Finnair is asking passengers to weigh in before boarding its planes, but it's only for science—and fuel costs and safety.
The airline is hoping to collect data for several thousand passengers to compile more accurate data on what a planeload of passengers and luggage weighs, so they can avoid loading more fuel than is needed, or cutting too close to the edge.
Up to now, they've been using 8-year-old data compiled by the European Aviation Safety Agency. But preliminary checks showed that that data is either dated, or not quite right for Finns, whose average weight turned out a bit higher than the EASA averages.
It's not the first time an airline has done it, and we're not talking about Samoa Air's 2013 attempt to charge fare by the kilo, with fat people or folks with heavy luggage paying more. That airline, by the way, is no longer flying.
But Hawaiian Airlines did a survey similar to Finnair's in 2015, concerned that flights to Pago Pago were using consistently more fuel than expected, which told them that their weight assumptions were probably wrong. Hawaiian has also done similar checks on flights to Korea and to Tokyo Narita.
The other factor is safety: too much fuel adds to the plane's weight, and in hot weather, when air is thinner, that may make it unsafe or impossible for a plane that's too heavy to take off. Last June, 40 flights out of Phoenix were canceled for that reason, and last year Norwegian canceled some Las Vegas service, because heat-related weight limits would have forced them to fly with more empty seats than were profitable.