Mass and Balance Fundamentals and Definitions
Why mass and balance matters
Every aircraft has a maximum mass it can safely support and a limited range of centre of gravity (CG) positions within which it remains controllable. Mass and balance is the discipline of ensuring both limits are respected before every flight. Candidates must be fluent with the core vocabulary: mass (the quantity of matter, expressed in kg), weight (mass × gravitational acceleration, a force in newtons), empty mass, operating mass, payload, fuel mass, take-off mass (TOM), landing mass (LM) and zero-fuel mass (ZFM). In aviation practice the terms "weight" and "mass" are often used interchangeably, but exam questions may test the distinction.
Building up the mass
A standard build-up runs: basic empty mass + crew + crew baggage + catering/removable equipment = dry operating mass (DOM). DOM + traffic load (passengers, baggage, cargo) = zero-fuel mass. ZFM + usable fuel = take-off mass. TOM − trip fuel = landing mass.
Traps to watch
- Unusable fuel is already included in the basic empty mass; adding it again is a classic error.
- Dry operating mass excludes all usable fuel but includes crew and operational items.
- Traffic load is passengers + baggage + cargo, not fuel.
- Questions may give mass in lb and ask for kg; convert consistently (1 kg ≈ 2.2046 lb).
- Distinguish maximum structural limits from regulated performance limits.
Worked example
Basic empty mass 9,200 kg; crew 170 kg; catering 80 kg; passengers 1,200 kg; baggage 300 kg; cargo 400 kg; fuel 1,100 kg. DOM = 9,200 + 170 + 80 = 9,450 kg. ZFM = 9,450 + 1,200 + 300 + 400 = 11,350 kg. TOM = 11,350 + 1,100 = 12,450 kg. If trip fuel is 700 kg, LM = 11,750 kg.
Rule of thumb
Always build the mass table in a fixed order: empty → operating → zero-fuel → take-off → landing. This exposes any double-counting immediately.