Experts say that travelers should book while the booking is good. “You’re going to have less availability to choose from. Any of these lower fares or special fares that you see offered are capacity controlled,” warns Janet Stevens of AAA Travel Services.It all comes down to the numbers: there are simply fewer passengers flying these days. In fact, this year’s fourth quarter low is expected to be nearly as low as the record set following the September 11 attack in 2001.

Fewer passengers translates to fewer flights offered. And when the holidays sneak up on travelers as they always seem to do, without as many flights available, there won’t be as many choices left.

So how early do we need to buy? Experts say that anytime between now and the end of October is ideal. “Bottom line is that holiday air travel procrastinators do so at their own peril this year and practical travelers should be shopping now,” says Farecompare.com’s Rick Seaney.

According to Stevens, Thanksgiving morning departures can often help people save money, as well as flying outside normal peak periods. This entails flying a few days earlier–such the Monday or Tuesday before Thanksgiving rather than the day before.

Fewer passengers flying does have its advantages. Processing times should be shorter, and lines should be as well. Flights may not be as crowded, and may be more likely to arrive on time.