Hope this is the right forum for this question.

I was checking out fares to an upcoming trip, and I decided to look at the SEVEN PAGE rules for my fare. While most of it was absolutely incomprehensible, it got me thinking. Do the rules associated with a ticket relate more to the "fare basis code" or the class of service? And what is the relationship between the two? Do the codes themselves mean anything?

The rules are related to the fare basis code - advance purchase, minimum/maximum stay, day of week/time of day restrictions, nonrefundable or refundable, etc. The booking code, or class of service, is usually the first letter of the fare basis code. There is often more than one fare basis for a given booking code. In addition the fare basis codes often change from week to week, with different sets of rules.

Some of the letters in the code have some meaning - e.g., N or NR at the end usually means nonrefundable. Often there is a number in the code, such as 3, 7 or 14. That often indicates the advance purchase requirement. If there are different fares for different days of the week, there will usually be something in the code that reflects that, but those differ from airline to airline. For example, with two similar fares one might have an "O" and the other a "P", where O means midweek and P means weekend. (Another variation on this is the use of X or D and there are many more.)

Also, if there are multiple airports in a city and the fare basis is valid only from one city, there may be the airport code in the fare basis. For example, a fare restricted to Washington Dulles might have IAD in the fare basis.

Fare basis and the rules have a tight link together. Like stay requirements/ whether a Sat. night stay is required, maximum number of travel days, minimum number of stays, whether there is a fee to change the ticketing dates, whether your fare can be VDB or so. It should be all printed on the rules, and the fare basis code contain info about the rules.

Class of service just talk about the broad picture, and restrictions. Like on United, F means full fare, refundable First Class ticket, while V means highly discounted Economy, which is usually non-refundable, and non-upgradable for international travel, except 1K members w/ SWUs. But the fare rules are actually rules that the agents supposed to follow, when booking your trip, or helping you when you need to change anything on the tickets.

One ticketing carrier, city pair and fare basis code contains one set of fare rules (advance purchase, minimum stay, etc.)

The fare rules for one ticketing carrier, city pair and fare basis code can change over time, but at the moment you purchase a ticket, there is only one set of fare rules.

It is important to note that it is the ticketing carrier, not the operating carrier, that (along with city pair and fare basis code) points to a set of fare rules. For example, UA and US could have wildly different fare rules for the same itinerary using the same physical flights. Same with NW/CO/DL.

One of the attributes of the fare rules is the booking class. The purpose of a booking class is 1) the cabin in which you are confirmed (coach, First, etc.) and 2) availability. In order to buy a ticket, you need availability in the booking class along with meeting the advance purchase requirements, minimum stay, day/time restrictions, and so on.

Actually, class of service doesn't really tell you anything about fare restrictions. Although it is usually the case the F (1st class) fares are refundable, there have been some that are not. And though usually the low fares such as V or W are non-refundable, there are V, W, H and other low fares that are refundable. This often occurs when a major carrier such as UA is matching a fare of a low cost carrier.

I don't mean to be nit-picky or contradictory, but it really is only the fare basis that determines any of the rules and restrictions, not the class of service.