In weight and balance terminology, the datum serves as the reference point for which calculation?

• A. Center of gravity reference point
• B. Nose gear alignment
• C. Engine thrust reference
• D. Aft fuselage reference

Answer: (D)

In weight and balance, the datum is the reference point from which all longitudinal arm measurements are taken. For each item on the aircraft, you multiply its weight by its arm (distance from the datum) to get that item’s moment. Adding up all those moments and dividing by the total weight gives the center of gravity along the longitudinal axis. The datum’s location is chosen by the aircraft designer and can be anywhere along the fuselage to simplify calculations; some designs place it near the aft fuselage for convenience, but the key idea is its role as the reference point for calculating moments, not the CG itself or features like nose gear alignment or engine thrust.