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For the past two days, passengers passing through Helsinki airport may have wondered whether their airline is suffering from weight issues.

At check-in, Finnair staff have been asking them to please step briefly on to a set of weighing scales.

But this isn't a new "thin air" strategy to slim down the cargo.

The airline is surveying customers to check that the estimates it has been using to calculate total weight, fuel and safety are accurate.

"Airlines know what the aircraft weighs, what the check-in luggage weighs, but not what passengers weigh," said Päivyt Tallqvist, communications director at Finnair.

So far, they have found 180 volunteers willing to weigh in, complete with carry-on luggage. They need a total of 2,000 to accurately understand their regular payloads, said Ms Tallqvist.

Until now, Finnair has, like most airlines, been using European Aviation Safety Agency (EASA) passenger standard weight estimates, which put a male's weight at 84.6kg, a female passenger at 66.5kg and the average under-12 at 30.7kg.

But the EASA found those averages hide a range of variables: men travelling first class tend to weigh more than those in economy, while for women the reverse is true. The average hand luggage is 6.1kg, but that average falls significantly in the summer and men carry on heavier items than women.

So Finnair is keen to survey the mix of air travellers specific to their airline.

As well as flying Finns in and out of their home country, the airline offers transfers between Asian and European destinations, and they suspect that the combination of tall Finnish men in winter coats, long-haul travellers from East Asia and daily business travellers around Finland will add up to different set of average outcomes.

Finnair is looking for more volunteers to be weighed over the winter months. Then they'll recommence in the spring, when travellers have stripped down to their lighter season togs.

Image copyright Finnair

One question is whether basing the data on those happy to step up might skew the results.

"That's a question a lot of people have asked," said Ms Tallqvist. But she doesn't think it will pose a problem.

"We found yesterday and today we had people of all shapes and sizes. We had Finnish and Asian customers, we had a variety of male and female and of different sizes."

In recent years, other airlines have begun to look at the variation in passenger weight.

In 2013, Samoa Air controversially became the first airline to charge passengers by the kilo rather than per person.

Travellers hold strong opinions on both sides of the argument whether treating heavier passengers differently is fair. But Finnair says that is certainly not what they are considering.

"That has been a concern that some people have raised," says Ms Tallqvist.

"For us, this has nothing to do with ticket pricing or anything like that."