Flight Operations - Loadsheet

Nowadays, aircraft weight and balance is done by highly sophisticated software and used by both airlines and independant handling companies. Nevertheless, there are still large airline companies which use these loadsheets as a primary or just to crosscheck. As already pointed out earlier, the operational department, or "operations", use complex systems to perform weight and balance calculations. In case of a system shutdown or computer failure, manual loadsheets for each type of aircraft are present. Manual loadsheets are the same as digital loadsheets altough it requires more effort to complete. A loadsheet actually consists of two parts: the weightsheet to calculate all limiting weights and the trimsheet to calculate the trim capabilities of the aircraft and the loction of the "Center of Gravity" (CoG).

The following explanations are based on a loadsheet of the Boeing 777-200(ER).
Click here to open the loadsheet...


Weightsheet
A weightsheet is used to calculate the weights like fuel and payload, and is located on the entire left side of the loadsheet. At the beginning of the weightsheet, basic information like telex-addresses, date, flight number, aircraft registration and configuration must be filled in (1). Every aircraft has its own specific basic weight and index. These weights are the basis to make further calculations possible (2). The maximum weights of the aircraft in combination with the fuel will be used to calculate the allowed traffic load (3). The allowed traffic load is the payload allowed and prevents exceeding any of maximum weights. The next box contains payload information (4). Information about passengers, cargo and its distribution are described in this section. With the total weight of the traffic load and the aircraft weight, actual aircraft weights can be calculated (5). Last minute changes can be made in the last minute changes box next to the actual weights box (6). Supplementary or notes can be written in the concerning boxes (7). In combination with the trimsheet, the necessary information about weight and balance can be handed to the flight crew.

Making a loadsheet requires understanding about the weights integrated on a weightsheet and may not be created by an unlicenced person. Fuel weights, maximum weights and operating weights are items preprinted on a weightsheet. With these weights and payload weights, the actual weights can be calculated.

Fuel Weights
The fuel needed for a specific flight is commonly subdivided into different amounts and are related to the phase of flight, like block fuel, taxi fuel, trip fuel and alternate fuel. Block fuel is the total amount of fuel on board. Alternate fuel is not present on a weightsheet as it is already included in the block fuel. When taxiing to from stand to the runway, taxi fuel will be used. The block fuel minus the taxi fuel is the take-off fuel. Fuel used during the trip is called trip fuel.

Maximum Weights
Aircraft are limited by strength and airworthiness requirements, therefore maximum weights are established. The most important are: Maximum Zero Fuel Weight (MZFW), Maximum Take-Off Weight (MTOW) and Maximum Landing Weight (MLW).
The MZFW is the maximum weight of the aircraft without fuel. The MTOW is the maximum weight allowed before commencing take-off. A landing demands high loads to the landing gear, therefore the MLW is applied.

Operating Weights
The basic weight of an aircraft is called the Basic Operating Weight (BOW). This weight is the aircraft without standard operating items like passive/deadhead crew, pantry, fuel, payload or ballast. If the standard operating item adjustments are made the weight is called Dry Operating Weight (DOW). Dry because no fuel is added so far. When adding the take-off fuel the weight is called operating weight. The operating weight contains the weight of the aircraft plus standard operational items and fuel.

 

Trimsheet
Once the pilot or operator is sure the aircraft does not exceed any weight limitations it is necessary to conduct a trim analysis in order to determine the position of the CG. When loading an aircraft, it is not just a matter of how much is loaded into the aircraft, but where you put it as well. The location of the CG is critical to aircraft stability and elevator effectiveness. Loading an aircraft in such a way that a nose heavy situation is likely to happen will make it less easy to handle inflight, especially when commencing take-off or landing. If the aircraft is tail heavy, there is a risk of tip-over and will most certainly cause structural damage to the aircraft itself. This means that improper balance of the load carried by the aircraft could result in serious control problems and unsafe situations both on the ground as in flight. These kind of situations should be avoided at all times by making sure that the location of the CG lies between predetermined limits provided by the manufacturer. These CG limits are the forward and aft centre of gravity locations within which the aircraft must be operated at a given weight. The CG limits are commonly called the CG envelope or range. In order to find out where the actual CG is located and how the aircraft should be trimmed in order to make it more comfortable to fly, a so called trim sheet should be filled in.

Every segment of the payload carried on the aircraft has a certain arm from a specified datum. All data together decides whether the aircraft is either in or out of balance. The trim sheet calculates moments for each specific payload segment like the fuel load, passengers, baggage or cargo. First, a dead load and passenger index table is used to determine the effect of these weights on the change of CG (8). The passenger compartment configuration is an important factor when calculating the actual CG. A configuration that accommodates business class passengers means a less forward CG as cabin density decreases (9). Second, the trim chart is used to determine the CG at Zero Fuel Weight (ZFW) (10). After fuel is loaded, a fuel index correction is accomplished and plotted into the trim chart in order to determine the CG at Takeoff Weight (TOW) (11). Should these points lie between pre-described limits, the aircraft is in balance when loaded according to these calculations. From this point on, trim tab setting, take-off run data and landing data can be calculated and cross checked.

From the statements above it is quite easy to understand that the CG has to be located between defined limits in order to fly safely and legally. These limits can be expressed as a percentage of the Mean Aerodynamic Chord (MAC). MAC is the chord of an imaginary rectangular wing that has the same aerodynamic characteristics as the actual wing (figure 1). In effect, this imaginary wing replaces the more complicated plan form of the actual wing for calculation purposes (figure 2) and can be used in relation to the aircraft. It is obvious that the CG has to lie between these two limits in order to be balanced. The concept of MAC is used by aircraft designers when they determine stability characteristics of the aircraft.

Weight and Balance / Loadsheet - Aircraft MAC
Figure 1: Typical Mean Aerodynamic Chord

Weight and Balance / Loadsheet - Aircraft MAC
Figure 2: MAC in relation to the aircraft