But wait, let me revise that slightly, thanks to a handy new pay-by-your-weight guide that the little South Pacific airline Samoa Air provides when you book a flight.

Now, if I so decide, I can fly one way from Faleolo Airport in Samoa to Pago Pago in American Samoa (I chose Pago Pago because I like saying it) for 159 Samoan tala, which is about $69.90 That fare comes up after I enter in my weight, 75 kilograms, or 165 pounds. But if I still weighed the same as I did last fall, before I lost 30 pounds on a simple diet, that fare would be 186.56 tala ($79.04).

So hooray for Weight Watchers for saving me 15 percent on a trip I have no intention of taking. Yes, you can reliably reduce your fare, on Samoa Air at least, by reducing your weight. The fare is calculated online based partly on the weight you enter, but the honor system doesn’t apply. As the Samoa Air Web site says, “Don’t worry. We will weigh you again at the airport.”

Let’s not get carried away with this development, though. Samoa Air is but a small island-hopping airline that flies little propeller planes where weight and the distribution of weight have always been considerations. Besides, Samoa and the South Pacific region have obesity rates that are among the world’s highest. By imposing a fare scale based on actual weight, rather than just depending on a pilot’s observations about overall payload, Samoa got a lot of worldwide publicity.

But could charging fares based partly on a passenger’s actual weight be a trend? Not a chance, airline executives say — though they will not publicly discuss competitive fares (antitrust rules frown on it) and especially won’t discuss the touchy subject of fat passengers.

Imagine the chaos of standing in line at a departure gate, waiting to step on a scale along with 150 other passengers (or 550 passengers on a big A380), one by one. On the other hand, weight in general is a serious concern for airlines — the concept of flight being a matter of basic physics. Basic economics also counts, with jet fuel prices at nearly record levels.

Periodically, there are news reports of passengers complaining that grossly overweight passengers encroached on their limited personal space on crowded flights, and should be required to buy an extra seat. Airlines have approached this issue gingerly, given the potential for litigation.

Southwest Airlines, for example, has a carefully worded “Customers of Size” guideline that says in part: “Customers who encroach upon any part of the neighboring seat(s) may proactively purchase the needed number of seats prior to travel” or, failing that, have the option of “discussing their seating needs with the customer service agent at their departure gate.”

All over the world, airlines have been assiduously working to reduce the weight any airplane carries. Some international airlines, for example, are eliminating the heavy hardware and wiring required by elaborate in-flight entertainment systems in favor of individual tablets using Wi-Fi technology. Some have eliminated heavy drink carts and instead require flight attendants to hand-carry trays.

Others have eliminated or reduced the size of airplane galleys, especially given that a hot meal in coach has faded into memory. Some replaced silverware in first class with lighter-weight plastic utensils. In Europe, the scrappy discount carrier Ryanair even reduced the page size of its in-flight magazine. And last year, an executive at Ryanair, which is no slacker itself when it comes to generating publicity, even suggested that flight attendants might consider losing a few pounds in the interest of corporate profitability.

E-mail: jsharkey@nytimes.com

Article source: http://www.nytimes.com/2013/04/09/business/airlines-weigh-costs-and-passenger-pounds-on-the-road.html?partner=rss&emc=rss