A valid calculation starts with the individual aircraft
Two aircraft of the same model can have different empty mass and centre of gravity because of equipment, repairs and modifications. Use the current weighing report and approved data for the specific registration, with the correct arms, limits and envelope.
Registration, model and empty mass are not enough. You also need empty moment or CG, station arms, fuel data and the correct approved envelope.
Three fundamental quantities
| Quantity | Meaning | Relationship |
|---|---|---|
| Mass | Aircraft, occupants, baggage and fuel | Use one consistent unit |
| Arm | Distance from the manufacturer datum | Comes from approved data; the user does not choose it |
| Moment | Turning effect of a mass at its arm | Moment = mass × arm |
Centre of gravity equals total moment divided by total mass. If the manufacturer uses indices or reduced units, retain the exact approved conversion.
Data required in a complete aircraft profile
- Registration, model and current configuration.
- Empty mass and empty moment or CG.
- Seat, baggage and fuel-tank arms.
- Maximum ramp, take-off and landing masses.
- Forward and aft CG envelope limits.
- Usable fuel capacity, arm and approved conversion.
- Date and source of weighing data.
Calculate take-off and landing conditions
- Assign occupants and baggage to correct stations.
- Convert usable fuel volume to mass using the applicable method.
- Calculate take-off mass, moment and CG.
- Subtract trip fuel and its moment for landing.
- Verify both points against the envelope and all mass limits.
Fuel burn can move CG when tank arm differs from current CG. Lower landing mass is not automatically a more favourable condition.
Inside the envelope does not prove sufficient performance
NCO.POL.100 requires operation within approved limitations throughout flight. A valid balance point does not prove adequate runway, climb or landing performance. Also assess obstacles, density altitude, wind, surface and every AFM or POH limitation.
When data must be updated
Under NCO.POL.105, mass data must reflect current configuration. Modifications, repairs and equipment changes must be documented, and the aircraft reweighed when their effect cannot be determined accurately by calculation.
Before each calculation, compare profile date, registration and configuration with aircraft records.