Fares on an airline ticket are identified by a fare basis code, such as Y26 in an example IATA gives. IATA’s data standards attach the code to each fare component, the part of a journey priced by one fare, and identify a published fare by its origin and destination, the airline that owns it and its fare basis code. The e-ticket shows the fare basis for each flight coupon, and IATA says the booking class is usually determined by the fare basis.

Airlines write their own codes

Formats vary from airline to airline. Delta limits its codes to eight characters and, in almost all markets, uses the second-to-last character to show the fare brand. It also marks its refundable fares with set characters in set positions. Qantas structures its most common Australian domestic codes as fare class, then fare family, then a condition such as high or low season.

The first letter does not always match the class booked. Delta sells its Delta Comfort fares in W or S class, but their fare basis begins with a Delta Main letter, and both classes must have seats for the fare to be sold.

Worth knowing

• Fares can share a class. When Air Canada changed how it filed its domestic fare families in September 2017, some began sharing booking classes, so the last two letters of the fare basis identified the family instead.

• The code is not the rules. It can hint at conditions such as refundability or season, but the full conditions are in the fare rules.

• Designators. IATA’s standards hold a ticket designator, shown after a slash, separately from the fare basis. Delta uses designators for discount programmes.

• Sales conditions. IATA defines a tour basing fare as one that may be used only for air transport as part of an inclusive tour.