14.106 Definitions, Terminology and Abbreviations

14.106.2 Explain the meaning of the following terms:

(a) arm (moment arm);

The arm is the horizontal distance from the datum to the centre of gravity of an item.
It is used in weight and balance calculations to determine moment.

Units: inches, feet, centimetres, etc.

(b) datum;

The datum is an imaginary vertical reference plane or point from which all arms are measured.
It may be located at, ahead of, or behind the aircraft.

(c) moment (including units used);

A moment is the turning effect produced by a weight acting at a distance from the datum.

Moment = Weight × Arm

Units:

• lb-in (pound inches)
• lb-ft (pound feet)
• kg-cm (kilogram centimetres)

(d) centre of gravity (C of G);

The centre of gravity is the point at which the aircraft’s total weight is considered to act, and around which the aircraft would balance.