The latest information comes from the online travel agency, CheapAir.com, focused on how far in advance the optimum time to buy might be. CheapAir's data are based on extensive mining of its own purchase records:
-- The report also notes that you find lots of deviations from this average. CheapAir found some routes where the best time to buy was when the flight first opened, 331 days in advance, and others when the cheapest tickets were last-minute. And, of course, you're better off buying earlier for travel around major holidays.
-- The report's data dispute the urban legend about buying tickets on Tuesday and Wednesday: CheapAir found little day-to-day difference.
Two online outfits -- Bing Travel and most recently Kayak -- boast a different approach: "buy or wait a week" airfare predictors on their search engines. I'm currently testing them and will report results soon.
Beyond trying to pick the best periods to buy, you have the option of tracking fares and the possibility of getting a refund if a fare drops after you buy. CheapAir has what appears to be the one of the best such programs: "Price Drop Payback" promises that if you buy a ticket through CheapAir and the fare subsequently goes down, the agency will issue a credit in the amount of the difference, up to a maximum of $100. The deal applies only to online purchases of nonrefundable economy-class tickets, and only to fare drops posted on CheapAir for the exact same itinerary.
Other big OTAs provide somewhat similar programs. Orbitz offers a credit up to 110 percent of the difference, but only if someone else actually books the identical itinerary on Orbitz. Expedia offers a guarantee, but only for price drops that occur within 24 hours of purchase.
Another approach is to request an alert whenever a fare drops on some route you want to fly. Here, you have lots of options: Most big OTAs offer such a service, some airlines offer it, and some independent third-party travel information sites, including SmarterTravel.com, the source that posts my columns. Most third-party agencies do not include Allegiant and Southwest, two lines that block "screen scraping" by external agencies, but George Hobica's human-powered AirfareWatchdog.com does cover these lines. You enter one or more routes and your email address and the source notifies you of a fare drop. These days, some of them also provide smartphone and iPad apps.
All in all, you won't find a single magic bullet answer to the when-to-buy question. Instead, your best protection is to avail yourself of a number of different approaches and keep on top of the airfare marketplace.
(Send e-mail to Ed Perkins at eperkins(at)mind.net. Perkins' new book for small business and independent professionals, "Business Travel When It's Your Money," is now available through http://www.mybusinesstravel.com or http://www.amazon.com)