Yesterday I encountered what seemed like a pretty strange phenomenon. There was a roundtrip United fare between Chicago and London for under $600.

Searching for availability using the ITA Matrix (the publicly available airfare search site from ITA Software, owned by Google) the fare appeared to be available only for Saturday departures:

However searching metasearch site Momondo I was coming up with the fare most days during the months it’s available (and for a bit less money).

This seemed like an odd result, but The Flight Deal offered that it seemed to be an ITA glitch. ITA does a great job searching published inventory and constructing fares, but it isn’t perfect. They noted if you specified the specific fare you’re looking for ITA would come up with it on other dates. And so it is:

I knew from my earlier post what the fare basis was: KLNC14NS

Here’s the instructions I gave to ITA:

See, I told ITA to look for flights across a full month where that specific fare was available. ITA is great, what it’s doing in this case is automating something that used to be a hard manual process for frequent flyers.

It begins by searching fares. I like Expert Flyer for that.

Here’s the cheapest United fares between Chicago and London:

Once you find the fare you want, what you’d do is read the fare rules.

• What range of dates is the fare available, e.g. January – March
  
• Are there certain days of the week that you can fly, e.g. Tuesday/Wednesday only
  
• How many days advance purchase is required?
  
• Are there specific flights the fare is valid for, or specific flights that aren’t permitted?

Then take note of the fare basis. The first letter will usually designate the ‘inventory’ you’re looking for. This is a K fare, so you need flights where there are K seats available.

I pull up February 1 and find that all 3 United non-stops have K seats available. Therefore I should be able to use any of these flights towards an itinerary at this fare (since the fare is also available in February without day of week restrictions).

Now, this all can get more complicated especially with international itineraries that involve more than one airline, such as when you’re flying to a destination that the airline whose fare it is doesn’t serve. You get into questions of which airlines you can fly for those other segments, and which you cannot, and then have to look for their corresponding inventory also.

That’s one of the things that makes ITA so good, although you do sometimes have to feed it information rather than asking it to do the fully automated job that I sometimes fall into the trap of.

ITA doesn’t sell you the tickets you find, you have to book them yourself, but one convenient little shortcut is this site that helps you book what you find there.

Oh, I should point out another hiccup. Sometimes all of these sites don’t play nicely or give you the results you want. When I pulled up that list of fares, there was an even cheaper one — $119 base fare versus the $182 that gave me $597 tickets. Remember I was finding cheaper fares on travel booking sites through Momondo as well.

I specified that fare basis into ITA Matrix and the fare came up, $59.50 each direction. But the tickets were pricing higher, because of $518 fuel surcharges versus $200 fuel surcharges with the other discount fare.

So… it’s back to Momondo. And back to consult my dog-eared 5 year old copy of Nicholas Kralev’s Decoding Air Travel which explained all of this.