[1][2][3] An aircraft's gross weight will decrease during a flight due to fuel and oil consumption.
An aircraft's gross weight may also vary during a flight due to payload dropping or in-flight refuelling.
The structural weight limits are based on aircraft maximum structural capability and define the envelope for the CG charts (both maximum weight and CG limits).
At this weight, the subsequent addition of fuel will not result in the aircraft design strength being exceeded.
[5] Maximum flight weight is limited by aircraft strength and airworthiness requirements.
Typically it is the same as the maximum takeoff weight (notable exception is due to inflight refueling).
It is greater than the maximum takeoff weight due to the fuel that will be burned during the taxi and runup operations.
In operation, the maximum weight for takeoff may be limited to values less than the maximum takeoff weight due to aircraft performance, environmental conditions, airfield characteristics (takeoff field length, altitude), maximum tire speed and brake energy, obstacle clearances, and/or en route and landing weight requirements.
Overweight landings require a structural inspection or evaluation of the touch-down loads before the next aircraft operation.