Uncovering the mystery of when airlines offer fare sales

Alaska Airlines launched its latest flash sale this past Friday, advertising fares from the West Coast to Florida beginning at $49.

The Seattle-based carrier promoted the deals on Twitter at 6 p.m. PT, with a warning that the sale would end just six hours later, right before midnight.

While some passengers might've jumped at the opportunity to spend some time on the beach for less than $100 round-trip, others were likely offline on Friday night.

So, why exactly did Alaska launch a sale just as the weekend began? Could it have been intentional — something to give the carrier an advantage against its competitors?

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That's certainly possible, according to Marietta Landon, a consultant at Ailevon Pacific. When Alaska filed its $49 fares to Florida, no other airline could match them until roughly a day later, Landon noted in an email to TPG. This way, when flyers searched for flights to the Sunshine State, Alaska's discounted offerings would bubble up to the top of the search engine, when sorting by price.

Contrary to popular opinion, airline fares can't change instantly. (Availability, on the other hand, can change anytime, as explained below.) Landon explained that's due to how airlines must file, or submit, their fares.

Nearly every airline submits its fares to a "clearinghouse" called the Airline Tariff Publishing Company (ATPCO). When passengers search for flights, the engine pings the ATPCO database, which then displays the latest fares.

But despite how many times an airline might want to change a price, it's limited by how often the ATPCO will accept new fares.

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For domestic fares, that's four times a day — at 10 a.m., 1 p.m., 4 p.m. and 8 p.m. ET — between Monday and Friday, and just once a day — at 5 p.m. ET — on Saturdays and Sundays. International fares are accepted hourly, Megan Humphries, head of communications for ATPCO, confirmed to TPG.

So, in Alaska's case, the carrier filed its flash sale at the 8 p.m. ET window on Friday. When other airlines saw — and contemplated matching — there was little they could do. They're limited by the APTCO transmission schedule, which at that point wouldn't have allowed anyone to match until Saturday at 5 p.m. ET – long after Alaska's sale would have come and gone.

In effect, Alaska had capitalized on one of the quirks in airline pricing. By filing Friday night, the carrier put its 6-hour sale out during a window that no competitor could have possibly matched it.

Filing sales at specific times during the week is a strategic move, according to Brett Snyder, founder of the travel service Cranky Concierge and author of the Cranky Flier blog. Like Alaska's late Friday sale, airlines are always looking to get ahead of their competitors. As Snyder describes in an email to TPG, "if an airline filed a sale on Sunday, by the time the others matched on Monday, it would be nearly noon on the East Coast before all the systems were up and running."

But, of course, there are drawbacks to launching sales so late on a Friday or on Sunday afternoon. One of the biggest, according to Landon, is that most people aren't online searching for travel deals on the weekend.

Another is that the revenue management analysts need to actively monitor the availability and progress of a sale. Advertised sales need to have a certain amount of availability; otherwise, the Department of Transporation (DOT) may levy a fine.

Should a sale become incredibly popular, airlines would need to proactively monitor the availability, even on a weekend, or risk possible complaints (and fines) from the DOT.

Despite APTCO not accepting fares for a significant portion of the weekend, airlines still prefer to file sales during the week, according to Landon. In her experience, Southwest typically files its fares in the late afternoon on Mondays. The legacy airlines and ultra-low-cost carriers like Spirit then typically file their sales on Tuesday mornings, Landon says, citing her own observations.

However, the conventional wisdom myth that Tuesdays are the best days to book flights doesn't hold true, since airlines are always changing their timing pattern — like in Alaska's Friday afternoon sale, or in Snyder's experience.

Despite the rigid schedule to file fares, airlines can play with another aspect of the pricing algorithm in real-time: fare-class availability.

When you book a flight, you're effectively taking a seat from the inventory that's assigned a specific fare class, represented by a letter from A to Z. Each individual fare is assigned a particular fare class, so, in general, the higher the fare class, the higher the fare.

Related: What airline fare classes tell you about your ticket

Although fares can only change at regular intervals during the day, an airline could quickly raise prices by "zeroing out" — or closing — some of the cheaper fare classes. Likewise, it could effectively lower the fare by adding seats to previously unavailable fare classes.

As discussed, this is one way for revenue management to ensure that there are enough discounted seats for sale.

ATPCO is completely closed just twice a year, on Christmas Day and on New Year's Day. Landon says that flyers should always be on the lookout for deals around those holidays.

If an airline decided to file a sale before the final transmission on Dec. 24 or Dec. 31, that carrier would have more than a day of uninterrupted competition for its low fares — a move that other airlines might pluck from Alaska's playbook.