Aircraft Weight & Balance
Centre-of-gravity and balance-limit calculation, the weighing procedure and precautions, and the weight-and-balance documentation.
Weight & balance — summary notes
Free- Weight and balance establishes the aircraft's empty weight and centre of gravity (CG) and confirms the CG stays within the forward and aft limits for every loading — a CG outside limits makes the aircraft unstable or uncontrollable.
- The DATUM is a defined reference plane; the ARM is the horizontal distance of a weight from the datum, and the MOMENT is weight × arm. The CG is the total moment divided by the total weight, measured from the datum.
- Weighing procedure: use the approved weighing schedule, put the aircraft in the defined configuration (fuel and fluids drained or accounted for, specified equipment fitted/removed, state recorded), and use calibrated, in-date load cells or scales at the jacking or wheel points.
- Weigh in a closed, draught-free, dry hangar to avoid wind and rain errors, and level the aircraft to its datum using the built-in level provision.
- Record the reaction at each weighing point and its arm; sum the moments and divide by the total weight to find the empty-weight CG, then compare against the limits.
- Account for TARE — the weight of chocks, jacks and adapters on the scales — and subtract it, and record the true empty-weight configuration.
- The weight-and-balance report and the loading/mass-and-balance documentation are updated and certified after any weighing or major modification affecting weight.
- ⚠ Exam trap: Moment = Weight × Arm, and CG = Σ Moments ÷ Σ Weights measured from the datum — and remember to remove tare.
- Moment
- Moment = Weight × Arm
- Centre of gravity
- CG = Σ Moments ÷ Σ Weights (from the datum)
- Net weight
- scale reading − tare = actual reaction
Datum at the nose. Nose gear 500 kg at arm 1.0 m; main gear 1500 kg at arm 5.0 m. Find the CG.
Total weight = 2000 kg. Total moment = (500 × 1.0) + (1500 × 5.0) = 500 + 7500 = 8000 kg·m. CG = 8000 ÷ 2000 = 4.0 m aft of the datum.
Why is the aircraft weighed in a closed hangar and levelled to its datum?
Wind produces aerodynamic lift or download and rain adds weight, both falsifying the reading, so the hangar must be draught-free and dry. Levelling to the datum ensures the arms used in the calculation match the schedule; an out-of-level aircraft gives wrong arms and therefore a wrong CG.
Weight & balance concept map
FreeWeight & Balance
Weight & balance quiz
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