On many reworked airline sites, for example, customers can easily manage their frequent-flier accounts; travel awards and upgrades, which typically used to be arranged over the phone with an airline clerk, now can be easily booked online. Some sites display calendars showing open dates and seat-availability charts.

As international travel grows, airlines have also simplified the process of booking complicated schedules to just a few clicks — including travel with two airlines that are code-sharing partners.

Many travelers are also drawn to online check-in, which permits passengers to print out their boarding passes and is now a standard feature at airline Web sites. The sites give airlines the ability to promote special fares and other offers through direct marketing and e-mail alerts.

Many of the airlines' Web site initiatives are aimed at increasing, or regaining, business travelers' loyalty.

"Business travelers in general are people who are self-motivated," said Travis Christ, the vice president of marketing for US Airways. "They know what they want and where they want to go. The trick is to improve the level of empowerment available to them online."

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