According to Makoto Watanabe, the cheapest time to book your flight, all else being equal, is about eight weeks before you plan to leave.

It's a good one-step rule. But what else should you take into account when trying to get a great deal on an expensive flight? The Wall Street Journal's Scott McCartney has some suggestions.

Bottom line: if you buy your tickets midweek (i.e., Tuesday, Wednesday, or Thursday), you can save a bundle. One expert, FareCompare.com's Rick Seaney, has even pinpointed an ideal time to buy: 3pm EST on Tuesday. So why do fares work this way, anyway?

Though prices fluctuate frequently and the ups and downs of airline prices can frustrate and anger consumers, airline pricing actually does follow a cycle during the week. Many sales, in which some seats are discounted by 15% to 25% typically, are launched Monday night....

When airlines want to push through a fare increase, marking up their basic prices across the board usually by $5 or $10, they often do that on Thursday night, then watch to see if competitors match and if the higher rates stick over the weekend. If competitors balk, prices can be rolled back by Monday morning.

In addition, airlines don't manage their inventory as actively on weekends, so if cheap seats sell on some flights, prices automatically jump higher. Fare analysts may decide later to offer more seats at cheaper prices, but not until they come back to work on Monday, according to airline pricing executives.

The upshot of all this, is that the same ticket can be "$199 certain days and $499 other days, even months ahead of a flight."

This article raises as many questions than it answers. Do corporate travel departments take advantage of airline pricing fluctuations and buy most of their tickets mid-week? How is the development of ever-more sophisticated fare comparison engines, such as Kayak.com, influencing pricing strategies? But this definitely seems like a situation where  the observer effect comes into play. Can journalists and the public extensively study airline pricing strategies without forcing airlines to respond and adjust?

I follow JetBlue's Twitter account for last-minute sales, but I've never bought any of their " cheeps."