Moving Mass and Ballast - ATPL 031 — Mass & Balance

Sooner or later a load sheet comes out wrong: the CG a whisker beyond a limit, or parked somewhere that costs fuel. The cures are physical, and they are this lesson: shift load from one compartment to another, or add or remove ballast. Both obey one small piece of algebra, worked here in every direction the exam asks, together with the ground procedures that make sure the cargo really is where the paperwork says, and the check to run when it turns out not to be.

The shift formula

Moving a mass inside the aircraft changes no total, only the balance: the aircraft's moment changes by the item's mass times the distance it moved, and dividing by the total mass gives the CG's response. Rearranged into its exam form:

The proportion reads in every direction: the fraction of the total mass you move equals the fraction of the item's travel that the CG copies. The CG always moves the same way as the shifted mass, and the formula's four quantities give the exam four questions: any three given, find the fourth. Two of them have their own LOs and their own worked chains below.

Ballast: adding and removing mass

When nothing aboard can move, mass is added, or taken off. Ballast changes the total, so the shift formula no longer applies as it stands; the working relation balances the newcomer's moment about the new CG against the whole aircraft's change:

Is the cargo where the paperwork says?

Every formula above trusts one assumption: that the load is physically where the documents claim. The ground system exists to make that true. The loading instruction tells the ramp team what goes in which compartment; the loading supervisor confirms the holds against it and signs the loading report, and that confirmation flows into the load sheet the commander accepts. Unit load devices (ULDs) carry tags matched to the instruction, compartment by compartment, and any discrepancy, a pallet in the wrong hold, a container that never arrived, must be reported and resolved before departure, because the load sheet's CG is a fiction until the holds match it.

Calculate the mass to move between given compartments, or the distance to move a given mass, to establish a required CG

Calculate the ballast to add or remove at a given position, or the position for a given ballast, to establish a required CG

Describe the methods that verify cargo is loaded as the loading manifest and instruction require

Determine whether the CG remains within limits after cargo is loaded in the wrong order or location

The shift formula

Check you understood

Ballast: adding and removing mass

Is the cargo where the paperwork says?