@anne. As far as I am aware, all luggage is weighted & the expected weight of people is based on years&years of meta data for exact calculations. Also airplane pilots captains are the ones responsible for calculating the amount of fuel needed for each flight. I am an absolute believer in Business Optimization/Efficiency (have years&years of experience managing & implementing this for large multinational organisations). But in this case, while not claiming to be some expert in this field, I know that having enough fuel is also a huge safety precaution in the aviation industry. For example the rare case IF a plane (for whatever reason) cant land at the destination airport (or has to redirect its flight path to another airport)..... I'd rather reach my destination alive instead of pieces of me in a plastic body bag, then some a-hole or a-hole company "saving on fuel" for costs or CO2 reduction ;-)

There is very little variation in the weight of all passengers and their luggage, especially when you are talking about the high number of passengers on board of commercial flights. This small variation becomes completely insignificant in comparison to the total weight of a fully loaded airplane. Many other factors like the additional fuel for turning circles if the plane cannot land immediately are much more important than a few kilograms of load.

Fuel is the biggest cost for airlines, right up there with salaries. So there is massive incentive for the airlines and designers to make them as efficient as possible. Trust me, if there's a way to save on fuel, it's being done.

Sounds somewhat nonsense/overstated. Because it's super cheap & easy to retrofit (put a pressure sensor on the hydraulics of each wheel; read measurement after boarding before fueling). So. That means the whole scheduling is messed up (you fuel somewhere between landing and final boarding; truck may come in 2min or in 30min) and often you'd miss your takeoff slot. THEN I doubt offhand it would make much difference, as on a simple bicycle and average speed 85% of energy goes to wind resistance (which increases as a square of the speed) so at aircraft speeds it's even more dominant (yes air pressure lower at high altitude, but it's 500mph+).

except you need to make emergency landing, or weather is bad and you need to turn around