# Repositioning the CG: Mass-Shift Formula and Practical Corrections

> Learn to correct out-of-limit CG conditions by moving load using the mass-shift formula, with direction logic and practical cargo-repositioning examples.

- **Subject:** 031 — Mass and Balance
- **Section:** 031-05 — Determination of CG Position
- **Topic code:** 031-05-03
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/mass-and-balance/determination-of-cg-position/repositioning-of-cg/

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## Shifting Mass

If the calculate CG is outside the limits, load (passengers or cargo) can be moved to bring the CG back into the safe envelope.

### The Formula

The change in CG position ($\Delta CG$) is proportional to the mass moved and the distance it is moved, relative to the total mass of the aircraft.

$$
\Delta CG = \frac{\text{Mass Moved} \times \text{Distance Moved}}{\text{Total Mass}}
$$

*   **Mass Moved**: The weight of the item being shifted.
*   **Distance Moved**: The distance between the old location and the new location of the item.
*   **Total Mass**: The total mass of the aircraft (which remains constant during a shift).

### Direction of Shift
The CG moves in the **same direction** as the mass being moved.
*   Move load **Aft** $\rightarrow$ CG moves **Aft**.
*   Move load **Forward** $\rightarrow$ CG moves **Forward**.

## Example

*   Total Mass: 10,000 kg
*   Current CG: 200 inches (Too far aft)
*   Desired CG: 195 inches (Need to move CG 5 inches forward)
*   Distance available to move cargo: 200 inches (e.g., from rear hold at 300" to fwd hold at 100")

How much cargo must be moved?

$$
\Delta CG = 5 \text{ inches}
$$
$$
5 = \frac{\text{Mass Moved} \times 200}{10,000}
$$
$$
\text{Mass Moved} = \frac{5 \times 10,000}{200} = 250 \text{ kg}
$$

**Action**: Move 250 kg from the rear hold to the forward hold.

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Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.