Engine Lubrication Systems PDF

Engine Lubrication Systems Engine Lubrication The primary function of the lubrication system is to supply oil to the various parts within the engine which are subjected to friction loads from engine rotation and heat loads from the gas path. Engine heat that radiates outwards is deal...

Engine Lubrication Systems Engine Lubrication The primary function of the lubrication system is to supply oil to the various parts within the engine which are subjected to friction loads from engine rotation and heat loads from the gas path. Engine heat that radiates outwards is dealt with by the nacelle ventilation system. Engine heat that radiates inwards is dealt with by the lubrication system. The oil is supplied under pressure along the main rotor shaft and to the gearboxes to reduce friction, to cool and to clean. It is then returned by a scavenging system to the oil storage tank to be used again and again. Oil consumption is low in gas turbine engines as compared to piston engines, and this accounts for the relatively small bulk oil storage tanks used. They can be as small as 3–5 L in capacity on business jet-sized engines and 20–30 L on large commercial type engines. The oil is not exposed to great quantities of combustion products and stays fairly clean by filtration. Heat, however, is a problem which can cause rapid oil decomposition, and for this reason temperature is carefully controlled by automatic cooling devices and carefully monitored by the engine operators. Two basic types of self-contained lubrication systems are used in today’s gas turbine engines: Pressure relief valve system Full flow system. The pressure relief valve system controls oil flow by limiting the pressure from the oil pump to a given value. In the full flow system, pressure changes with rpm, and this is the system of choice when the bearing vent cavities contain high air pressures. Both systems will be discussed in detail later. Engine lubrication systems can be classified as either of the following: Wet-sump system Dry-sump system. Oil Reservoir The purpose of the oil reservoir is to hold sufficient oil to allow for engine consumption at maximum flight operation and duration. 2022-08-08 B1-15b Gas Turbine Engine Page 46 of 291 CASA Part 66 - Training Materials Only  Wet-Sump Systems The oil supply for a wet-sump system is typically located in the main or accessory gearbox at the lowest point within the engine. From here, oil is pressurised and routed through multiple filters before reaching the main rotor bearings and couplings. It also allows splash lubrication to be used on accessory gears and bearings. Once the oil has lubricated the main bearings, it drains to low-lying areas, where scavenge pumps route it back to the sump or gearbox. Aviation Australia Wet-sump oil system Today, the majority of turbine engines use a dry-sump lubrication system consisting of pressure, scavenge and breather subsystems. 2022-08-08 B1-15b Gas Turbine Engine Page 47 of 291 CASA Part 66 - Training Materials Only  Dry-Sump Systems Dry-sump systems differ from wet-sump systems in that the oil is stored in a separate oil reservoir mounted either internally within the engine or externally on the engine or in the aircraft. In this type of system, an oil pump pulls oil from the oil reservoir and provides pressure and spray lubrication throughout the engine. The oil reservoir in a dry-sump system is usually constructed of sheet aluminium or stainless steel and is designed to furnish a constant supply of oil to the engine during all approved flight manoeuvres. They come in a variety of shapes and sizes, depending mainly on system requirements and the amount of space allowed around the engine when installed in the nacelle or airframe. System requirements also determine whether the tank is pressurised or unpressurised. Aviation Australia Dry-sump oil system Once circulated, the oil accumulates in low-lying areas, where scavenge pumps pick it up and pump it back to the reservoir. To ensure a positive flow of oil to the oil pump inlet, most oil reservoirs are pressurised. Pressurising the reservoir also helps to suppress oil foaming, which in turn prevents pump cavitation. In most cases, pressurisation is accomplished by installing an adjustable relief valve in the oil reservoir vent line. This way, reservoir pressure builds until the relief valve opens to relieve excess pressure. 2022-08-08 B1-15b Gas Turbine Engine Page 48 of 291 CASA Part 66 - Training Materials Only  © Aviation Australia Dry sump reservoir 2022-08-08 B1-15b Gas Turbine Engine Page 49 of 291 CASA Part 66 - Training Materials Only  Oil Reservoir Expansion Space All oil reservoirs have an expansion space of at least 10% of the tank capacity or 0.5 gal, whichever is greater. The expansion space provides sufficient room for oil to expand as it heats and allows room for the collection of foam. In addition, all oil filler caps or covers must be marked with the word OIL and the permissible oil designations. As an added feature, most of the oil reservoirs installed in some dry-sump systems include a scupper drain. Scupper drains catch spillage during servicing and overflows that may occur when the cap is opened. Aviation Australia Oil reservoir expansion space 2022-08-08 B1-15b Gas Turbine Engine Page 50 of 291 CASA Part 66 - Training Materials Only  Oil Separators As lubricating oil is agitated by an engine’s moving parts, air typically becomes entrained in the oil. To remedy this problem, many oil tanks contain some form of de-aerator or air-oil separator. In some engines, a separator may be installed in the accessory gearbox, while other systems rely on a separator in the oil reservoir. One type of de-aerator that may be installed in an oil system swirls the air/oil mixture, allowing centrifugal force to pull the oil from the air. Once the two are separated, the oil drains into the reservoir and the air is vented overboard. Another type of de-aerator consists of a tray in the top of the reservoir that the oil spreads out on when it is returned to the reservoir. As the oil spreads into a thin layer, entrapped air separates from the oil. Oil reservoir with de-aerator In oil reservoirs that are equipped with a dwell chamber, the oil/air mixture enters the dwell chamber at the bottom of the oil tank. Scavenge pump pressure then forces the oil upwards through the dwell chamber and spreads it into a thin film, facilitating the release of entrained air. 2022-08-08 B1-15b Gas Turbine Engine Page 51 of 291 CASA Part 66 - Training Materials Only  Aviation Australia Oil reservoir with dwell chamber Reservoir Oil Level The most common method of checking the oil level in the tank is with a dipstick. In lieu of a dipstick, some oil tanks incorporate a sight gauge for a visual means of checking oil level. However, these glass indicators tend to cloud over after prolonged use, and therefore many operators rely on the dipstick method. © Aviation Australia Oil reservoir dipstick and sight glass 2022-08-08 B1-15b Gas Turbine Engine Page 52 of 291 CASA Part 66 - Training Materials Only  Oil Pumps Oil Pump Categories Oil pumps can be classified under two categories: Pressure pumps Scavenge pumps. Oil pumps that are driven by the engine, as shown below, are called engine-driven pumps (EDPs). Engine driven pump Pressure pumps supply oil under pressure to the parts of the engine that require lubrication. Scavenge pumps return the oil from the lubrication points, after use, to the oil tank. Scavenge pumps are always larger in capacity than pressure pumps as the volume of the oil is increased because of expansion due to heat and trapped air bubbles in the oil. 2022-08-08 B1-15b Gas Turbine Engine Page 53 of 291 CASA Part 66 - Training Materials Only  Lubrication Pump Types Three of the more common types of oil pumps are: gear vane gerotor. The pumps connected to the pressure line and scavenge line can be of any given type. Gear Pumps A gear type pump consists of two steel gears, with one being driven by either the engine or some other power unit. The other gear meshes with, and is driven by, the drive gear. When the gears are rotated, oil is drawn into the pump, carried round between the teeth and the case, and delivered to the outlet side of the pump. In the illustration, the small arrows between the gear teeth show the path of the oil through the pump. Aviation Australia Gear type pump Gear pumps are used as pressure and scavenge pumps, and in some cases, the one pump may contain both pressure and scavenge elements. When both elements are contained in a single pump housing, the driven gears are on a common shaft. 2022-08-08 B1-15b Gas Turbine Engine Page 54 of 291 CASA Part 66 - Training Materials Only  The pressure element receives its supply from the oil tank, pressurises it and pumps it to the next component in the system, the oil filter. Similarly, the scavenge element receives oil from the main bearings and returns it to the oil tank. Gear pump (animated) - low pressure (blue) and high pressure (red) 2022-08-08 B1-15b Gas Turbine Engine Page 55 of 291 CASA Part 66 - Training Materials Only  Vane Pumps The vane pump consists of a rotor drive shaft, an eccentric (off-centre) rotor with sliding vanes though it which rotates as one piece. The space between the vanes and the case fills with oil as it passes the inlet and is carried towards the outlet. As the space near the outlet diminishes, the oil is forced out of the pump. The downstream resistance to the flow determines the oil pressure. Vane pumps are more tolerant of debris within the oil than are other types of pumps, and are lighter than the gear and gerotor types. Aviation Australia Vane type pump 2022-08-08 B1-15b Gas Turbine Engine Page 56 of 291 CASA Part 66 - Training Materials Only  Vane type pump (animated) 2022-08-08 B1-15b Gas Turbine Engine Page 57 of 291 CASA Part 66 - Training Materials Only  Gerotor Pumps A gerotor type pump uses a similar principle to the vane pump and consists of a lobe-shaped gear (not unlike the lobes on a camshaft) driven by the engine, a case and a rotor. The gear rides inside the rotor, which rotates freely within the housing. Using the illustration below, we can follow the operation of a gerotor pump. The six-toothed spur type drive gear is turned by an accessory drive from the engine, and as it turns, it rotates the seven‑toothed internal gear rotor. As the drive gear rotates and pulls the driven gear around, the volume of the cavity increases until it reaches its maximum. During the rotation, the expanding cavity is under the inlet port and fluid is drawn into the pump. As the gears continue to rotate, the cavity formed by the marked teeth moves under the outlet port. As the drive gear meshes with the cavity next to the marked cavity in the rotor, its volume decreases. The fluid in this cavity is forced out of the pump through the outlet port. Gerotor type pump 2022-08-08 B1-15b Gas Turbine Engine Page 58 of 291 CASA Part 66 - Training Materials Only  Gerotor type pump (animated) 2022-08-08 B1-15b Gas Turbine Engine Page 59 of 291 CASA Part 66 - Training Materials Only  Scavenge Pumps In addition to a pressure pump, almost all turbine engine lubrication systems must utilise a scavenge pump to return oil to the oil reservoir. A scavenge pump may be a gear, vane or gerotor type pump that is driven by the engine. As a rule, scavenge pumps have a capacity that is greater than a pressure pump. The reason for this is that after oil flows through an engine, it typically has a greater volume due to foaming and thermal expansion. Therefore, to ensure that oil does not collect in the engine sump, the scavenge pump must be capable of pumping a greater volume of oil than the pressure pump. One unique feature of many turbine engine oil pumps is that the pressure pump and scavenge pump are often enclosed in a single housing. © Aviation Australia Scavenge type pump cutaway 2022-08-08 B1-15b Gas Turbine Engine Page 60 of 291 CASA Part 66 - Training Materials Only  Valves Valve Types The four most common types of valves used in gas turbine engine oil systems are: Pressure relief valves Check valves Thermostatic bypass valves Pressure bypass valves. Pressure Relief Valves Pressure relief valves are used to limit and adjust the maximum pressure within the oil system. The spring-loaded relief valve is designed to open and bypass oil back to the inlet side of the pump whenever the oil pressure exceeds the pressure of the spring on the valve. Oil pressure can be adjusted by adjusting the pressure of the spring on the valve. Aviation Australia Pressure relief valve 2022-08-08 B1-15b Gas Turbine Engine Page 61 of 291 CASA Part 66 - Training Materials Only  Check Valves Check valves are installed in the oil supply line downstream of the pressure pump. Their purpose is to prevent oil seeping through the pressure pump and into the engine when the engine is stationary. The check valve may be a simple ball-and-spring design. As the oil pressure drops to zero (i.e. the engine stops), the spring forces the ball against its seat to stop the oil gravity feeding into the engine. When the engine starts and the oil pressure rises to a predetermined pressure, the valve is unseated and oil flows through the system. Another type utilises a cone and spring. Aviation Australia Check valves 2022-08-08 B1-15b Gas Turbine Engine Page 62 of 291 CASA Part 66 - Training Materials Only  Thermostatic Bypass Valves Thermostatic bypass valves are fitted to oil cooler outlets to maintain the correct oil temperature. They also quickly bypass oil to the lubrication points on a cold start. When the oil is cold, the valve is open, allowing the oil to bypass the cooler as shown in the illustration. As the oil heats up, the valve closes and directs more oil through the cooler matrix as shown. Aviation Australia Thermostatic bypass valve 2022-08-08 B1-15b Gas Turbine Engine Page 63 of 291 CASA Part 66 - Training Materials Only  Bypass Valves Bypass valves are fitted to the oil system to prevent the engine being starved of oil in the event of a blocked component, e.g. a filter. They operate on the same principle as pressure relief valves. When the blockage occurs, the system senses an increase in pressure, the bypass valve is forced off its seat and oil is allowed to bypass the blocked component. Bypass valves are fitted to all filters and oil coolers. A pop-up indicator on the filter or a cockpit light may signal a blocked component. Within the oil cooler, the bypass and thermostatic valves are usually incorporated as one unit. Aviation Australia Bypass valves 2022-08-08 B1-15b Gas Turbine Engine Page 64 of 291 CASA Part 66 - Training Materials Only  Oil Filters Filters in Oil Systems Once oil is discharged from an oil pressure pump, it flows to an oil filter. The purpose of the oil filter is to remove contaminants from the lubrication system. The common types of filters in oil systems are: Laminated paper Cleanable screen Screen and spacer Thread filters. Aviation Australia Lubrication system showing main oil filter and scavenge filters 2022-08-08 B1-15b Gas Turbine Engine Page 65 of 291 CASA Part 66 - Training Materials Only  Laminated Paper Laminated paper filters consist of a pleated paper element assembled around a steel core. The element is pleated to considerably increase the surface area of the filter element. Oil flows from the outside through the element, which traps the contaminants, and then out through the centre to the outlet port. Aviation Australia Laminated paper filter 2022-08-08 B1-15b Gas Turbine Engine Page 66 of 291 CASA Part 66 - Training Materials Only  Cleanable Screen Cleanable screen filters may be cylindrical or pleated, depending on the system in which they are used. Screen filters are used in both pressure and scavenge systems, and their degree of filtration depends on the micron size of the elements used, that is, the lower the micron size, the finer the degree of filtration. They range from coarse strainers to fine pressure filters. They operate on the same principle as the laminated paper filters, but are cleaned and reused rather than disposed of. Aviation Australia Cleanable screen filter 2022-08-08 B1-15b Gas Turbine Engine Page 67 of 291 CASA Part 66 - Training Materials Only  Screen and Spacer Screen and spacer filters work on the same principle as both screen and paper filters. In the screen and spacer filter, shown below, the elements are disc-shaped and stack onto the element support. Oil flows in through both sides of the filter discs separated by the spacer, into the perforated tube and out to the system. These filters are normally used as pressure filters and are fitted downstream of the pump. Screen and spacer filter 2022-08-08 B1-15b Gas Turbine Engine Page 68 of 291 CASA Part 66 - Training Materials Only  Thread Filters Thread filters are used as ‘last chance’ filters. They are placed just before the jets that spray oil into a bearing to prevent blockage of the jet. This is the last chance to filter the oil before it enters the bearings, thus the name. They consist of an inner threaded element which is enclosed by an unthreaded outer casing. Oil passes through the outer casing, across the threads being filtered, into the centre of the inner element and then on to the oil jet. The filtration required is achieved by selecting a coarser- or finer- pitched thread on the threaded portion of the filter. The finer the pitch, the greater the degree of filtration. Threaded filter 2022-08-08 B1-15b Gas Turbine Engine Page 69 of 291 CASA Part 66 - Training Materials Only  Oil Filter Bypass It is a regulatory requirement that all oil filters be constructed and installed in a way that permits full oil flow even if the filter becomes completely blocked. Therefore, some means of bypassing the filter must be provided. The most common way to meet this requirement is to incorporate an oil bypass valve that automatically lets oil bypass the filter entirely once it becomes plugged. Since the use of unfiltered oil to lubricate main bearings can cause extensive damage, most turbine-powered aircraft have a warning light in the cockpit to notify the operator when the filter is being bypassed. Often a red ‘pop- out’ clogging indicator is added to the filter housing as a visual bypass warning. Oil filter bypass Oil Filter Bypass Warning and Indication Oil filter impending bypass warning instrumentation is also installed in many engines to tell flight and maintenance personnel that the main oil filter is approaching a blocked condition or is completely blocked. It is adjusted to actuate at a differential pressure sufficiently less than what the filter will start bypassing to permit flight crews to take timely action and prevent bypassing of unfiltered oil. Such instrumentation is considered a maintenance aid because timely action in most cases prolongs the life of the engine components. 2022-08-08 B1-15b Gas Turbine Engine Page 70 of 291 CASA Part 66 - Training Materials Only  Oil System Components Oil Coolers The purpose of all oil coolers is to maintain a specific oil temperature under differing oil heat conditions which occur at various engine speeds. Oil coolers are of two basic types: fuel-cooled air-cooled. The oil cooler in a turbine engine may be located in either the pressure subsystem or the scavenge subsystem. When installed in the pressure subsystem, the lubrication system is sometimes referred to as a hot tank system because the scavenge oil is not cooled before it enters the reservoir. On the other hand, when the oil cooler is placed in the scavenge subsystem, the lubrication system is often referred to as a cold tank system because the oil is cooled just before it enters the reservoir. Oil cooler 2022-08-08 B1-15b Gas Turbine Engine Page 71 of 291 CASA Part 66 - Training Materials Only  Fuel-Cooled Oil Coolers The fuel-cooled oil cooler is the most common engine oil cooler on larger engines, but is also used on many smaller engines. It consists of a large number of tubes (not unlike drinking straws), called a matrix, contained within a sealed outer case. The tubes convey the fuel through the cooler while oil is circulated around the outside of the tubes by baffle plates. Heat is transferred from the oil to the fuel. This heating of the fuel is desirable to prevent fuel system component icing. Many fuel-cooled oil coolers contain a combination differential pressure bypass valve and thermostatic bypass valve at the cooler inlet. When the oil is cold, the valve is open and the oil is allowed to bypass the cooler and flow directly into the oil system. As the oil heats up, the thermostatic bypass valve expands and closes the bypass passage, which forces the oil to travel through the cooler. If the cooler becomes blocked, the pressure of the oil increases until it forces the differential pressure bypass valve off its seat. This causes the oil to bypass the cooler and be available for use, uncooled, by the engine. This condition is shown in the top diagram below, which illustrates the oil flow when the bypass valve is open. The bottom diagram illustrates the oil flow when the bypass valve is closed. Fuel-cooled oil cooler, "Bypass valve open" 2022-08-08 B1-15b Gas Turbine Engine Page 72 of 291 CASA Part 66 - Training Materials Only  Fuel-cooled oil cooler, "Bypass valve closed" 2022-08-08 B1-15b Gas Turbine Engine Page 73 of 291 CASA Part 66 - Training Materials Only  Air-Cooled Oil Coolers Air-cooled oil coolers use the same principles of operation as the fuel-cooled oil cooler. Its oil is cooled by air that flows through the matrix. The air-cooled oil cooler also uses the same bypass and thermostatic valve systems as the fuel-cooled oil cooler. Air is directed through the cooler by a thermostatically controlled air scoop, which regulates the temperature of the oil by controlling the quantity of air that is allowed to pass through the cooler. Air cooled oil cooler 2022-08-08 B1-15b Gas Turbine Engine Page 74 of 291 CASA Part 66 - Training Materials Only  Oil Jets After the oil passes through the pressure pump and filter, it must be distributed to the points which require lubrication. The oil jets serve this purpose. The pressure oil is forced through the calibrated orifice and delivered in the form of an oil spray or a fluid stream onto bearings, oil seals, gears and other parts. The fluid stream is by far the most commonly used system, especially where high pressure loads are involved. In most cases, this stream of oil is directed onto the bearing surface by what is sometimes called a direct-lubrication oil jet. Some engines use compressor bleed air to deliver an air/oil mist spray through a mist- and vapour-lubrication oil jet. This allows for a wider area of lubrication from a single oil jet and is utilised in some of the larger engines. A newer type of oil jet is coming into use called an under-race lubrication jet. This system routes oil down the rotor shafts and bearing journals, then feeds it through slots acting as oil jets in the bearing inner races. It is claimed that this system achieves superior cooling compared to conventional spray jet lubrication. Aviation Australia Oil Jets 2022-08-08 B1-15b Gas Turbine Engine Page 75 of 291 CASA Part 66 - Training Materials Only  © Aviation Australia Under race lubrication Vents Vents, or breathers, are fitted to oil tanks and bearing chambers to prevent an undesirable build-up of excess air pressure. This pressure results from sealing air leaking across carbon and labyrinth type oil seals. The diagram below shows this application to a labyrinth type oil seal. Some air pressure is required within the tank to assist gravity feeding of the oil, and in the bearing chambers, to allow proper scavenge and oil jet spray. The most common type of vent system is the centrifugal breather. As the oil-laden air enters the rotating slinger chamber of the breather, centrifugal force flings the oil outwards to drain back into the sump while the clean vent air is routed overboard, or to a pressurising and vent valve in the reservoir and then overboard. Aviation Australia Oil Vent 2022-08-08 B1-15b Gas Turbine Engine Page 76 of 291 CASA Part 66 - Training Materials Only  Oil vent system Most vent systems use a vent pressurising valve to maintain 5–7 psi head of pressure within the tank and bearing chambers. The vent-pressurising valve consists of an aneroid bellows with sea-level air pressure trapped inside, and a spring-loaded pressure relief valve in the overboard vent line. At sea level the vent is open, but it closes as the altitude increases in order to maintain the vent pressure the same as it is at sea level. The aneroid capsule typically begins to close at an altitude of about 8000 ft and completely closes at about 20 000 ft. The vent system then acts as a pressurising check valve and maintains the pressure at 5–7 psi. 2022-08-08 B1-15b Gas Turbine Engine Page 77 of 291 CASA Part 66 - Training Materials Only  Oil system vent valve 2022-08-08 B1-15b Gas Turbine Engine Page 78 of 291 CASA Part 66 - Training Materials Only  Chip Detectors and Magnetic Plugs Many scavenge subsystems contain permanent magnet chip detectors (MCDs) that attract and hold ferrous metal particles. These chip detectors are used for several reasons: First, any metal particles that are attracted to the detector are prevented from circulating in the engine and causing additional wear. Second, the collection of metal particles on an MCD provides valuable information when troubleshooting engine problems. As a general rule, the presence of small fuzzy particles or grey metallic paste is the result of normal engine wear and is therefore not a cause for concern. However, metallic chips or flakes indicate serious internal wear which must be investigated further. Normally one MCD is located in each of the following locations: Engine forward-bearing sump Engine rear-bearing sump Accessory gearbox Transfer gearbox. Their location is normally labelled to identify the scavenge system they belong to. When removed, the MCD closes off a valve to prevent oil leakage. Chip detector A quick-disconnect bayonet fitting attachment is common. 2022-08-08 B1-15b Gas Turbine Engine Page 79 of 291 CASA Part 66 - Training Materials Only  Some chip detectors incorporate an electric circuit that operates an indicator light in the cockpit. With this type of MCD, sometimes called an indicating chip detector, a positive electrode is placed in the centre of the detector while a negative or ground electrode is placed on the detector shell. In this configuration, when metallic debris bridges the gap between the positive and ground electrodes, the indicator circuit is completed and the warning light illuminates. The flight crew must then respond to the warning and take the necessary precautions to prevent engine damage and ensure flight safety. Quick disconnect bayonet fitting Aviation Australia Chip detector warning circuit 2022-08-08 B1-15b Gas Turbine Engine Page 80 of 291 CASA Part 66 - Training Materials Only  Lubrication System Types Pressure Relief Valve System A typical pressure relief lubrication system consists of an oil reservoir, pressure and scavenge pumps, a pressure relief valve (pressure regulating valve), several oil filters, oil jets, an oil cooler and vent lines. In a turbine engine, the pressure within the bearing chambers increases dramatically with increases in engine speed. As the pressure within the bearing chambers increases, the pressure differential between the bearing chambers and the lubrication system decreases. The lower the pressure differential, the less oil flows to the bearings. To prevent this from happening, some of the pressurised air within the bearing chambers is typically routed to the back side of the pressure relief valve to augment the spring pressure. This way, as the engine speed increases, the pressure within the lubrication system also increases. Pressure relief valve engine lubricating system 2022-08-08 B1-15b Gas Turbine Engine Page 81 of 291 CASA Part 66 - Training Materials Only  Full Flow Systems In a full-flow system, no pressure relief valve is used; therefore, the amount of oil that flows to the bearings is directly related to how fast the engine and oil pump are run. In this case, the size of the oil pump is determined by the oil flow required at the engine’s maximum operating speed. Full flow engine lubricating system 2022-08-08 B1-15b Gas Turbine Engine Page 82 of 291 CASA Part 66 - Training Materials Only  Oil System Indication Oil System Indicators Gauge connection provisions are incorporated in the oil system for oil pressure, oil quantity, low oil pressure, oil filter differential pressure switch and oil temperature. A turbine engine pressure gauge is typically connected to the oil system downstream of the main oil filter. This location ensures an indication of the actual pressure being delivered to the engine. As an additional feature, some oil pressure systems incorporate a low-pressure warning light. When aircraft electrical power is turned on and the engine is not running, each engine’s low oil pressure light illuminates. However, when the engine is starting, the warning light should extinguish once oil pressure increases above the low limit marked on the oil pressure gauge. The oil temperature sensor is located in the pressure line before the oil goes to the engine bearings and after it passes through all other oil system components (filter, coolers, relief valves) Engine oil system indication 2022-08-08 B1-15b Gas Turbine Engine Page 83 of 291 CASA Part 66 - Training Materials Only  ECAM / EICAS Engine Oil Indication In today’s aircraft, the engine oil indication and warning system is displayed electronically in the cockpit on the ECAM or EICAS displays. Oil system information on a digital display (EICAS/ECAM) Relevant Youtube link: Lubrication System 1 (Video) Relevant Youtube link: Lubrication System 2 (Video) 2022-08-08 B1-15b Gas Turbine Engine Page 84 of 291 CASA Part 66 - Training Materials Only