Pay as you weigh fare

I think it's a problem on those really small twin-prop planes. I've seen people have to be offloaded from those flights because they were over the legal take-off weight. Sometimes, I'm sorry to say, the situation dictates it. I've had to provide my weight details before when getting on small charter flights.

As I understand it, the airlines estimate the average passenger is 80kg (~176 lbs). And while that may have been a valid assumption to make 20 years ago, I dare say that it's a gross underestimation these days.

Seems fair to me. How much weight is on a plane matters, same as you have to pay extra for more luggage.
That being said, for people who are THAT big they probably already have to pay extra in the form of two seats anyway?

I've been on an Air Pacific flight to Fiji where one of the passengers was so big that he couldn't fit into one of the oversized business class seats. You'd be surprised - sometimes it's really not just a matter of buying more space.

I think it's a problem on those really small twin-prop planes. I've seen people have to be offloaded from those flights because they were over the legal take-off weight. Sometimes, I'm sorry to say, the situation dictates it. I've had to provide my weight details before when getting on small charter flights.

As I understand it, the airlines estimate the average passenger is 80kg (~176 lbs). And while that may have been a valid assumption to make 20 years ago, I dare say that it's a gross underestimation these days.

The aircraft picture in that story is an Islander, about eight passengers, so I think you are right. My husband had to enter my weight for me once and put it as 65kg. I was indignant as he had transposed the digits, but what the hey, just meant the dodgy little aircraft was 9kg lighter.

Who knows what their baggage is going to weigh the day they buy the ticket? (Not me!)

Interesting! I understand what the problem is and in such extreme cases with very small planes and very obese passengers it does make sense. But there are also other solutions - on top of my head I can immediately think of 2: (i) increase the average estimated weight per passenger to something more realistic, (ii) set a extra fee for people above some weight limit. I can easily imagine cases in which paying with a rate proportional to your weight will turn out unfair e.g. 2 50 kg people occupy 2 seats but pay the same as one 100kg person. Or 1 person with 2 kids - those 3 seats have a price independent of the overall weight, no?

Idea (i) fails right from the start. Increasing the average weight per passenger means less passengers allowed per flight. Without reconfiguring the seating on every plane everywhere (to account for the larger bodies), this would mean flying with empty seats. Never going to happen given the small margins that airlines are already dealing with.

Idea (ii) - maybe. But for some, this still feels like discrimination for being of a lower weight. For someone who weighs 50kg and gets 20kg luggage allowance vs. someone who weighs (a still healthy) 65kg and gets a 20kg baggage allowance, it still feels unfair for the other person to get a "free" 15kg.

Personally, I like the idea, but I know it won't be popular and I don't see the major international airlines adopting it. I suspect it's something that may get implemented for the small twin-prop island hopper/charter flights around the world, but that's not really that much different to what they do already.

I can understand the reasoning, especially on smaller aircraft, but I certainly don't think it should be legal. First of all, there's gender discrimination, men tend to weigh more than women. And someone who is 6'5" is almost certainly going to weigh more than someone who is 5'2", and that has nothing to do with obesity. I understand the need to get the weight of the plane right on smaller aircraft, but I don't think an individual's weight should be reflected in their fees. That's just opening the door for a lawsuit. I'm someone who has always been a healthy weight and hates the increasing fees due to increasing waistlines, but let's be realistic.