Originally Posted by
anabolism
What does "A required when available" mean? If the flight sells A, then book into A? I'm trying to understand this line in the context of following the two route-specific exceptions.
You read the table from the top down, stopping when a rule applies.
"A REQUIRED WHEN AVAILABLE" means that if the flight has A class and has space in A class, then the fare must be booked into A class (unless a rule further up the table already took precedence). If the flight has no A class, or if A is 0, then you can continue down the table.
If you wanted to restrict it book into A if A is ever sold on the flight, and not allow the passenger to downgrade into a different bucket if A is full, the wording is "A REQUIRED WHEN OFFERED".
[This is actually a human-readable interpretation of a set of logic rules. The computer doesn't read the table exactly when it wants to book a passenger into a bucket, but it gets the information from the same place as the table is constructed.]
By the way, I actually dug out the ATPCO documentation that describes the format of this table. The document is literally 272 pages long: just for the RBD table, just to describe the data format for allowing a fare to define which classes it books into. So don't feel too bad that it isn't obvious how it works.
