(CNN) -- In the interest of "keeping airfares fair," small South Pacific air carrier Samoa Air has started charging passengers by weight.
"We have to take care of every passenger. We have to take into account that not all people are the same shape and size. The bottom line is that airplanes run by weight; they don't run by seats," said Chris Langton, Samoa Air's chief executive.
Samoa Air flies just three aircraft, two 10-seaters and one four-seater, Langton said.
"We're pretty small, but the concept is very big," he said.
The airline serves Samoa, American Samoa, Tonga, Niue, Tokelau, the North Cook Islands and Wallis and Futuna islands in French Polynesia. Langton said the company is planning to purchase a much larger Airbus A320-200 this year for service to international destinations in the region including Australia, New Zealand and Fiji.
"I'm determined to carry this principle through to whatever type of aircraft we operate," Langton said.
Samoa Air's policy went into effect in November. According to the airline's website, "your weight plus your baggage items is what you pay for. Simple."
Samoa Air says its program is the world's first fare structure that charges only by weight.
To book online, travelers enter their approximate weight and that of their luggage and prepay based on that "guesstimate." The airline is not equipped to process payments online, but that service is coming soon, Langton said.
Passengers and their luggage are weighed again at the airport.
And if your weight and that of your bags exceed your booking weight? Langton said the airline has a "fiddle factor" of about 2%. So Samoa Air will let a few kilos slide, but the airline is unlikely to provide a refund if passengers roll up to the tarmac with a lighter load.
Langton said families have been pleased with the pricing model because it often costs less to fly with children using the pay-by-weight model than it would to purchase flat-fare seats.
"People deserve to be able to travel in comfort, and the industry has been trying to fit all the square pegs into round holes and hasn't been taking into account that for a lot of people, traveling by air is an uncomfortable experience," he said.
The idea of charging passengers by weight has been batted around before. A Norwegian economist recently published a paper advocating the practice.
Some travelers have criticized the weight-based fare concept as a "fat tax." Others say they believe it's only fair.
"Yes, if I am getting less than 100% of the seat I paid for, the person taking my space should have to make up the difference," a CNN.com commenter wrote.
Some major U.S. airlines have policies for passengers of size, requiring those who do not fit into a seat comfortably to buy a second seat.
For a tiny carrier like Samoa Air, the fare model seems reasonable, according to airline analyst Vaughn Cordle, a partner at Ionosphere Capital.
"For this small operation, specifically with the aircraft they fly, weight restrictions are the key practical problem they have to deal with on every flight. They have a solid business case to charge for weight," Cordle said.
"The nature of their business model, island-hopping with a small aircraft, they have to do it. The alternative is to charge more on a flat rate, and then everyone is discriminated against. Makes sense to not penalize a lighter-weight passenger. The cost per pound is so high on those light airplanes."
But air travelers are unlikely to see anything like it on a large U.S. airline, he said.
"For U.S. airlines, I think this is an issue they will not touch with a 10-foot pole because of the negative publicity and the practical purposes of weighing people at the gate."