In general, the average male passenger would end up paying more under this scheme because most men are heavier (and taller) than women. I don't see it happening simply because it will lead to a lot of arguments and ill will. If you think the boarding process is a headache now, wait until they make everyone get on a scale before boarding a plane.

Besides, this plan is too egalitarian. Any airline that implements it will have to introduce a free allowance for elite passengers, who already get free checked luggage. On United, it could be something like this:

Weight exemption for elite passengers who are 18+ years old. Children between 14-17 will receive 75 % of adult allowance and those under 14 will have a prorated allowance of 5 % of adult allowance for each year of age plus a minimum of 5 % for those under 1 year old (i.e. a 13 year old gets 70 % and a two year gets 15 %).

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