[WalterBright]

> I have been on a few non-commercial flights, and they always make me step on a scale before I get on the plane.

The weight variation makes a big difference for smaller airplanes. Big airplanes can use a statistical average for weight calculations, but small ones cannot.

The weight calculation is necessary to compute fuel load and takeoff distance, for example.

As I recall, there was a major airline crash once because the airplane was overweight compared to its calculated weight. Since then the airlines revised the average passenger weight upwards.

[jevinskie]

And the smallest planes have to worry about distribution of passenger weight to maintain proper balance.

[seanmcdirmid]

This much more than what parent stated.