Some steep discounts are available to air travelers in the next two days in what one industry analyst calls "the first big summer fare sale" of the year.

AirTran sparked the sale this week, with US Airways, United, Delta and American among the airlines following close behind, says Tom Parsons, founder of Bestfares.com who tracks ticket prices and scouted the bargains.

But travelers will have to act fast. Tickets have to be purchased by midnight Thursday for travel through Nov. 16. There are blackout dates around Memorial Day and other holidays. And travelers may have to do some digging to find the lowest fares, particularly in July, or when flying cross-country, Parsons says.

"If you're flying coast to coast, you're still going to have to look hard," he says. "The inventory may be restricted in the summer, so you may have a little bit tougher time. The airlines are not going to give away every single seat at a cheap price. But this is the first big summer sale we've had, so there should still be plenty of room."

Travelers might need to make a connection or travel to a smaller, alternative airport to get the lowest fares. For instance, a round-trip ticket on Delta from Orlando to Chicago Midway in May, with a stopover in Atlanta, was priced at $158, minus fees and taxes, as of Tuesday afternoon.

But there were also some non-stop bargains. A round trip in July from Dallas to New York City on American had a base fare of $174, Parsons says.