Balancing Act: Aircraft Weight and Center of Gravity

Accurate Weight and Balance (W&B) data is essential for safe and efficient aircraft operations. ICAO Annex 6 requires that the weight of the aircraft and the Centre of Gravity (CG) location are such that the flight can be conducted safely. Once the operator knows the empty weight and position of the CG, by adding passenger, cargo, and fuel loads, the weight of the aircraft and CG can be estimated for the entire flight.

For a new aircraft, the weight established during production is documented in a Weight and Balance Report provided by the Type Certificate Holder (TCH) or made available to the operator, forming the baseline for subsequent management.

The aircraft tends to gain weight over its operational life due to various factors: accumulation of grease and oil, repaint, new equipment, modifications, and repairs. The operator is responsible for ensuring that the weight and balance records are updated whenever such changes occur.

The Weight & Balance can be obtained by:

• actual weighing the aircraft, or

• calculation from the previous aircraft weighing if the changes are known.

In practice, the operator shall establish the weight and CG of the aircraft by actual weighing prior to initial entry into service (credit may be taken from a previous weighing if the records have been properly adjusted for any alterations or modifications). Thereafter, weighings must be conducted at specified intervals. The accumulated effects of modifications and repairs must be tracked and documented. The aircraft should be reweighed if the impact on weight and balance cannot be accurately calculated.

Scheduled Requirements

ICAO does not establish specific periods for aircraft weighing but recognizes the importance of developing a program to satisfy Annex 6 requirements.

EASA Air Ops CAT.POL.MAB.100(b) requires that the operator establish the weight and CG of any aircraft at intervals of 4 years if individual aircraft masses are used, or nine years if fleet masses are used.

FAA 14 CFR 125.91 requires that the current mass and CG are calculated from the values established by the actual weight of the aircraft within the preceding 36 calendar months but may be extended up to 48 months if cumulative limits are met (see “Impact of Modifications and Repairs” below for details on these limits). For fleet mass programs, the operator should establish a time limit such that all aircraft in the fleet are eventually weighed. Based on typical fleet service life, this limit should not exceed 18 years (six 3-year weighing cycles)

As a scheduled action with a direct effect on airworthiness, it is recommended to incorporate and monitor the Weight & Balance task within the Aircraft Maintenance Program (AMP), referencing the corresponding regulatory requirement.

Fleet Masses

In line with ICAO Airworthiness Manual Doc 9760 recommendations, EASA AMC1 CAT.POL.MAB.100(b) and FAA AC 120-27F provides guidance for using fleet masses for a group of aircraft of the same model and configuration under certain conditions. The interval between two fleet mass evaluations should not exceed the interval for individual weighing (48 months in EASA environment, and 36 months in FAA), and during that time the operator should weigh a certain number of aircraft (where n is the number of aircraft in the fleet):

• Fleet of 2 or 3 aircraft: n

• Fleet of 4 to 9 aircraft: (n+3)/2

• Fleet of 10 or more aircraft: (n+51)/10

Aircraft selected should be those that have not been weighed for the longest time.

Impact of Modifications and Repairs

Modifications and repairs can change the aircraft’s weight and balance. The total effect of these changes between scheduled weighings must be tracked and recorded. If the dry operating weight changes by more than ±0.5% of the maximum landing weight, or the CG shifts more than 0.5% of the Mean Aerodynamic Chord (MAC), the weight and balance must be updated. This can be done by calculation using approved data or by reweighing the aircraft.

For most aircraft modifications, a mathematical calculation of the W&B change is practical. For some modifications, such as interior reconfigurations, the large number of parts removed, replaced, and installed may make an accurate determination of the W&B change by computation impractical.

Conclusion

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