An American airline won the right to weigh its passengers over a six-month period earlier this year to learn how it could save fuel, after discovering the average passenger and carry-on luggage was heavier than expected.

Hawaiian Airlines has now scrapped pre-booked seating for people flying the 2,600-mile route between Honolulu and the American Samoa.

Instead, passengers will be assigned seats when they check-in to make sure weight is evenly distributed around the main cabin of the plane. The airline will keep at least one seat open per row or place children under the age of 13 in those seats.

Some passengers said the policy was discriminatory as it only affects people flying on one route, from Honolulu to Pago Pago, with most passengers being of Samoan descent. Samoans have among the highest rates of obesity in the world.

Six complaints have been filed with the US Department of Transportation since 29 September, as reported by the Economist.

The department ruled in favour of the new policy, with airline officials claiming an even distribution of weight could prevent a crash landing.

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Hawaiian Airlines said it had conducted a voluntary, six-month passenger weight survey on the Pago Pago route, starting in February, asking all passengers to be weighed along with their carry-on luggage.

As a result, the airline scrapped seat pre-selection only on the American Samoa route because the other flight routes surveyed, for example in Korea and Japan, showed no evidence of excess weight.

The airline had also ruled out other possible causes of fuel loss, such as strong winds.

Spokesperson Alex Da Silva told The Independent that no passengers will be asked to step on the scales now that the survey has been completed, and that the airline can still accommodate all parties and can sit families together.

Hawaiian Airlines is not the first passenger carrier to make the move. It follows Samoa Air starting to weigh passengers in 2013.