We're used to being charged more for heavier bags, but what about the people carrying them?
Well, in the Journal of Revenue and Pricing Management, Dr Bharat P. Bhatta looked at how airlines could charge overweight fliers more.
It might sound like an idea that has fat chance of succeeding, but it makes sense. For airlines, every extra kilogram means more expensive jet fuel must be burned, which leads to CO2 emissions and financial cost.
And it's not just a pipe dream. Samoa Air now charges its passengers by the kilogram. You pay 1 tala (29p) a kilo - traveller and baggage combined - on the airline's shortest route and 3.8 tala (£1.10) for the longer routes.
This is the fairest way of travelling. There are no extra fees in terms of excess baggage or anything - it is just a kilo is a kilo," chief executive Chris Langton told ABC Radio.
Dr Bhatta put forward three ideas for pay-as-you-weigh pricing.
The first is a straightforward price per kilogram for both passengers and their luggage. A passenger’s luggage and body weight would be calculated, with the fare comprising a per kilo cost. This is the one Samoa Air is using.
The second idea is a 'base fare' plus or minus an extra charge. Airlines would set a fixed low fare, with heavier passengers paying a surcharge and lighter passengers being offered a discount.
The professor's final suggestion is for passengers to have the same fare if they have an average weight, but this could be discounted for weights below a certain limit or added to for excess weight above it. This would result in high, average and low fares for each flight.
His suggestions received the backing of 48% of those questioned in a poll by the website Holiday Extras. Over half (51%) of men were in favour of overweight people paying more to fly, compared to 43% of women.
The case for the fat tax
One particular personal incident makes me think an airline 'fat tax' is a great idea. I was on the second leg of a long journey to Costa Rica (not that I’m one to name-drop exciting travel destinations, you understand) and was seated in the middle seat of a row of three.
My hopes of a relaxing journey were cruelly dashed when a very overweight American man headed for the seat next to me. “Can I move the armrest?” he asked - it was clearly impossible for him to sit down otherwise.
To this day I am at a loss as to why I just agreed and dutifully raised the armrest. The next four hours were spent grumpily squashed into half my seat, cursing my lack of assertion, while the fat man spilled over into my seat.
As well as spending the whole flight cramped and uncomfortable, I was angry. I’d paid almost £1,000 for a plane ticket yet had somehow ended up with half a seat. And as for health and safety, this guy wasn’t going anywhere in a hurry, even if the plane was on fire.
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The fat issue
Passenger obesity has become a big issue for airlines over the past few years. Around 22% of Brits are now classed as obese, compared to 32% of Americans.
In simple terms, the heavier the flight the more fuel a plane needs. Supposedly that’s why passengers are charged for excess baggage, although obviously it’s a money-making exercise too.
Some airlines already have policies that require obese customers to pay more. US-based Southwest Airlines has a “Customers of Size” policy, which requires passengers to buy a second seat if they can't fit between the armrests. Southwest's seats measure 17 inches across.
Samoa Air, of course, charges travellers by weight rather than pay for a seat.
Would a fat tax work?
In theory, making passengers who need more than one seat on a plane pay for an extra seat sounds like a good idea. But monitoring and implementing such a strategy is another issue altogether.
Essentially, judging people on weight rather than size is a flawed concept. If scales were introduced at the check-in desk it could result in some perfectly proportioned people being accused of being overweight.
The most widely recognised way to calculate whether someone is over or under-weight is body mass index (BMI).
Your BMI is calculated by dividing your weight in kilograms by your height in metres squared. The trouble is BMI doesn’t take muscle mass and body-fat percentage into account. According to BMI calculations former England rugby player Jonny Wilkinson was overweight when he was at his prime.
Measuring someone’s waist circumference would be a much better way to assess passengers rather than simply making them get on the scales. Or airlines could simply see if a passenger fits in a single seat - and make them buy another seat if they don’t.