Introduction to Aircraft Mass and Balance
“During any phase of operation, the loading, mass and center of gravity (CG) of the aircraft shall comply with the limitations specified in the AFM, or the operations manual if more restrictive.”
CAT.POL.MAB.100 (Paragraph A)
The above paragraph obliges commercial operators to ensure that the Aircraft’s Weight and Balance parameters are always within the approved limits as specified in the Aircraft's Flight Manual during all flight phases.
The Weight of the Aircraft is composed of all the weights onboard of the aircraft. From basic physics we know that anything under the effect of the earth’s gravitational field having a mass has weight, which is normally attributed to the pull our planet Earth exerts on any object having any sort of mass. So the weight of the aircraft thus is composed of the weight of the airframe, the structure, the equipment and onboard instrumentation, engines, landing gears, passenger seats, lavatories, monuments, crew, passengers, cargo load and fuel. Basically anything on board the aircraft will contribute to the final weight of the aircraft and the final weight of the aircraft is always to be within those limits specified in the manuals.
Balance refers to the position of the aircraft’s center of gravity. That is, the imaginary point at which the aircraft could be hung in a stable position if it was possible to hang an aircraft from a single point.
A complication in relation to Aircraft Weight and Balance is the fact that this is very dynamic and they are changing all the time. Whenever a passenger moves inside the cabin, whenever the cabin crew move up and down the aisles with trolleys for cabin service, these are shifting weights around moving so also the center of gravity of the aircraft all the time, but perhaps the most significant dynamic effect of weight and balance is the weight from Fuel. An aircraft burns fuel to propel itself in flight and once fuel is burned that weight is no more on the aircraft.
Yet still, legislation is clear, even in this very dynamic environment Aircraft Mass and Balance are to be within the specified limit at all times.
Operational Empty Weight
In this paragraph I will try to explain what is the Aircraft’s Operational Empty Weight.
Once can think of an Aircraft’s weight being composed of two major components. The terms that will be used here are not really official terms but helps in explaining the idea of Operational Empty Weight.
The two major components of the Aircraft Weight are the fixed weight and the dynamic weight.
The fixed weight of an Aircraft, is the weight of those elements which are always onboard the aircraft during its service lifetime.
Examples of Fixed Weights on board the aircraft include:
- The airframe's structure;
- The major aircraft assemblies such as Landing Gears, Engines, Doors and panels;
- Emergency Equipment;
- Seats, Lavatories, Galleys and textiles inside the cabin;
- LRUs and equipment and instruments installed on the aircraft;
The dynamic weights on the other hand are the weight of the items which change from one flight to another and even change during a particular flight. Some examples of dynamic weight include:
- Passengers and their Luggage;
- Catering;
- Fluids such as Fuel, potable water and Human waste
- Cargo loaded in the Aircraft’s Cargo Hold/s.
In aircraft maintenance we need to determine the Aircraft fixed weight, which we call the “Operational Empty Weight, OEW” with high accuracy so as when the aircraft is in service, the responsible personnel and the Pilot in Command can calculate the dynamic elements added on top of the OEW to ensure and verify that the total weight of the aircraft is within the specified limits at all time during all phases of the intended flight.
As a matter of fact CAT.POL.MAB.100 Paragraphs (b and c) states:
“The operator shall establish the mass and the CG of any aircraft by actual weighing prior to initial entry into service and thereafter at intervals of four years if individual aircraft masses are used, or nine years if fleet masses are used.
The accumulated effects of modifications and repairs on the mass and balance shall be accounted for and properly documented. Aircraft shall be reweighed if the effect of modifications on the mass and balance is not accurately known.
The weighing shall be accomplished by the manufacturer of the aircraft or by an approved maintenance organization.”
It is the responsibility of the Operator’s CAMO to ensure that any changes to the aircraft Operational Empty Weight are accounted for and that the Operator’s Flight and Ground Operations Departments are kept up-to date with latest weight and balance data for each and every aircraft in the operator’s fleet. In any case an aircraft is to be weighed by an approved Part-145 maintenance and repair organization every 4 years or 9 years, if fleet averages are used.
Aircraft Weighing during Maintenance
Aircraft Weighing is normally included in a work pack by the responsible CAMO. The CAMO or the operator of the aircraft needs to provide the exact configuration of the aircraft in which the aircraft is to be weighed and the MRO is then responsible in ensuring that the aircraft is properly configured following the CAMO’s or operator’s configuration, weighed following the approved maintenance data and calculating the resulting weight and centre of gravity position.
The calculation of the aircraft weight and balance parameters following weighing is to be carried out meticulously as this will then be used in flight operations. A miscalculation during aircraft weighing can cost dearly and it is therefore extremely important that whoever performs aircraft weight and balance analysis is trained, experienced and competent on this topic.
Our Aircraft Weight and Balance training course is intended to support maintenance personnel performing aircraft weighing and/or aircraft weight and balance calculations build the necessary knowledge, confidence and competence to accurately and efficiently perform this safety critical task.
For further information follow the link below and do not hesitate to contact us through our dedicated form in case of any queries.
