What does "arm" refer to, in relation to weight?

"Arm" refers specifically to the distance from the center of gravity (CG) of the aircraft to a designated reference datum. This measurement is crucial for determining how weight is distributed throughout the aircraft and for calculating the moments that affect the aircraft's stability and control.

When performing weight and balance calculations, understanding the arm allows pilots and technicians to assess how different loads (such as passengers, cargo, and fuel) influence the aircraft's center of gravity and overall balance. The location of the CG relative to the reference datum is vital to ensure safe operation, as an improperly balanced aircraft can lead to handling difficulties and potential hazards during flight.

The other choices do not correctly define "arm": the aircraft's weight refers to the total mass of the aircraft, the total weight carried pertains to the weight of all items onboard, and the overall length is a simple measurement of the aircraft’s size without relation to the CG or its balance.