In a very roundabout way, the airlines do charge for weight. They just charge everyone equally. Why they can`t ask individuals. People are so sensitive about their weight that even asking about it can be off-putting much less charging differently.
Still though, an airliner has a weight limit. Everything else that goes onto a plane is weighed and computed before the airliner takes off. But what about the people?
It turns out that the FAA has an answer: you use a pre-set [average" based on gender in your passenger manifest. There are different numbers to use based on how many seats your plane has. The fewer you have the more conservative you have to be.
Folks have been getting heavier on average over the years and this has not escaped the FAA`s notice. On several occasions the weight estimates have been increased.
These estimate increases do have an effect on the industry - more passenger weight (even estimated) means less weight remaining for fuel or for cargo (that is,
luggage). That probably does increase costs but the airlines will pass those costs on to everyone rather than to specifically those who are heavier.
In some cases, airlines do need to charge passengers for a second seat. Safety regulations require that armrests be able to go down, that seatbelts need to be fastened, etc. As with weight restrictions, airlines do their best to navigate around this touchy subject but it does come up.
For very small planes though, we do still need weights of every passenger. There just aren`t enough seats for it to work out on average. Knowing that there are Emily`s out there who can get very angry at the mention, it`s important for pilots to be understanding. That said, pilots also know that taking off over max gross weight is very dangerous. So it`s our job to ask, but we try to ask politely and discreetly.