What is an 'arm' in weight and balance calculations?

• A. The distance in inches from the datum to the weight’s location.
• B. The weight of the item.
• C. The height of the item above the floor.
• D. The moment of the item.

Answer: (D)

An arm is the distance from the chosen datum to the weight’s line of action. It’s the lever arm used in weight and balance calculations. This distance, measured along the aircraft, tells you how far the weight is from the reference point, and it’s what converts weight into a moment when you multiply weight by arm. So the moment of an item is weight × arm, and all such moments sum to give the total moment for determining the center of gravity. The arm is not the weight itself, nor a height above the floor, nor the moment itself.