Its pretty obvious to us novice airline users that an airplane has a maximum takeoff weight which is the total of the empty plane, plus fuel plus cargo plus passengers (okay I missed something). Thus I understand that a plane packed with passengers and cargo might not be able to fill its tanks with fuel and might not be able to travel for as many hours as the same plane with no passengers. That seems to be a pretty simple calculation.
But lets take a regular mainline plane like a 737. Say its half full of passengers and cargo and its going 1k miles. Can the airline calculate the additional fuel it would take if the plane was two tons heavier-or is it like my car-I know that it probably uses more fuel when I have five passengers and the trunk full but its virtually impossible to tell.
I ask this because of all of the whining about baggage charges. Obviously there is labor cost in loading an processing bags but is the system sophisticated enough to calculate the extra fuel cost of flying x pounds of cargo y miles.
If there is such a formula what would it cost in fuel to fly on 40 pound bad on a 2400. mile flight? and how does it compare to the charge for taking a bag?