Understanding Airline Inventory

I’m going to spend this week discussing how to find low-cost airfare options by making use of airline inventory data. Even if you don’t have access to all the different fares available (a service like ExpertFlyer can help you with this) the availability in each fare class or “bucket” is usually enough to at least give you a sense of whether you’re getting the best possible deal.

Let me remind you right off the bat that “fare class” or “booking class” is entirely different from “cabin class.” The cabin class is the class of service you can expect on the plane, whether first, business, coach, or whatever silly name an airline has concocted in recent years. Frequently there will be some correlation. If your fare class is F, then that always means first class. Similarly, Y always means coach or economy class. However, some airlines have rules that allow a Y fare to get an instant upgrade (with conditions) to first or business class, and even lower fare classes can get upgraded during the window for elite upgrades close to departure. There is also a lot of variation in the letters used for discounted fare classes.

I mentioned at the start that fare classes are sometimes referred to as buckets. This can sometimes make them easier to understand. An airline is always trying to get maximum value for its seats, but it has to try to sell them all before departure or they will become worthless forever. Just like a grocery store that puts stuff on sale to get food out the door before it spoils, an airline will sell tickets at a range of prices. (Check FlightAware.com to see the range of prices for your particular flight.) However, unlike a grocery store, those prices seem to go UP as the departure time approaches and they become increasingly close to becoming worthless. Why does this happen?

Lets ignore for a moment that each fare bucket has it’s own fare rules. Instead, imagine that the airline knows in advance roughly how many tickets it will be able to sell at each price. If a plane holds 100 people, it may determine it can sell 105 tickets (assuming 5 no-shows) and it will assign the sale prices in advance. If there are 10 fare buckets, each bucket gets a certain number of available tickets, just like the grocery store assigning each apple a different price based on projected sales and putting them in different buckets. When you go to buy a ticket or an apple, you’re very likely to buy the cheapest one, and as those cheaper tickets/apples disappear, you’re left with more expensive options.

Sometimes overlap exists with the full-fare, unrestricted buckets. So if an airline has 6 first class seats available, it might list 6 tickets in the full-fare F bucket AND 4 seats in the discounted first class A bucket. That doesn’t mean there are 10 seats. Instead, as A tickets are purchased, the number decreases in both the F and A buckets. Similar inventory changes occur with economy tickets as the Y bucket will have many more seats that could alternatively be bought as M, W, or G fares. The unrestricted bucket will always be largest, however the most you’ll ever see at one time is 9. Even if there are 20 seats in a bucket, the counter just stops working at 9.

The breakdown of fare classes looks something like this example from United Airlines. You’ll notice that each cabin class has its own list of fare classes. To understand the hierarchy, just read top to bottom and left to right. An F fare ranks higher than an A fare, and a Z fare ranks higher than a Y fare even though the first is discounted. Normally hierarchy doesn’t matter much unless you’re in an upgrade or standby situation.

United Fare Class chart

But let’s get back to fare rules. Each fare has different rules attached to it that include what days (and sometimes times or months) you’re allowed to travel, how it can be combined with other fares on a multi-leg journey, and a deadline for purchasing it, e.g., three weeks in advance. When you’re researching ticket prices and see a $100 fare one day that doubles to $200 the next, that doesn’t necessarily mean someone bought up all the $100 tickets. It could just mean your $100 ticket is no longer available because you can’t meet the fare rules for the particular day you want to travel. The airline took that bucket of apples and threw it away. It always bothers me when my parents wait until one or two weeks in advance before telling me they’ll be home for a visit because then the price goes up and I can no longer afford it.

Essentially you are fighting against other passengers, who might buy up the cheap seats, and the system, which might decide that those cheap seats are no longer permitted to be sold. There are also small changes in availability performed by the inventory management department at the airline. Why does this make any sense? Why are airlines discounting a perishable product up front rather than waiting until the end when it’s at risk of becoming worthless?

Seats on an airplane are mostly fungible, meaning they can be interchanged without any difference between them. Maybe not the actual seat you sit in, but everyone will get from A to B. Oil, corn, gold, and other commodities are also fungible. Dollar bills are fungible. If you could get that same ticket at the last minute for half price, everyone would wait and there’d be a mad dash at the counter on the day of departure. Unlike an apple, which really does start to decrease in quality every minute it sits on the shelf, the ticket will get you there whether you buy one month in advance or one day. However, the airline knows that as the departure date gets closer, business travelers who are still buying tickets really need to get where they’re going on time. People who buy far in advance are typically leisure travelers who just pick whatever’s cheapest.

Your best bet if you find a fare you like and aren’t ready to buy is to figure out what fare class it uses, the associated rules for how long it will remain available, and how many of those tickets are left so you don’t get left out in the cold.

Identifying the fare class is tricky with online travel agencies (OTAs) like Orbitz or Expedia because they generally don’t share that information with you. Sometimes at the end of the booking process, right before you confirm your purchase, there will be an option to view the rules associated with your ticket. This may include your fare class or at least a one- to six-character fare basis code like “Y” for an unrestricted Y fare or “TW14RT” for a discounted T fare. The first letter often gives you a clue. Another option is to price out your fare using ITA¬†and see if the price matches what you’re given by the OTA. ITA will always tell you the fare class, so if the prices are the same, it’s likely you’re being given the same ticket. Of course, I generally prefer to book with the airline itself if I can get it to price out correctly, and those will give you the fare class, too.

ITA itinerary screenshot

What about determining availability? ExpertFlyer or KVS Tool will help you with that, but your options for getting that information for free are somewhat limited. I know of some options, but I’ll wait to post on that tomorrow after I have a little more time to research them. In the meantime, feel free to email me or post below your favorite free ways to look for fare class availability.

The Halfway to Hawaii Game
Finding Fare Class Availability
  • http://thefrequentmiler.com Frequent Miler

    Great info.n thanks!

  • http://www.extrapackofpeanuts.com Extra Pack of Peanuts

    Thanks for the information. This was very thorough, well thought out, and easily presented. Great job! I’ll definitely be more cognizant of my fare booking class from now on!

  • bwiflyer

    Very informative. Still need to learn a lot.

  • paul

    I use http://www.flightstats.com/go/FlightAvailability/flightAvailability.do for free availability checking (you have to register, which is also free).

    • http://www.travelcodex.com Scottrick

      Ah, I see now. You have to hover with your mouse over each cabin for that information to show up. Thanks for encouraging me to take a second look. It’s not immediately obvious. However, it still seems limited to revenue buckets and no award or upgrade fare classes, which is information you can get from KVS, ExpertFlyer, and United.

  • gikine

    Hi Scott,

    How do I search ITA with different fares? For example, I’m looking for a flight on BA, SFO-LHR in Business, three days later LHR-EDI in economy, nine days later DUB-SFO in Economy Plus.


    • Scottrick

      I’m not sure that you can combine business class and economy class in the same search. But one suggestion is that you do a multi-city search and for each flight you specify the exact fare class you want (fare class, not cabin class). For example, BA uses W for its premium economy product so you would use:

      /f bc=w

      But there are many fare classes for first and economy class, so you would have to specify more than one. For example:

      /f bc=y|bc=b|bc=h

      I think the best approach would be to search for and price each segment separately.

  • MIghty Mouse

    Hi Scott,
    I purchased the last D bucket fare for a flight that is 3 months out from now from SZX-TPE and I still need one more seat on the flight. I am wondering if there is a chance if I wait a bit that the airline, ZH in this case, might swap some C bucket ($$) availability back to D ($) or is that not likely to happen? I’ve got a watch for D on Expert Flyer but perhaps I’m wasting my time?

    Any thoughts?

    MIghty Mouse

    • Mighty Mouse

      Since no one answered my question I thought I would add some info in case it might help someone else. After exactly 2 months, I received an email from Expert Flyer this morning that additional D class opened up. Too late for me as I already purchased a different tix.

  • Reto Weber

    Hi Scott
    i am confused with first class, they have all different codes on united airlines first class for example first A gets me triple miles code Y gets me only singel miles. i need to get 100,000 miles this year to get a miles and more senator card from Lufthansa. i have been looking on the united web site and now most all there fares are P code which only gets singel miles. the last few months i have been getting A fares now they are P why does united do this? concerned star alliance member