WEIGH TO GO: Air Samoa believes the new payment policy will help promote health and obesity awareness.

Samoa Air has become the world's first airline to implement "pay as you weigh" flights, meaning overweight passengers pay more for their seats.

"This is the fairest way of travelling," chief executive of Samoa Air, Chris Langton, told ABC Radio. "There are no extra fees in terms of excess baggage or anything – it is just a kilo is a kilo is a kilo."

Like many Pacific island nations, Samoa has a serious obesity problem and is often included in the top 10 countries for obesity levels. As such, Mr Langton believes his airline's new payment policy will also help promote health and obesity awareness.

"When you get into the Pacific, standard weight is substantially higher [than south-east Asia]," he said. "That's a health issue in some areas. [This payment system] has raised the awareness of weight."

Under the new system, Samoa Air passengers must type in their weight and the weight of their baggage into the online booking section of the airline's website. The rates vary depending on the distance flown: from $1 per kilogram on the airline's shortest domestic route to about $4.16 per kilogram for travel between Samoa and American Samoa. Passengers are then weighed again on scales at the airport, to check that they weren't fibbing online.

Samoa Air operates BN2A Islander and Cessna 172 aircraft.

Mr Langton said he believed it to be a system of the future, and added that "the standard width and pitch of seats are changing as people are getting a bit bigger, wider and taller than they were 40 to 50 years ago".

He also pointed out that families travelling with small children could end up paying far less with the pay-by-weight scheme.

"A family of maybe two adults and a couple of mid-sized kids ... can travel at considerably less than what they were being charged before," he said.

Public relations and marketing representative for Samoa Tourism, Peter Sereno, said he believed that the policy would also help with safety standards.

"When you're only fitting eight to 12 people in these aircraft and you've got some bigger Samoans getting on, you do need to weigh them and distribute that weight evenly throughout the aircraft, to make sure everyone's safe," he said. "At the end of the day, I don't care who they're weighing or how they're weighing them as long as it's safe."

Norwegian economist Bharat P. Bhatta proposed in a recent article that by implementing pay-per-kilo policies, carriers could also recoup the cost of the extra fuel required to carry larger people.

Some airlines in the United States already force obese passengers who cannot fit in a single seat to pay for two seats, but this is the first time a per-kilo rate has been used by an airline.