[danaris]

There's a big difference between using a mean weight for the correct category of people—which, by definition, will on average be correct, though you might occasionally get enough very overweight people to make it slightly off—and using a mean weight for the wrong category entirely, and thus ending up systematically skewing your calculations.

Just to pull some numbers out of, ah, thin air for an example, if you were using 110lbs as the average weight of a child and 160lbs as the average weight of an adult woman, your airplane seats about 200, and roughly one-third of your passengers are adult women, half of whom use "miss" as their title, that works out to 50 lbs difference * ~30 passengers = 1500lbs.

That's gonna make a big difference.

[b112]

I guess. I just envision a random scenario where a league of... overweight women, are all on the same flight.

This seems to be in the UK, so what if an all female travel group, from the US, for the portly, showed up? When I visited the US, there seemed to be an inordinate amount of people in scooters that were quite.. large.

At least, this is what was in my head.

Then again, I just realised... do they have to buy two seats? Maybe I'm over analyzing all of this.

[danaris]

To the best of my knowledge, there's no systematic requirement for very overweight people to buy multiple seats—though I recall hearing a couple of such people note that they tended to do so for their own comfort.

I would also point out, though, that it's just as likely that there would be something like a gymnastics or other sports team on a plane, which I think should be somewhat under the average weight (despite the extra muscle mass).