Allows to specify more elaborate routing rules for fares, for example:
Permitted transfer airports
Maximum Permitted Mileage (MPM)
Carrier/interlining restrictions
Why?
Provides more control over how fares can be applied, especially when it comes to interlining with other carriers or differentiation between low-cost domestic and full-service international fares, for example.
When?
Technically feasible as soon as we have fares in place.
Ah fare is just that: The price charged for a given itinerary. But whether a fare matches a given itinerary is determined by a combination of “fare rules”. And once specific type of fare rule are routing rules.
To give an example:
Say you have 2 fares from MUC to DEN:
Fare A costs 500 ASD and the routing rules say “no transfers permitted”.
Fare B costs 750 ASD and the routing rules say “transfer via FRA, max 2 transfers permitted”.
With these, the following itineraries would be matched:
MUC-DEN: Fare A
MUC-FRA-DEN: Fare B
MUC-FRA-JFK-DEN: Fare B
MUC-FRA-JFK-DFW-DEN: none (too many transfers)
MUC-JFK-DEN: none (not via FRA)
Other fare rules work the same way. So you might specify that the MPM is at most x times the direct distance (might be relevant due to interlining compensation) or that certain legs must be flown on a specific interlining carrier etc. This can be as simple or as complex as I am willing and able to make it