Module 7.16 Aircraft weight and balance

Knowledge levels

Item	A	B1 / B3	B2 / B2L
7.16(a) Calculation of centre-of-gravity/balance limits; use of relevant documents	—	2	2
7.16(b) Preparation of aircraft for weighing; aircraft weighing	—	2	—

Why it matters

• An aircraft must be within its maximum weights and its centre of gravity (CG) must stay within the forward and aft limits given in the type certificate data / flight manual.
• CG too far forward: higher stick forces, difficulty rotating and flaring, higher stall speed, more tail-down force (more drag, more fuel).
• CG too far aft: reduced longitudinal stability, risk of loss of control, especially at low speed; possible tail tipping on the ground.
• Maintenance changes (repairs, modifications, equipment removal or installation, paint) alter weight and CG and must be recorded.

Terms

Term	Meaning
Datum	imaginary vertical reference plane from which all horizontal distances (arms) are measured; set by the manufacturer (nose, firewall, or a point ahead of the aircraft)
Arm	horizontal distance from the datum to the item's CG; positive aft, negative forward of the datum
Moment	weight × arm (kg·m, lb·in)
CG	total moment ÷ total weight
Basic empty weight (BEW)	airframe, engines, fixed equipment, unusable fuel, full operating fluids (e.g. full engine oil, per the definitions used)
Operating empty / dry operating weight	BEW + crew, catering and operator items
Useful load	payload + usable fuel (+ crew in some definitions)
MTOM / MTOW	maximum take-off mass
MZFW	maximum zero-fuel weight (limits wing bending)
MLW	maximum landing weight
%MAC	CG expressed as a percentage of the mean aerodynamic chord: %MAC = (CG − LEMAC) / MAC × 100
Tare	weight of chocks, blocks, jacking adapters on the scales - subtracted