Weight and Balance

The mechanic or repairman who keeps the airplane safe records changes that occur due to repairs or alterations. He is responsible for retaining the weight and balance records up to date. Finally, the pilot in command (PIC) has to know the maximum allowable weight of the aircraft and its CG limits before each flight. It helps him to determine the necessary aircraft load control actions during the flight.

Understanding and following W&B control requirements can significantly diminish general aviation accidents. If an aircraft becomes overloaded or imbalanced, it will require more power, and as a result, it needs greater fuel consumption to continue its flight correctly. Additionally, suppose we neglect the effects of weight and balance on the aircraft’s performance. In that case, negative factors such as high-density altitude, bad weather conditions, low engine power, severe maneuvers, and urgent situations can easily lead to an accident.

As mentioned above, the most significant feature of the automated load control system is reducing errors and time consumed in manual W&B processes; thus, improving efficiency and reinforcing safety. There are lots of other features for automated W&B, which distinguish between different vendors. The most important ones are as follows:
• Automatic calculation of necessary weight and balance
• The ideal trim calculation for minimum fuel consumption
• Real-time display of MAC, ZFW, TOW, and CG envelope
• Dynamic calculation of the center of gravity
• Passengers distribution option
• Provides all required documentation based on IATA standards
• Generating an out of range alarm for MAC point
• Weight and balance tutorial and training

The centralized load control structure is a standard system that is more streamlined and consistent. Using a centralized load control system provides some benefits. Centralizing human sourcing will increase productivity. In addition, the fewer load controllers in this structure enhance the process efficiency.

This safety area in which the aircraft operation can be properly is called the weight and balance envelope.
An operationally convenient format for representing this safety range is on a graph of weight vs. moment. The principle of this format is that the weight (or mass) changes and vectors show their corresponding moment changes.

As mentioned before, the weight and distribution of the payload and fuel determine the CG position. During the flight, the CG position changes by fuel consumption and movements of passengers and crews about the cabin. The CG vertical motion along the airplane is small and negligible. Still, the horizontal motion is significant, and it should remain within determined fore and aft limits for each phase of flight. The lateral position of CG is another main parameter that must be in a specific range relative to the payload (especially freight loading).

Weight and Balance Sheet Airlines and ground service companies usually provide customized calculations regarding the determination of CG envelope, zero fuel CG position, and take-off CG position in an excel format based on their operational program. Users can conveniently calculate and determine the CG position based on different operational factors of the specific program using the weight and balance excel spreadsheet.

Mean Aerodynamic Chord (MAC)

Mean Aerodynamic Chord (MAC) or the reference chord (RC) are usual terms in all the limitations and the definitions related to weight and balance aspects. For example, CG position is usually expressed in terms of the percentage of MAC (with the symbol of %MAC). CG safe limits are represented in terms of %MAC too. The MAC is a reference line used in the design of the wing; its position is relative to the branch, and the fuselage is accurately known. The location and dimensions of this reference line are defined using the AHM 565.
· MACTOW: The center of gravity for Takeoff Weight expressed as a percent of the Mean Aerodynamic Chord (%MAC).
· MACZFW: The center of gravity for Zero Fuel Weight expressed as a percent of the Mean Aerodynamic Chord (%MAC).

The AHM content is intended as guidelines and recommended practices. It also provides standards and templates (all designed to assist and guide appropriate staff on the “what to do” aspects of airport operations). The most important part of the AHM for weight and balance purposes is called AHM565, which contains the format and structure of aircraft data for the weight and balance definitions.

Airplane Operational Weights

The definitions of aircraft weights vary for different financial accounting procedures based on individual elements, or components, assigned to specific categories. Therefore, there is a narrow margin in weight accounting procedures used by different manufacturers and operators. The following terms are the typical breakdown of an airplane operational weights:

Max Gross Weight

For a specific type of aircraft, there is a maximum gross weight that the total weight of the airplane must be no greater than it during the flight.

Manufacturer’s empty weight (MEW)

The manufacturer’s empty weight (MEW) is the weight of the basic aircraft structure plus the fixed equipment and systems that are the internal parts of the aircraft along with power plant, systems (e.g., avionics, hydraulics), furnishings (e.g., passenger seats), seller furnished emergency. In other words, it is essentially a “dry” weight, including only those fluids contained in closed-circuit systems (e.g., hydraulic systems).

Operating Empty Weight (OEW) or Dry Operating Weight (DOW)
The Operating Empty Weight (OEW), which many operators call the Dry Operating Weight (DOW) or Basic Operating Weight, is the weight of a configured aircraft for a particular operation (mission). OEW excludes usable fuel and payload (cargo, luggage, passengers, stores, service loads such as meals and beverages). It is the BEW plus the weight of the staff and the equipment and supplies necessary for a specific mission (operation) such as crew’s manual and baggage, catering supplies, cabin service items (e.g., blankets, newspapers, and other literature), replenishable fluids and chemicals (e.g., for toilets), engine and other oils, additional emergency equipment (e.g., life rafts for overwater routes), tool kits, cargo containers, and pallets. Operating empty weights vary based on every special mission (not aircraft type).

Ramp Weight or Taxi Weight
The ramp weight (or taxi weight) is the take-off weight plus the weight of the fuel needed for the auxiliary power unit (APU) usage before take-off, including engine start and run-up and taxi to the take-off run.
Landing Weight (LW)
The Landing Weight (LW) is the airplane weight at touchdown at the destination airport. From a flight planning perspective, it is equal to the zero fuel weight plus the weight of the reserve.
The above terms have absolute limits depending on the structural capability of an aircraft in different conditions. Production standards dictate these maximum limits, and they are known as “structural-limited weights.” In some cases, it is possible to enhance the weight limits through approved modification for earlier manufactured aircraft. Structural-limited weights are listed below:
• Max (Design) Taxi Weight
• Max (Design) Take-off Weight
• Max (Design) Landing Weight
• Max (Design) Zero Fuel Weight
It is worth mentioning that the max weights that operators use are called “Certified Weights” or “Purchased Weights” (the weights that are recorded in the airplane flight manual). These weights are selected by the operator when the plane is purchased. The Certified Weights are usually less than corresponding design structural limit weights due to operational or financial reasons. It is possible to increase the Certified Weights up to structural limit weights at any time (usually at a price).