Along with selling meals and charging to check luggage, some airlines have a new product to hawk: insurance.

Northwest Airlines, Continental Airlines and America West Airlines are all now selling insurance against trip cancellations. You'll be offered "Ticket Protector" once you click to buy a nonrefundable ticket from the airline's Web site, or from online travel seller Orbitz Inc. The pitch: Pay an extra 4 percent or more and if you have to cancel, you'll get your money back.

Should you buy it? Only under very limited circumstances. After all, if you read the fine print, you'll see the insurance covers only very limited circumstances.

Fare watcher Terry Trippler points out that it takes a measure of chutzpah for an airline to create severe restrictions like making a ticket nonrefundable, then selling insurance to avoid the effect of its own rules. "It's sort of double-dipping. You set the rules, and then turn around and charge people to escape them," said Mr. Trippler.

Airlines say they are simply offering customers a choice, and note that trip insurance has been sold by others for years. Customers can also avoid nonrefundable ticketing problems by buying more expensive unrestricted tickets, airlines say. "A significant number of our customers find it to be valuable," Continental spokeswoman Julie King says of the insurance.

Continental currently is selling trip insurance written by Access America, part of German insurer Allianz AG, and says it is pleased with the results. So is Northwest, which started offering insurance on nonrefundable tickets in September.

"Sales of our insurance products are meeting our expectations," says Northwest spokesman Kurt Ebenhoch.

Airlines aren't writing insurance themselves, but they are paid by Access America for "advertising" the product to customers. The most-basic form of the airline-offered insurance is far more limited than traditional trip insurance, which often reimburses travelers for medical expenses, hotel cancellation penalties or nonrefundable cruise-ship payments.

The "Airline Ticket Protector" will reimburse you for the cost of your ticket, up to $3,000, if you have to cancel for a "covered reason." It costs 4 percent of the total price -- $40 on a $1,000 ticket. Northwest offers international travelers a more-expensive product at 5.5 percent called "Comprehensive Trip Protector" that includes some medical coverage and emergency medical transport.

With either level, "covered reasons" turn out to be fairly limited. They include sudden medical emergencies, but not all medical emergencies. The insurance doesn't generally cover for you a medical problem already being treated. In other words, if you've had a heart attack in the previous 120 days and want to protect your nonrefundable tickets against another heart attack before departure, don't count on this product. If your doctor has upped your prescription recently, that's a change in condition that'll kill your coverage, according to Access America.

"Ticket Protector" covers you in case of a labor strike at an airline, but you already have some protection there. Airlines honor tickets from competitors in the event of a strike or a shutdown. "Trip Protector" will refund the price of your ticket if your flight is canceled because of a natural disaster or bad weather, too. That's fine if you want your money back. But airlines routinely waive change fees and penalties when bad weather strikes so passengers can rebook trips.

The fine print limits the insurance company's exposure. The insurance also covers traffic accidents, for example, but only if the accident happens on the way to the airport. It covers you if you get scared off by a terrorism incident, but only if the country you're ticketed for gets hit within 30 days before your departure. And countries where there have been terrorism incidents in the previous six months are excluded.

It covers you if your employer terminates you through no fault of your own -- as long as you have been in the job three years or more. And it covers you if fire, flood, vandalism or natural disaster makes your home "uninhabitable."

And here's a particularly ironic condition: The insurance will refund your ticket if jury duty, court order or subpoena requires you to cancel your trip. The irony being that having an upcoming, nonrefundable ticket in your back pocket when called for jury duty can sometimes be helpful when asking the judge for an exclusion from long trials. In other words, the ticket can be some of the best insurance you can get from being placed on a jury.

Access American won't say how often customers actually collect under airline cancellation insurance, but the company does say the most frequent reason is illness or injury.

If you're worried about unexpected illness and have expensive tickets, "Trip Protector" offers some relatively cheap peace of mind. Many don't want to be begging airlines for compassion during a personal crisis.

Of course, the few unforeseen disasters that are covered tend to be the kind of life-crisis situations in which airlines should be granting leniency to their customers anyway. Some do in the face of medical emergencies and other woes, without dinging you for extra protection. They figure helping customers can generate long-term buying loyalty.

What the insurance doesn't cover is simply changing your plans -- that's what most travelers would want.