fares have a few restrictions that may or may not have change fees. It all depends on the city pair. I have seen fully refundable H fares on UA that were set in order to compete with WN on certain routes they were priced exactly the same as a BS fare or AT fare. Perhaps you should study the fare rules before posting.