The line is impressive, almost awe-inspiring. It stretches past the Hudson News stand, past the yogurt shop and City Deli, past the office buildings and the Just Plane Kids stores with the beckoning toys.

It goes by the two soldiers with their combat boots and big guns, and winds around the corner to the observation deck stairs, then spills out to the area holding the ticket counters.

This is the line to go through security at Baltimore-Washington International Airport on a recent Saturday morning. Specifically, the line to go through security for the B concourse used by Southwest.

It seems daunting, almost impossible. Yet there she is, with her brown ponytail and her inexplicable perkiness, wearing the trademark khaki pants, the casual sneakers, the blue polo shirt and the company-issued cardigan, which, on her, somehow gives the impression of the cheerleader wearing her boyfriend's letter sweater.

"Anybody whose flight leaves at 8:20 a.m. or earlier, please follow me!" she chirps, as she gathers a group and moves them to the front of the pack, smiling cheerfully at those she's about to cut in front of.

Yes, this is Southwest Airlines, which is almost blithely flying onward in the aftermath of the terrorist attacks of Sept. 11. No staff layoffs, no major flight cutbacks (the airline recently announced it will trim one percent of its flights, for equipment-related reasons), no dire predictions from company honchos about imminent bankruptcy. Just smiles, and free peanuts, and tremendously corny jokes.

"They have a very successful business model and they stick to it fervently," says David Stempler, president of the Air Travelers Association. "They really know what they're good at, they know what's their style, they know what works, and they don't change it based on changing circumstances."

Not even extraordinary circumstances. In the aftermath of Sept. 11, every other airline at BWI cut back on flights except Southwest. All the major carriers had layoffs -- except Southwest. The trademark 20-minute turnaround, which allows Southwest to get flights out of the gate quickly, and is a key to the company's financial success? Still in place, in spite of increased security measures.

And, as the line suggests, the people are still showing up.

There is a father with his 22-month-old daughter in her stroller, an Amish family in traditional dress, an elderly woman who wants to see her sick brother in Orlando, and assorted men with laptops and women with briefcases.

"I take it because it's cheap, and because it's easy," said Alison Clark of Dartmouth, Mass. She regularly flies Southwest in and out of Providence, R.I., rather than taking another carrier into Boston's Logan Airport. She was flying home via BWI last week.

"You get on the plane, you get off, your luggage is there -- boom! You're done."

Southwest does not have statistics for passenger loads beyond Sept. 30, but for the quarter that ended on that date, planes were flying at 69.1 percent of capacity, compared to 71.6 percent the previous year -- despite widespread wariness about air travel during the last weeks of the most recent quarter.

Employees are proud of that fact. At BWI in the late morning of a recent weekday, lines were almost nonexistent -- nothing at all like the Saturday morning pileup -- and a Southwest employee at one of the security gates seemed baffled by the sight of a photographer taking pictures at that time.

"Don't take them now!" she wailed. "We're busy! We have lines! Don't make it look like we aren't doing okay!"

The airline's style is simple: Offer cheap fares and smile -- a lot. Tell jokes. Be cheerful, perky. There are no meals, just snack food -- in particular peanuts. There are no preselected seat assignments. You board in groups, by number, first come, first served. When you sign up to fly with Southwest, you know what to expect. It doesn't make too many promises, and passengers aren't disappointed -- most of the time.

Sure, the airline has its detractors. Often these are regular business travelers who are less than thrilled that, in this time of economic cutbacks, their companies have decided that low fares are more important than preferred arrival times -- or preferred frequent flier accounts.

But Southwest isn't designed for the business passenger who wants to read his spreadsheets in silence and get a quick breakfast onboard. It's designed for families, for fun seekers, for short-haul weekend travelers who will fly anytime they can get the best fare. At BWI, the ticket counter has been decorated with construction-paper chains made by one employee's Girl Scout troop, and there is a massage stand in the Southwest concourse. Prowl any Southwest terminal, and you're bound to find a good share of kids. Even in these times.

Ivan and Teri Boyer showed up at BWI in the middle of last week with their almost-4-year-old daughter, Claire, and baby Elizabeth to fly Southwest to Providence to introduce Grandma to her new grandchild. Ivan flies Continental routinely for business trips, but when the family traveled together, the decision on what carrier was simple.

"We shopped for fares," Teri says, "but Southwest is more fun to fly. We like open seating. They have good music. They tell jokes and stuff."

Oh, yes -- those jokes. At the boarding gate, in flight, as you leave the plane. Fly Southwest, and you may find yourself in the middle of a plane-wide trivia game. After Sept. 11, though, that is one thing that has changed. A little. Out of respect.

"There are no mandated changes," says Southwest spokeswoman Brandy King. "We just let our employees use their best judgment. . . . [The humor] hasn't stopped, but it may have been toned down a bit."

So on a recent one-hour flight between Buffalo and Baltimore, the flight attendants didn't get on the loudspeaker and tell the one about the monk and the monkey. In fact, they looked a little tired, but not so tired that they couldn't make their traditional fuss over the kids on the plane -- the 8-week-old boy in the first row, the 12-week-old one a few rows back and the 2-year-old who couldn't stop playing with the air phone.

Then they quietly served their peanuts, and Diet Coke, and containers of orange juice. It was business as usual. Almost.

Ivan and Teri Boyer, with daughters Claire and Elizabeth, checking in at BWI to fly Southwest to Providence, R.I.Model planes: Passengers line up for humor and peanuts.