To maximize profits, let's set the base price on a passenger weighing 99 lbs, US Customary Units. All others pay $1.23 / additional pound (funny number includes taxes, fees, etc.) There will be a scale installed in floor at the bording area. As you board the plane, any passenger weighing more than 99 lbs. will need to swipe their credit card to pay the additional fare. (I'm joking about this plan)