Arm

An arm is the horizontal distance from the reference datum to the centre of gravity of a specific item or load station. The arm is used in conjunction with weight to calculate the moment of any load placed in the aircraft. Distances aft of the datum are typically expressed as positive values, while distances forward of the datum are typically expressed as negative values.

Key Points

• •Distances aft of the datum are usually expressed as positive values.
• •Distances forward of the datum are usually expressed as negative values.
• •Arms are measured in inches or millimetres depending on the aircraft flight manual.
• •Multiplying an arm by its associated weight gives the moment, which is used in centre of gravity calculations.

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