TABLE OF CONTENTS 1. Introduction 2. The Composition of Aeroplane Weight 3. The Calculation of Aircraft Weight 4. Weight and Balance Theory 5. Centre of Gravity Calculations 6. Adding, Removing and Repositioning Loads 7. The Mean Aerodynamic Chord 8. Structural Limitations 9. Manual and Computer Load/Trim Sheets 10. Joint Aviation Regulations11. The Weighing of Aeroplanes 12. Documentation 13. Definitions 14. CAP 696 - Loading Manual 1. Introduction 1. As a professional pilot you will deal with aircraft loading situations on every flying day of your working life. The course that you are about to embark upon considers the inter-relationship between aircraft loading and other related subjects (principally aircraft performance and flight planning), and the very important airmanship aspects of proper aircraft loading. In general (non- aircraft type specific) terms, the ways in which the centre of gravity of both unladen and laden aircraft can be determined and checked as being within safe limits will be discussed. As and when you are introduced to new aircraft types, both during your flight training and during your subsequent career, you will be taught the loading procedures which are specific to that particular aircraft type. 2. In the Aircraft Performance book the problem of determining the maximum permitted take- off weight for an aircraft in a given situation is addressed. The Flight Planning book addresses the determination of the maximum payload, which can be carried on a given flight. In Aircraft Loading the problems of distributing the load within the aircraft such that the resultant centre of gravity is, firstly, within the safe limits laid down for the aircraft and, secondly, positioned so as to enhance the efficient performance of the aircraft, are addressed. 3. The Joint Aviation Authority has the task of ensuring that all public transport aircraft, irrespective of size or number of engines, are operated to the highest possible level of safety. To discharge this commission the JAA periodically introduces legislation in the form of operating rules or regulations and minimum performance requirements, which are complementary. All public transport aircraft are divided into Classes in which the types have similar levels or performance. There is a set of rules and requirements for each Class of aeroplanes, which dictate the maximum mass at which an aeroplane may be operated during any particular phase of flight. 4. With the introduction of the Joint Aviation Authority syllabus the word ‘mass’ is used instead of the word ‘weight’. In all British and American publications, weight is still preferred and used to express the downward force exerted by mass. The reason the JAA use mass is because weight = mass x acceleration i.e. weight = mass x 1. Therefore weight and mass are synonymous. Throughout this book the word ‘weight’ has been used and may be exchanged for the word ‘mass’ if preferred. 5. In addition to this the metric system of measuring weight and volume is preferred by the JAA and it may be necessary to convert Imperial or American quantities to metric equivalents. If such is the case use the following method. Conversion between Weight and Volume 6. The weights and volumes obtained for the purpose of centre of gravity calculations are frequently given as a mixture of metric and imperial measures. For example a British or American built aircraft may well have its weights presented in the Aeroplane Flight Manual (AFM) in pounds and when loaded on the continent the load may be quoted in kilograms. Fuel is delivered in litres, imperial gallons or US gallons, but of course must figure in the load sheet calculations in pounds or kilograms. Although the conversion between differing units of weight and volume, and indeed the conversion between volume and weight for fluids with a given specific gravity, is covered elsewhere in the course, the following paragraphs are included in this manual for your guidance. 7. To convert a volume of liquid to weight and vice versa the density of the liquid must be considered. The density is expressed as a specific gravity (SG). 1 litre of pure water weighs 1 kg and 1 imperial gallon pure water weights 10 lb. The SG of pure water is taken as the datum SG of 1.0. 8. When converting litres of any liquid to kilograms the volume must be multiplied by the specific gravity, or when converting kilograms to litres the weight must be divided by the specific gravity. Similarly, when converting imperial gallons to pounds the volume must be multiplied by (10 x the specific gravity), or to convert pounds to imperial gallons the volume must be divided by (10 x the specific gravity) of the liquid. 9. Aviation fuels and oils are lighter than pure water, therefore their specific gravities will be less than 1.0. 10. The diagram at Figure 0-1 may help you with these conversions. When using the diagram at Figure 0-1 and moving in the direction of the arrows, multiply (as shown). Conversely, when moving in the opposite direction, divide. Volume Conversions 11. In some problems the oil is measured in quarts. They may be in Imperial measurements or American. It does not matter, the conversion is the same as shown below in Paragraph 12. 12. 2 Pints = 1 Quart 4 Quarts = 1 Gallon 8 Pints = 1 Gallon 13. When travelling in the direction of the arrows multiply, when travelling in the opposite direction divide. 2. The Composition of Aeroplane Weight Weight Limitations 1. The Composition of Aeroplane Weight 1. The total weight of an aeroplane is the weight of the aeroplane and everyone and everything carried on it or in it. Total weight comprises three elements, the basic weight, the variable load and the disposable load. Basic Weight. This is the aeroplane weight plus basic equipment, unusable fuel and undrainable oil. Basic equipment is that which is common to all roles plus unconsumable fluids such as hydraulic fluid. Variable Load. This includes the role equipment, the crew and the crew baggage. Role equipment is that which is required to complete a specific tasks such as seats, toilets and galley for the passenger role or roller convey or, lashing points and tie down equipment for the freight role. Disposable Load. The traffic load plus usable fuel and consumable fluids. The traffic load is the total weight of passengers, baggage and cargo, including any non-revenue load. The disposable load is sometimes referred to as the useful load. 2. Although these are the weight definitions used in the load sheet there are other terms which are commonly used. These are: Absolute Traffic Load. The maximum traffic load that may be carried in any circumstances. It is a limitation caused by the stress limitation of the airframe and is equal to the maximum zero fuel weight minus the aircraft prepared for service weight. All Up Weight (AUW). The total weight of an aircraft and all of its contents at a specific time. Design Minimum Weight. The lowest weight at which an aeroplane complies with the structural requirements for its own safety. Dry Operating Weight. The total weight of the aeroplane for a specific type of operation excluding all usable fuel and traffic loads. It includes such items as crew, crew baggage, catering equipment, removable passenger service equipment, and potable water and lavatory chemicals. The items to be included are decided by the Operator. The dry operating weight is sometimes referred to as the Aircraft Prepared for Service (APS) weight. The traffic load is the total weight of passengers, baggage and cargo including non-revenue load. [JAR-OPS 1.607 (a)]. Empty Weight. (Standard Empty Weight) The weight of the aircraft excluding usable fuel, crew and traffic load but including fixed ballast, engine oil, engine coolants (if applicable) and all hydraulic fluid and all other fluids required for normal operation and aircraft systems, except potable water, lavatory pre-charge water and fluids intended for injection into the engine (de- mineralised water or water-methanol used for thrust augmentation). Landing Weight. The gross weight of the aeroplane, including all of its contents, at the time of landing. Maximum Ramp Weight. The maximum weight at which an aircraft may commence taxiing and its equal to the maximum take-off weight plus taxi fuel and run-up fuel. It must not exceed the surface load bearing strength. Maximum Structural Landing Weight. The maximum permissible total aeroplane weight on landing in normal circumstances. [JAR-OPS 1.607 (c)]. Maximum Structural Take-Off Weight. The maximum permissible total aeroplane weight at the start of the take-off run. [JAR-OPS 1.607 (d)]. Maximum Total Weight Authorised (MTWA). The maximum total weight of aircraft prepared for service, the crew (unless already included in the APS weight), passengers, baggage and cargo at which the aircraft may take-off anywhere in the world, in the most favourable circumstances in accordance with the Certificate of Airworthiness in force in respect of aircraft. Maximum Zero Fuel Weight. The maximum permissible weight of an aeroplane with no usable fuel. The weight of fuel contained in particular tanks must be included in the zero fuel mass when it is explicitly mentioned in the Aeroplane Flight Manual limitations. This is a structural limitation imposed to ensure that the airframe is not overstressed. [JAR-OPS 1.607 (b)]. Payload. Anyone or anything on board the aeroplane the carriage of which is paid for any someone other than the operation. In other words anything or anyone carried that earns money for the airline. Total Loaded Weight. The sum of the aircraft basic weight, the variable load and disposable load. Traffic Load. The total mass of passengers, baggage and cargo, including any non-revenue load. [JAR-OPS 1.607 (f)]. Zero Fuel Weight. This is the dry operating weight plus the traffic load. In other words it is the weight of the aeroplane without the weight of usable fuel. Equipment Ballast. Additional fixed weights which can be removed, if necessary, that are carried, to ensure the centre of gravity remains within the safe limits, in certain circumstances. Basic Equipment. The unconsumable fluids and the equipment which is common to all roles for which the operator intends to use the aircraft. Load Spreader. A mechanical device inserted between the cargo and the aircraft floor to distribute the weight evenly over a greater floor area. Unusable Fuel. That part of the fuel carried which is impossible to use because of the shape or position of particular tanks. Unusable Oil. That part of the oil lubrication system that cannot be removed due to the construction of the system. 3. The total weight of an aeroplane comprises many different components, all of which, together with the appropriate lever arms, are recorded in the weight and CG Schedule. 4. The standard empty weight of the aeroplane is the weight of the aircraft excluding the usable fuel, the crew and the traffic load but including any fixed ballast, unusable fuel, all engine coolant and all hydraulic fluid. 5. The basic weight of an aeroplane is essentially the empty weight plus the weight of basic equipment, that is equipment which is common to all roles in which the aircraft may be required to perform. The basic weight and the corresponding CG position, together with the declared basic equipment showing the weight and arm of each item, are shown in Part A of the Weight and CG Schedule or in the Loading and Distribution Schedule as appropriate. 6. To equip an aircraft to perform a particular role it may be necessary to fit additional equipment. This is known as role equipment, an example would be the passenger seats, toilets and galleys, which may vary in quantity for a large public transport aircraft. 7. The role equipment (variable load) detailed in Part B may be for as many roles as the operator wishes, but for every role the weights and moments must be stated. The weight and moment of the crew is included in Part B. Under certain circumstances, standard crew (and passenger) weights are assumed, otherwise the weight of each crew member must be determined by weighing. The occasions on which standard weights may be used are discussed in the Chapter entitled ‘Joint Airworthiness Requirements’. 8. With the role equipment fitted the aircraft is ready to enter service. The weight of the aircraft in this condition is called the Aircraft Prepared for Service (APS) weight, or the Dry Operating Weight (DOW). The total weight of the aeroplane comprises the APS weight plus the disposable load, which is made up of usable fuel and the payload. 9. Details of the disposable load must be entered in Part C of the Weight and CG Schedule, which contains the lever arm of each cargo stowage position, hold and each row of passenger seats. Full details of all fuel and oil tanks are also included in this part of the Schedule stating the arm, maximum capacity and weight when full for aircraft exceeding an MTWA of 2730 kg. 10. For an aircraft having a valid Certificate of Airworthiness a valid Weight and CG Schedule must be completed every time the aircraft is weighed. Each Schedule must be preserved for a period of six months following the subsequent re-weighing of the aircraft. 11. If the person who is the operator ceases to be the operator, he (or his representative if he dies) must retain the Schedule or pass it on to the new operator for retention for the requisite period. Weight Limitations 12. The factors which may limit the maximum Take-Off Weight (TOW) are: The Structural Limits. These are weight limits, which are imposed by the manufacturer, and agreed by the Authority, to ensure the aeroplane is not over-stressed. These structural weights include the maximum structural ramp weight, the maximum structural take-off weight, the maximum zero fuel weight and the maximum structural landing weight. The Field-Length Limited Take-Off Weight. This is the TOW as limited by the available field lengths and the prevailing meteorological conditions at the departure aerodrome. The Weight-Altitude-Temperature (WAT) Limit. This limitation is imposed on TOW by minimum climb gradient requirements, which are specified in Joint Airworthiness Requirements The En-Route Requirements. The weight of the aircraft at any stage of the flight en-route must be such that the aircraft can safely clear any objects within a specified distance of the aircraft’s intended track. Depending on the aircraft’s performance category, the loss of power from a specified number of engines will be assumed when determining the maximum weight at which the aircraft can safely clear en-route obstacles. En-route terrain clearance may impose a limitation on the take-off weight. The Maximum Landing Weight. This may be dictated by the structural limitation, the Field- Length Limit or the WAT Limit at the destination or alternate aerodromes. The Maximum Take-off Weight. The lowest restricted weight of the field-length limitation, the WAT limitation and the structural limitation is the maximum TOW. 13. As already discussed, the disposable load consists of the usable fuel and the traffic load. In order that the maximum traffic load can be carried it may be necessary to limit the amount of fuel which is carried to a safe minimum. Whether or not the fuel carried actually limits the traffic load, it is normally prudent to reduce the fuel load to a safe minimum in order to reduce the all up weight of the aircraft. This will result in lower operating costs, higher cruise levels, reduced thrust take-offs and/or easier compliance with noise abatement procedures on take-off. The total fuel required on any particular flight comprise the following: Route Fuel. This is the fuel used from departure to destination aerodromes and may be minimised by operating at the most economical pressure altitude accounting for the temperature and wind component, but not below the minimum safe altitude. Diversion Fuel. The fuel required to proceed from the destination to the alternate aerodrome in the prevailing conditions. Holding Allowance. The fuel required to enable the aircraft to hold at a specified pressure altitude and for a specified period of time. Contingency Allowance. An amount of fuel carried to counter any disadvantage suffered because of unforecast adverse conditions. Landing Allowance. The fuel required to be used from overhead the landing aerodrome to the end of the landing roll. 14. On occasions it is advantageous to carry more than the minimum fuel for a given sector. The obvious example is when fuel will not be available at the destination aerodrome. Alternatively, the cost of fuel at the destination aerodrome may be so high that the cost differential (departure aerodrome fuel cost versus destination aerodrome fuel cost) may be so great that it is cheaper to carry the fuel for the return or subsequent sector outbound from the original departure aerodrome. In either event, when this is done the first sector would be termed a ‘Tankering Sector’. 15. The size of the traffic load may be restricted by reasons other than the disposable load which is available once the fuel load has been decided. It may be impossible to distribute the traffic load such that the centre of gravity of the laden aircraft remains within the safe specified limits, in which case some of the traffic load may have to be off-loaded. Floor loading factors may have to be considered. With a payload which is light in weight but bulky it may be physically impossible to fit the traffic load into the aircraft. Operating Overweight 16. A safely loaded aircraft is one in which the total weight of traffic load is equal to or less than the maximum permissible traffic load for a given flight and the distribution of that traffic load is such that the centre of gravity of the laden aircraft lies within the fore and aft limits of centre of gravity which are permitted for that aircraft operating in the specified role. 17. The effects of operating in an overweight condition include: (a) Reduced acceleration on the ground run for take-off. The take-off speeds are increased because of the weight, and this results in an increased take-off run required and an increased take-off distance required. (b) Decreased gradient and rate of climb which decreases obstacle clearance capability after take-off and the ability to comply with the minimum climb gradient requirements. (c) Increased take-off speeds impose a higher load on the undercarriage and increased tyre and wheel temperatures. Together these reduce the aeroplane’s ability to stop rapidly in the event of an abandoned take-off. (d) Increased stalling speed which reduces the safety margins. (e) Reduced cruise ceiling which increases the fuel consumption resulting in a decreased operational range. It may also cause en-route terrain clearance problems. (f) Impaired manoeuvrability and controllability. (g) Increased approach and landing speeds causing a longer landing distance, landing ground run, increased tyre and wheel temperatures and reduced braking effectiveness. (h) Reduced one-engine inoperative performance on multi-engined aircraft. (i) Reduced structural strength safety martins with the possibility of overstressing the airframe. 18. In addition to ensuring that the maximum permissible all-up weight of an aircraft is not exceeded it is of vital importance to ensure that the distribution of the permissible weight is such that the balance of the aircraft is not upset.