Low-cost airlines as a category continue to lure Corporate America with their siren call of low unrestricted fares, more flights that bypass hubs and new transcontinental routes. Result: More business travelers flew discount carriers in 2004 and will continue to do so next year, according to the Business Travel Coalition.

Although low-cost carriers have successfully swiped market share from the traditional airlines, profits at many budget airlines are now stumbling. Problems plaguing the major carriers-high fuel prices and increased competition in particular-are now similarly eating away at the discount carriers’ bottom line. At press time, ATA Airlines became the first major low-fare carrier to file for Chapter 11 bankruptcy protection. Other low-cost airlines were seeking to acquire parts or even all of ATA, which was operating normally in the interim. Even Independence Air could file for Chapter 11 in January, some analysts predict. Still, the fallout hasn’t affected Richard Branson’s plan to launch low-cost carrier Virgin America in 2005.

One thing is certain: In this era of aviation, only the fittest will survive. Independence Air knows this all too well. But not all discount airlines are created equal-here’s a look at some differentiators of other low-cost carriers:

AirTran

One of the few discount carriers with 2x2 business-class seating (37-inch pitch). Its new B717s feature 100 percent fresh air circulated throughout the cabin, and 85 percent of aisle seats have removable armrests. Free XM satellite radio at every seat by the end of 2004, with more than 100 channels. Taking delivery of new B737-700s, also with business class. Offers gift certificates at 888-327-5878.

ATA

Before filing for Chapter 11 in October, ATA had planned to install business class systemwide by early 2005, with 2x2 leather seats and a price cap of $399 one-way for travel anywhere in the U.S. Also wanted to fly to Europe by summer 2005.

America West

Customers can now use Web check-in at www.americawest.com to print a boarding pass from 24 hours to 90 minutes before their scheduled departure time. Offers gift cards through 800-2-FLY-AWA. Taking delivery of 22 A320s and A319s from 2005-2006.

Frontier

Added new point-to-point routes in 2004 that bypass its Denver hub. Adding pay-per-view movies to its 24-channel, seatback live TV. Hired 121 in-house customer service “scouts” at Denver International to assist passengers in the terminal area and inspire customer loyalty.

JetBlue

Plans to expand fleet by 150 planes and workforce by 18,000 in the next seven years. Wants to launch service to Canada and Mexico and use 100-seat aircraft to enter smaller U.S. markets. Vows never to become a hub-and-spoke carrier. Free wireless hotspots at Long Beach Airport and JFK’s Terminal 6. First to install live TV (up to 36 channels on select aircraft); adding up to 100 channels of XM satellite radio (free) and a video system featuring Fox movies and shows (nominal fee). Seatback
cards illustrate Pilates moves and yoga poses, created in conjunction with Crunch Fitness. Travel gift certificates available at 800-JETBLUE.

Song

Delta’s low-cost spinoff works hard at being “fun.” Awarded free tickets in June to passengers who were nice to each other. Allows passengers to check in via the Web from 24 hours to 30 minutes prior to departure. Personal video monitors at each leather seat, with 24 channels of live satellite TV, pay-per-view movies, digital audio and interactive trivia games. Offers low-carb food selections and an in-flight exercise program developed by fitness guru David Barton. Flight attendants outfitted in uniforms designed by Kate and Andy Spade. The only low-fare service that serves all three New York area airports-JFK, Newark and LaGuardia. Song flights earn Delta SkyMiles.

Southwest

Low-fare pioneer has nearly 400 B737s on order through 2012 and could conceivably expand by 30 percent a year. As oil prices have soared, Southwest has saved millions of dollars by hedging fuel, allowing it to rack up record profits while rivals drown in red ink. Consistently scores best on-time record, best baggage handling and fewest customer complaints.

Spirit

Business-class 2x2 leather seating with 36-inch pitch. Online check-in up to 12 hours prior to departing flight. Replacing MD-80s with 35 new A319s and A321s, with an option to buy 50 more. This largest privately held airline also serves the Caribbean and Mexico. Along with Ted, offers no transcontinental flights, unlike all other low-cost carriers listed here.

Ted

As the low-cost arm of United Airlines, passengers earn Mileage Plus miles on all Ted flights. No premium cabins, but 40 percent of seats are Economy Plus (35-inch pitch). Testing a system that allows passengers to rent a DVD player in Denver and choose from among 12 DVD titles. Free in-flight NBC programming and 12 music channels. The only low-cost carrier mentioned here (besides Spirit) that does not offer transcontinental service.

--Karen Goodwin