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It is only a matter of time before airlines start demanding overweight passengers pay for two seats, an aviation commentator says.
Peter Clark said the number of "very large" people boarding aircraft was increasing and people who struggled to get into one seat should pay the extra cost.
His comments follow reports that Air France-KLM planned to make overweight passengers pay for a second seat.
The airline denies it would make obese passengers pay more and says the only recent change is that they will refund the cost of the second seat, if one is bought, if the economy cabin is not full.
The extra seat came with a 25% discount.
Mr Clark said airlines would have to soon start asking bigger passengers to either pay for another seat or take a bigger one in premium economy or business class.
"The airlines will have to take a strong stand on it ... Something will have to happen. It's the responsibility of the passenger, not the airline."
He said airlines would probably try to form a consensus on the issue.
Mr Clark said there were a number of safety issues that accompanied having very large people in planes - like moving quickly in an emergency or something as simple as putting a seatbelt on.
"A large person can create problems if they impede the movement of other passengers or if they have to evacuate [the aircraft] quickly."
The comfort of other passengers was also a concern.
"It's a confined space and if someone is impinging on the space of another passenger - who has paid a lot of money for it - then that's not fair," he said.
He thought there would be "human rights issues" if airlines did ask obese passengers to pay more, but safety concerns should come first.
Air New Zealand expects passengers who know they require additional room to buy an additional seat to get the space they require.
- Andrew Koubaridis of The NZ Herald