Lubricants and fuels.pdf

Lubricating Oil Aircraft Engine Oils The properties and characteristics of lubricating oils vary with the oil type. Oil with the correct specifications must always be used in each engine because the wrong oil could lead to damaged or failed engine components. With that caution in mind...

Lubricating Oil Aircraft Engine Oils The properties and characteristics of lubricating oils vary with the oil type. Oil with the correct specifications must always be used in each engine because the wrong oil could lead to damaged or failed engine components. With that caution in mind, consider the following discussion on oil properties and the various oil types. Typical applications of the different oil types are discussed, as well as the methods used to grade aircraft engine oils. The correct oil specification for an engine type can be found in the following: Aircraft Operator’s Manual Aircraft Maintenance Manual Engine Maintenance Manual Engine oil tank service placard. Oils with different specifications and brand name must never be mixed. Lubricating oil 2022-08-08 B1-15b Gas Turbine Engine Page 12 of 291 CASA Part 66 - Training Materials Only  Lubrication The primary purpose of a lubricant is to reduce friction between moving parts and to help cool engine bearings. It is also used to seal, and cushion moving parts, clean the engine interior, and protect against corrosion. Since engines require a lubricant which can circulate freely, liquid lubricants such as oils are the most widely used in aircraft engines. Many of the metal parts inside an aircraft engine have surfaces which appear smooth to the naked eye. However, if you were to microscopically examine those same parts, you would see a rather rough surface consisting of several peaks and valleys. When those engine parts rub against one another, the resulting friction soon wears away the metal. To reduce this friction, a film of lubrication oil is placed between the moving parts. A film of lubrication oil prevents contact between moving parts Oil wets the surfaces, fills in the valleys, and holds the metal surfaces apart as long as the oil film remains unbroken. The engine parts then slide over each other on a film of oil rather than grind together. Therefore, friction is reduced, and part wear is minimised. The amount of clearance between moving parts is a determining factor when choosing the proper type and grade of oil. Oil must adhere to a part sufficiently and be thick enough to provide an adequate protective film that will not break down and allow metal-to-metal contact. 2022-08-08 B1-15b Gas Turbine Engine Page 13 of 291 CASA Part 66 - Training Materials Only  Heat Absorption In addition to reducing friction and wear, oil absorbs some of the heat produced by combustion as it circulates through the engine. The turbine bearings are especially dependent on lubricating oil for cooling. However, once the oil heats up, a means of cooling the oil must be provided. Therefore, several engine lubrication systems contain an oil cooler. An oil cooler is basically a heat exchanger that transfers the heat contained in the oil to the outside air or to fuel. Fuel/oil heat exchanger and air/oil cooler Cushioning Oil also provides a cushioning effect between metal parts. For example, the thin film of oil between gear bushing absorbs some of the hammering shock from the meshed gears action. The cushioning action also helps reduce some of the impact force between shafts and their bearings. The oil film cushions contact between gears 2022-08-08 B1-15b Gas Turbine Engine Page 14 of 291 CASA Part 66 - Training Materials Only  Cleaning The oil in a lubrication system also reduces engine wear by serving as a cleaning agent. As the oil circulates, it picks up foreign particles such as dirt, dust, carbon, and small amounts of water. These particles are held in suspension by the oil and carried to a filter where they are trapped and removed. Cleaning 2022-08-08 B1-15b Gas Turbine Engine Page 15 of 291 CASA Part 66 - Training Materials Only  Corrosion Protection Metal engine parts which are exposed to moist air and various chemicals tend to rust or form other types of surface corrosion. This is especially true for parts which have been hardened by nitriding. The oil film which coats the internal engine parts acts as a barrier, preventing oxygen and moisture from reaching the metal surface and causing it to corrode. Bearing corrosion 2022-08-08 B1-15b Gas Turbine Engine Page 16 of 291 CASA Part 66 - Training Materials Only  Aircraft Lubricating Oil Oil Characteristics (Synthetic) Because of the high temperature required in the operation of gas turbine engines, it became necessary for the industry to develop lubricants which would retain their characteristics at temperatures that cause petroleum lubricants to evaporate and break down into heavy hydrocarbons. Synthetic lubricants do not evaporate or break down easily, reducing coking, lacquers, and other deposits. Synthetic, rather than petroleum-based, lubricants are used in turbine engines. The desirable characteristics of synthetic oils are as follows: Low volatility – to prevent evaporation at high altitudes. Anti-foaming quality – for more positive lubrication. Low lacquer and coke deposits – keeps solid particle formation to a minimum. Low pour point – the lowest temperature at which oil flows by gravity Excellent film strength qualities of cohesion and adhesion – a characteristic of oil molecules that allows them to stick together under compression loads and stick to surfaces under centrifugal loads High flash point – the temperature at which oil when heated gives off flammable vapours that will ignite if near a flame source Low viscosity – oil properties do not change over a wide temperature range – in the order of -40 °C to + 204 °C. High viscosity index – meaning the oil will tend to retain its viscosity when heated to its operating temperature. Low Volatility Volatility in chemistry is a measure of the speed at which a chemical element or chemical compound evaporates. Higher volatility indicates faster evaporation, and a lower volatility means it will evaporate slower. Oil must have a low evaporation rate to accomplish any cooling from circulation. Gas turbine engine synthetic lubricants have a low evaporation rate. Therefore, they have low volatility. 2022-08-08 B1-15b Gas Turbine Engine Page 17 of 291 CASA Part 66 - Training Materials Only  Anti-Foaming High flow rates, spray jets and the introduction of pressurising and vent air, can cause oil foaming. Foaming will cause an increase in volume and reduce lubricating qualities and cause lube and scavenge pump cavitation. Gas turbine engine synthetic oils have additives to prevent foaming, reduce cavitation and maintain positive lubrication. Oil foaming Low Coke and Lacquer Deposits As a gas turbine engine ages, internal clearances increase allowing excessive air leakage into oil wetted areas. This results in excessive oxidation, viscosity increase, or even sludge formation in the oil. Coke, carbon, and lacquer may also build up in oil under high temperatures and pressures. These become solid particle contaminants that can damage or block components or filters. These deposits should not be confused with normal oil discolouration which will be discussed later. Low coke and lacquer deposits 2022-08-08 B1-15b Gas Turbine Engine Page 18 of 291 CASA Part 66 - Training Materials Only  Low Pour Point Pour point is the lowest temperature at which oil will still flow due to gravity. Generally, pour point should be below the minimum ambient temperature for engine starting. To ensure oil circulation in extremely cold conditions, engine/oil heating may be required before starting is attempted. For these reasons a multi-viscosity oil must be used. Gas turbine engine synthetic oils operate in a temperature range of –40 °C to + 204 °C (Mobil Jet Oil 2). Pour point 2022-08-08 B1-15b Gas Turbine Engine Page 19 of 291 CASA Part 66 - Training Materials Only  High Film Strength Film strength refers to the amount of pressure required to force out a film of oil from between two pieces of flat metal. The higher the film strength, the more protection is provided to parts such as splash lubricated gear and bearings, wherever the lubricant is not under oil system pressure. Synthetics routinely exhibit a nominal film strength of well over 3,000 psi, while petroleum oils average somewhat less than 500 psi. The result is more lubricant protection between moving parts with synthetics. Achieving high film strength oil within the optimum viscosity range is quite difficult. High film strength is required to prevent the film of oil from being forced out between moving parts. Although it is not easy to measure this film strength directly; it is best understood through demonstration. High film strength will give a smooth, slippery feel when the oil is rubbed rapidly between the fingers. High film strength 2022-08-08 B1-15b Gas Turbine Engine Page 20 of 291 CASA Part 66 - Training Materials Only  High Flash Point The flash point is the temperature at which oil gives off flammable vapours. Oil which gives off flammable vapours at low temperature has a low flash point. A high flash point means that the oil must be heated to a high temperature to give off vapours (higher flash point = lower fire risk). Generally, gas turbine engine synthetic oils have a flash point above 250 °C. High flash point 2022-08-08 B1-15b Gas Turbine Engine Page 21 of 291 CASA Part 66 - Training Materials Only  Low Viscosity Viscosity is defined as the oil’s resistance to flow, or its pourability. Viscosity of a lubricating oil is very dependent on the temperatures experienced. The oil must be light enough to circulate freely, yet heavy enough to provide the proper oil lubricating film at normal engine operating temperatures. Oil that flows freely has a low viscosity. Oil that flows slowly is viscous or has a high viscosity. Low viscosity High viscosity 2022-08-08 B1-15b Gas Turbine Engine Page 22 of 291 CASA Part 66 - Training Materials Only  Viscosity Index The viscosity index (V.I.) of oil is a number that indicates the effect of temperature changes on the viscosity of the oil. A low V.I. signifies a relatively large change of viscosity with changes of temperature. In other words, the oil becomes extremely thin at high temperatures and extremely thick at low temperatures. On the other hand, a high V.I. signifies relatively little change in viscosity over a wide temperature range. The viscosity index is determined by measuring the viscosity change when a liquid lubricant is heated to two different temperatures. An important quality of synthetic lubricants is determined in this way. Synthetic Oil Properties Theoretically, the perfect engine oil is thin enough to circulate freely, yet heavy enough to stay in place and maintain reasonable film strength. However, in practice, a compromise must be made, and several factors must be considered in determining the proper grade of oil to use in a particular engine. Some of these factors include engine operating loads, rotational speeds of bearings, and operating temperatures. When determining the proper grade of oil to use there are several properties which must be considered. 2022-08-08 B1-15b Gas Turbine Engine Page 23 of 291 CASA Part 66 - Training Materials Only  Gas Turbine Engine Lubricating Oil Gas turbine engine oil must have a high enough viscosity for good load carrying ability, but it must also be of sufficient low viscosity to provide good flow ability. Because of these requirements, synthetic, rather than petroleum-based, lubricants are used in turbine engines. Synthetic oils are man-made (synthesised) from extracts of mineral, vegetable, and animal oils. The blending of these oils with suitable chemicals in different amounts produces a lubricant, which meets a prescribed specification of the petroleum industry and the aviation industry. Synthetic oils are not compatible with and cannot be mixed with mineral-based oils. In addition, most manufactures recommend that different brands or types of synthetic oils not be mixed. Synthetic oils provide lubrication over a wide temperature range (multi-viscosity) and reduce carbon and coke build up, and they have a low internal friction and a high resistance to thermal breakdown. There are currently three types of synthetic oils in use: Type I. MIL-Pref-7808 Type II. MIL-Pref-23699 Type II 3rd Generation. MIL-PRF-23699-HTS (High Thermal Stability) Do not mix Type I with Type II oils. Mixing of brands of Type II oil is not recommended due to possible incompatibility of additives. Gas turbine engine lubricating oil Synthetic oils of Type I and II are straw-coloured when new but darken over time in service. Type-II 3rd Gen synthetic oil is slightly darker when new. 2022-08-08 B1-15b Gas Turbine Engine Page 24 of 291 CASA Part 66 - Training Materials Only  The colour change comes from an oxidation inhibitor added to the oil that darkens after coming in contact with oxygen. The gradual darkening effect is not an indication of oil degradation but rather the inhibitor performing its function of absorbing oxygen contained in the air that is normally present in main bearing compartments and gearboxes. If there is excessive oxidation in the oil you may get a viscosity increase or even sludge formation in the oil. The gradual darkening effect - light The gradual darkening effect - dark 2022-08-08 B1-15b Gas Turbine Engine Page 25 of 291 CASA Part 66 - Training Materials Only  Oil Consumption In the performance of all the previously mentioned functions, a portion of the lubrication oil is consumed. The amount of oil consumed depends on several factors such as engine rpm, engine temperature, operating clearances, and lubricant characteristics. Generally, higher rpm and temperatures, larger clearances, and less viscosity correspond to higher consumption rates. Engine oil service 2022-08-08 B1-15b Gas Turbine Engine Page 26 of 291 CASA Part 66 - Training Materials Only  Oil Handling (Warnings and Cautions) Warning Synthetic oils contain additives which are readily absorbed by the skin and may be considered hazardous. Read the SDS and use your PPE. Caution 1. Never use silicon-based grease to lubricate oil system O-rings. Such grease will contaminate the engine oil - follow the manufacturer’s instructions. 2. Synthetic oils will stain clothes and can damage paints and electrical insulations – clean up spills immediately. © Aviation Australia Oil handling precautions 2022-08-08 B1-15b Gas Turbine Engine Page 27 of 291 CASA Part 66 - Training Materials Only  Turbine Engine Fuels Turbine Engine Fuels (Jet Fuel) Jet fuels are liquid hydrocarbons similar to kerosene (some blended with gasoline for mainly military use). Hydrocarbon fuel is a compound of hydrogen and carbon found in coal, natural, and crude oil. This mixture is designed to freely mix with oxygen at combustion flow rates and temperatures. The blending of gasoline reduces the fuel’s tendency to become too viscous due to extremely low temperatures at high altitudes. This is a problem which affects performance of some very high- altitude aircraft. The oxides which are formed by combustion in a gas turbine engine are mostly gases. This is another quality designed into jet fuels which keeps solid particles to minimum, solids that would impinge on turbine nozzle vanes and turbine blades causing erosion. Jet fuels are not coloured for identification as are reciprocating engine fuels, but from time to time they do have a natural light straw colour. Aviation Australia Fuel sampling 2022-08-08 B1-15b Gas Turbine Engine Page 28 of 291 CASA Part 66 - Training Materials Only  Wide-Cut Fuels Wide-cut fuel is a hydrocarbon mixture spanning the gasoline and kerosene boiling ranges. JET B is the most common wide-cut fuel in use today and is known in some parts of the world as AVTAG. It is still used by commercial operators operating in and out of very cold climates and by the military. However, compared to a kerosene-type fuel, wide-cut jet fuel was found to have operational disadvantages due to its higher volatility: Greater losses due to evaporation at high altitudes. Greater risk of fire during handling on the ground. Crashes of planes fuelled with wide-cut fuel were less survivable. A94-946 aircraft 2022-08-08 B1-15b Gas Turbine Engine Page 29 of 291 CASA Part 66 - Training Materials Only  Commercial Aviation Turbine Fuels When the commercial jet industry was developing in the 1950s, kerosene-type fuel was chosen as having the best combinations of properties. The most common jet fuels currently in use are: JET A-1 (Used worldwide, except in the USA) JET A (Used in the USA). The important difference between the two fuels is that JET A-1 has a lower maximum freezing point than Jet A (JET A: –40 °C, JET A-1: –47 °C). The lower freezing point makes Jet A-1 more suitable for long international flights, especially on polar routes during the winter. The terms AVTAG and AVTUR only refer to the category of fuel, i.e., AVTAG – wide-cut fuel or AVTUR kerosene-based aviation turbine fuel, these terms DO NOT identify the type or the specification of fuel. Jet A-1 is used worldwide as aviation turbine fuel 2022-08-08 B1-15b Gas Turbine Engine Page 30 of 291 CASA Part 66 - Training Materials Only  Fuel Recognition Unlike the various grades of reciprocating engine fuels that are dyed different colours to aid in recognition, all turbine fuels are either colourless or have a light straw colour. An off-colour may indicate an unapproved turbine fuel which does not meet specifications. Therefore, you should avoid using these fuels unless their suitability for aircraft use can be verified. Approved turbine fuels are identified by white letters on a black background. In addition, valves, loading and unloading connections, switches, and other control equipment are colour-coded according to the type of fuel they dispense. The fuel in piping is identified by name and by coloured bands painted or decaled around the pipe at intervals along its length. Fuel types are identified by coloured banding, either black for JET A, grey for JET A-1 or yellow for JET B. Fuel colour codes 2022-08-08 B1-15b Gas Turbine Engine Page 31 of 291 CASA Part 66 - Training Materials Only  Specific Gravity Specific gravity is defined as: The density of a volume of fuel compared to the same volume of pure water at the same temperature With water at a value of 1, the SG of JET A-1 is 0.8 (nominally) and AVGAS is 0.72 (nominally). Therefore calorific value per Litre of JET A-1 will be greater. As fuel tanks are a set volume in aircraft, then JET A-1 gives more heat energy for a given tank capacity. However, the volume of fuel changes with changes in temperature. That is, 1 litre of JET A-1 at 30 °C weighs less than 1 litre at 15 °C. Therefore, SG becomes critical when calculating large fuel uplifts. Specific gravity 2022-08-08 B1-15b Gas Turbine Engine Page 32 of 291 CASA Part 66 - Training Materials Only  Fuel Weight with Change in Density (S.G.) Specific Gravity Full Tanks 203, 475 litres 0.780 158, 710 kgs 0.785 159, 278 kgs 0.790 160, 745 kgs 0.795 161, 798 kgs 0.800 162, 780 kgs 0.805 163, 797 kgs The table shows the maximum fuel load weight with increases in specific gravity between S.G 0.780 and 0.805, an increase of 5087 kg (over five tons). 2022-08-08 B1-15b Gas Turbine Engine Page 33 of 291 CASA Part 66 - Training Materials Only  Fuel Volatility High volatile fuels (the ability to vaporise or evaporate) have both advantages and disadvantages. An advantage is that it enhances combustion, cold starting and in-flight re-lights. Disadvantages are: Fire hazard Vapour locks Fuel loss through evaporation. Wide-cut fuels were extremely volatile – hence their limited use. Modern fuels are less volatile but two critical factors remain. Flash point - the temperature at which ignitable vapours are produced. Vapour pressure - the pressure required (acting on the surface of fuel) to prevent dangerous vapours developing. High vapour pressure indicates a fire risk and excessive fuel loss through vaporisation at altitude, especially if the aircraft climbs quickly and the fuel temperature does not cool before being exposed to low ambient pressure. Fire hazard 2022-08-08 B1-15b Gas Turbine Engine Page 34 of 291 CASA Part 66 - Training Materials Only  Vapour Pressure Vapour pressure is the amount of pressure that needs to be applied to the surface of the fuel to prevent vaporising. Hence, fuel tanks have a National Advisory Committee for Aeronautics (NACA) scoop under the wings to provide a small head of pressure on the fuel. This pressure also aids priming the boost pumps. High vapour pressure means the fuel needs a high tank pressure to stop vaporisation, especially if the fuel is warm and the aircraft climbs rapidly, then the ambient pressure would be low, and a lot of fuel vapour will disappear out the vent system. NACA scoop If the vapour pressure is too low, the fuel will not vaporise properly and cause starting problems. If the vapour pressure is too high, the fuel will turn to vapour in the fuel lines and cause vapour locks at the Fuel Control Unit (FCU). For example: JET A-1 requires between 0.1 to 0.5 psi and AVGAS about 7 psi. Vapour pressure is related to flash point. The lower the flash point the higher the vapour pressure needed. 2022-08-08 B1-15b Gas Turbine Engine Page 35 of 291 CASA Part 66 - Training Materials Only  Flash Point Flash point - the temperature at which fuel gives off ignitable vapours. The higher the flash point, the lower the fire hazard. Typical values are: JET A-1 38 °C AVGAS -40 °C In the event of a fuel spill, more ignitable vapour would be present about an aircraft fuelled with AVGAS than JET A-1. The degree of fire risk is therefore related to flash point and vapour pressure of fuel. Flash point 2022-08-08 B1-15b Gas Turbine Engine Page 36 of 291 CASA Part 66 - Training Materials Only  Fuel Management and Safety Precautions Fuel Contamination Contaminants are all forms of foreign material. Water is just one. The easiest and most common method to find contaminants is to drain the fuel into a clear glass container and examine it. Allow time for the water to settle out then test for free water by visual inspection or with a water detecting process. Because oil and hydraulic fluids readily dissolve in fuel, detection can be almost impossible. Although, it may sometimes be detectable by smell. Fuel contamination Swarf from internal tank repairs, maintenance and modifications can clog boost pump inlet screens and fuel system filters. Swarf is a common source of contamination. It is important to clean up after the job is finished. 2022-08-08 B1-15b Gas Turbine Engine Page 37 of 291 CASA Part 66 - Training Materials Only  Water Contamination of Fuel Aviation turbine fuel is hydroscopic; therefore, water is always present due to condensation in aircraft and supplier tanks. Water is present in two forms: Dissolved: Water in complete solution that cannot be detected visually and does not affect engine operation. Free: Water is suspended water or entrained water (coloured blue for clarity) Because of water’s higher S.G. the water settles at the lowest point, somewhere near the boost pump inlet. There are only two types of water, ‘dissolved’ and ‘free’ – ‘suspended’ water is a form of free water. Free water can form into ice and be detrimental to engine operations in sufficient quantity. Aircraft tanks are routinely checked before the first flight of the day, after settling out time, and before fuelling. Fuel samples are taken from the aircraft fuel tank drain valves. Settled free water is easily detected even in clear JET A-1 – you will notice a dividing line between the fuel and water. Suspended or entrained water can be checked with the shell water detection caps or with a water finding paste. Because of water's higher S.G., the water settles at the lowest point One particular paste will turn from green to grey to vivid purple when water is present. The paste is usually used to check underground tanks by putting it on the bottom of a dip stick. Refuelling company personnel will check the quality of fuel as it is delivered to the aircraft using detector kit. 2022-08-08 B1-15b Gas Turbine Engine Page 38 of 291 CASA Part 66 - Training Materials Only  Shell detector kit and water finding paste Another problem with water contamination is the risk of corrosion. This can be caused directly by the presence of water, or indirectly by the moisture causing microbial growth and then electrolytic corrosion. Fuel system components are made from corrosion-resistant material that also provides a protective coating. Corrosion can also be addressed through regular maintenance programs and the use of fuel additives. The main problem with water in turbine engine fuel is that it may serve as a home for microscopic- sized animal and plant life. Microbial growth, or contamination with bacteria, or ‘bugs,” has become a critical problem in some turbine fuel systems and some aircraft. Because microbes thrive in water, a simple and effective method to prevent or retard their growth is to eliminate the water. Sometimes microbial growth occurs despite efforts to eliminate water from the fuel tanks. 2022-08-08 B1-15b Gas Turbine Engine Page 39 of 291 CASA Part 66 - Training Materials Only  Microbial growth 2022-08-08 B1-15b Gas Turbine Engine Page 40 of 291 CASA Part 66 - Training Materials Only  Fuel Additives The most common fuel additives are the anti-icing and anti-microbiocidal agents. Anti-icing additives keep entrained water from freeze-up without the use of fuel heat, except at very low temperatures. The manufacturer’s manual will state the temperature at which fuel heat must be applied. Microbiocidal agents kill microbes, fungi, and bacteria which form slime, and in some cases matted waste in fuel systems. Most often the additives are premixed in the fuel-by-fuel distribution company. If it is not, the service person must add the agents when fuelling the aircraft. Most manufacturers of these products recommend their use year-round. Aviation fuel additives are compounds added to the fuel in very small quantities, usually measurable only in parts per million, to provide special or improved qualities. The quantity to be added and approval for its use in various grades of fuel is strictly controlled by the appropriate specifications. A few additives in common use are as follows: 1. Antioxidants prevent the formation of gum deposits on fuel system components caused by oxidation of the fuel in storage and inhibit the formation of peroxide compounds in certain jet fuels. 2. Static dissipater additives reduce the hazardous effects of static electricity generated by movement of fuel through modern high flow-rate fuel transfer systems. Static dissipater additives do not reduce the need for `bonding' to ensure electrical continuity between metal components (e.g. aircraft and fuelling equipment) nor do they influence hazards from lightning strikes. 3. Corrosion inhibitors protect ferrous metals in fuel handling systems, such as pipelines and fuel storage tanks, from corrosion. Some corrosion inhibitors also improve the lubricating properties of certain jet fuels. 4. Fuel System Icing Inhibitors (anti-icing additives) reduce the freezing point of water precipitated from jet fuels due to cooling at high altitudes and prevent the formation of ice crystals which restrict the flow of fuel to the engine. This type of additive does not affect the freezing point of the fuel itself. Anti-icing additives can also provide some protection against microbiological growth in jet fuel. 5. Metal deactivators suppress the catalytic effect which some metals, particularly copper, have on fuel oxidation. 6. Biocide additives are sometimes used to combat microbiological growths in jet fuel, often by direct addition to aircraft tanks; as indicated above some anti-icing additives appear to possess biocidal properties. 2022-08-08 B1-15b Gas Turbine Engine Page 41 of 291 CASA Part 66 - Training Materials Only  Fuel Storage Fuel should be allowed to settle in storage tanks. Storage tanks should be constructed from stainless steel or aluminium to prevent rust and scale formation and suction lines must be positioned above the bottom of the tank, so sediment is not sucked out. Fuel pumped from storage tanks must be filtered to prevent aircraft tank contamination. Airport fuel storage tank Aircraft Refuelling Static electricity is produced during fuelling. To prevent arcing and potential explosion or fire, both the aircraft and fuel delivery unit must be grounded (earthed). Unit to the tarmac ground point Unit to the aircraft (designated aircraft earthing point). Refuel nozzle to aircraft (designated aircraft earthing point). Refuelling personnel must also earth themselves. Refuelling procedures 2022-08-08 B1-15b Gas Turbine Engine Page 42 of 291 CASA Part 66 - Training Materials Only