You've seen the latest barrage of ads from Piedmont Airlines, I'm sure -- the ones that are headed: IF YOU WANT TO FLY FIRST CLASS, THIS COULD BE JUST THE TICKET.

Right under the head comes the math: For trips of 500 miles or less, a first-class ticket will cost you only $20 more than full-fare coach. For trips between 501 and 1,000 miles, $40 more gets you into first class. For trips of 1,001 miles or more, $60 is the surcharge.

The catch (isn't there always one?) is the phrase "full-fare coach."

The last person who paid full-fare coach was your maiden aunt Tessie, because she was the only person on earth who didn't know about Super Savers, excursion fares and all their cousins. The rest of us learned long ago that you can save serious dough if you fly steerage and plan your trips a little farther ahead than you used to.

Mary Robinson of Potomac flies to and from Lexington, Ky., on Piedmont twice a year. The fare she's used to paying is $208 roundtrip. That happens to be discount coach.

But Mary didn't realize that. She thought $208 was Tessie Fare. She also believed Piedmont's ads, and thought she could fly to Lexington in a sea of champagne for only $20 or $40 extra each way.

So when she called Piedmont to verify the roundtrip first-class fare between Washington and Lexington, she nearly choked. "That would be $522," the ticket agent said -- or $314 more than Mary's usual.

Mary couldn't help asking the agent what $314 extra would buy you on a pair of one-hour flights.

"You would fly more luxuriously," the agent replied.

Asked to explain that, Don McGuire, Piedmont's vice president for public relations, said that first-class Piedmont luxury includes "more room, free beverage service, and a more personalized service, with one attendant per eight or 10 people, rather than one attendant for as many as 60 . . . . If your first concern is the lavishness of the service, that's the saving."

No offense, Don, but may I ask Tessie a question?

Do a free scotch, a seat that's two inches wider and a quicker copy of Popular Mechanics sound as if they're worth $314 to you?

Me, neither.

A little unfinished business, under the heading of fires:

Back in September, I recounted the story of a car that caught on fire in the RFK Stadium parking lot, just as a Redskins crowd was starting to go home. Somehow, Engine Company 8 of the D.C. Fire Department battled its way into the jammed lot and put out the fire. Heck of a job under very trying circumstances, I wrote.

A number of readers agreed, but noted that Engine 8's performance had been much ado about nothing.

"A simple box of baking soda in the glove box would have put the fire out," wrote John A. Moody of Northwest (and, similarly, many others). "Cheap, easy and effective. More people should know of this."

Asked to comment, Leon Givs, a fire department spokesman, vigorously disagreed.

"A person should remove themselves from the area and not make any attempt to handle the fire," said Leon. "We have a special foam for fighting engine compartment fires. I can't emphasize to you enough that special skills and equipment are needed for these kinds of fires and people should let the fire department fight them."

John's method would be fine for a match that falls into a kitchen trash can. But if a car engine is afire, let the pros handle it.

Amen Corner:

Colleen M. McEvoy of Woodley Park says she agrees with a correspondent of mine who decried the way Washingtonians snort and snuffle in public.

Colleen says there's a far worse problem:

Gum.

She says she sees local folk "expectorate it onto one of D.C.'s beautiful streets or place it in a host's crystal ash tray, under a table, chair, Metro or bus seat or bedpost . . . .

"Soon we can rename Pennsylvania 'Gum Avenue,' Dupont 'Gum Circle,' and so on."

I suppose I could encourage readers to use trash cans, Colleen. But you know how much good that would do.

I suppose I could remind readers that, in a month, Santa Claus will know if they've been naughty or nice. But, yes, Colleen, only Virginia believes in Santa.

So I will offer up Levey's Law of Thermogumular Dynamics: If you toss your gum around, you will sooner or later step in someone else's. May it ruin your good shoes, dear sir or madam, as you have ruined the shoes of the rest of us.