What is the definition of "datum" in aviation?

In aviation, "datum" refers to an imaginary plane used for reference in measuring the center of gravity (CG) of an aircraft and determining weight and balance calculations. The datum provides a consistent starting point from which measurements are taken for the arm, which is the horizontal distance from the datum to the center of gravity of various components of the aircraft. This reference point is crucial in ensuring the aircraft operates within safe limits, effectively managing its balance and stability during flight.

Using a datum allows pilots and ground crew to accurately compute the CG and make necessary adjustments, such as moving cargo or adjusting fuel load, to maintain the aircraft's balance. Understanding the datum also aids in the identification of different loading conditions and their impact on the aircraft's performance.

While other options mention points or weights related to the aircraft, they do not capture the fundamental role that the datum plays in aviation. The definition encompasses the concept of an imaginary reference plane rather than a tangible point or specific measurement of weight, which is essential for accurate weight and balance calculations.