was implemented in 2013 by Samoa air. Can't tell if it is still in use.
Samoa Air Charges Passengers By Weight: 'The Fairest Way To Travel', Says Chief Executive
Pay as you weigh': Airline to charge passengers based on body weight
Airfares based on passenger weight won't fly, experts say
Samoa Air prices tickets based on passengers’ weight
(Samoa is the most overweight country in the world)
Airlines Weigh The Pounds