It's becoming an annual sign of fall: Kids go back to school, afternoon temperatures become slightly less suffocating and the nation's airlines

announce a fare sale.

This fall's version - similar to but about a week earlier than those of previous years - offers discounts of up to 50 percent off regular fares. Tickets must be purchased by Friday and travel must be completed by Dec. 15.Most of the discounts include tickets to and from Orlando, which often is excluded from fare sales because of its popularity. Because markets are discounted at different rates, tickets to some areas, like the West Coast, are deeply reduced while others, like Chicago, aren't much cheaper than regular full fares.

Still, the current sale involves discounts to more markets than usual, said Bob Ente, president of Sunniland Travel in Orlando and area director for the American Society of Travel Agents.

''The general consensus is that this is a real sale," he said. "There are more markets involved and there's been some good matching. If you know you're going to be going somewhere, this may be the time to buy."

The sale was launched late Sunday, with Continental Airlines offering smaller discounts and fewer restrictions and Northwest Airlines offering deeper discounts but more restrictions, said Bob Parsons, editor of Best Fares Discount Travel Magazine of Arlington, Texas.

On Tuesday, the nation's other major carriers matched Northwest's fares and Continental's looser restrictions.

"It's putting the consumer in a win-win situation," said Kelly Whitley, Best Fares spokeswoman.

Restrictions vary, with many carriers offering their best discounts to travelers who buy nonrefundable tickets at least seven days in advance, travel Monday afternoon through Thursday morning or any time Saturday, and extend their trip over a Friday or Saturday night.

In many cases, the discounts also are available over Thanksgiving weekend - as long as consumers don't travel the Wednesday before the holiday or the Sunday afterward.

The price cuts are painful for the airlines, despite improved profitability, because of a looming threat of a higher jet-fuel tax. But they attract so much business that they're impossible to ignore, airline representatives said.

"This business is so competitive that everyone matches or you lose market share," said Tim Smith, a spokesman for American Airlines in Dallas. "There is always that certain amount of people who stand on the sidelines until something like this catches their eye."