What is the primary purpose of the oil system in a reciprocating aircraft engine?
ACS code: AM.III.G
Correct answer: To reduce friction between moving parts by lubricating bearing surfaces
Rationale: The handbook lists several functions of engine oil, but the principal one is lubrication—forming an oil film between moving parts to reduce friction and wear. Oil also cools, cleans, seals, and cushions, but lubrication is the primary purpose. Oil does not raise combustion temperature and is not the source of landing-gear hydraulic power.
Besides lubrication, which additional function does engine oil perform in a reciprocating engine?
ACS code: AM.III.G
Correct answer: It carries heat away from internal engine parts
Rationale: In addition to reducing friction, oil cools the engine by absorbing heat from pistons, bearings, and other internal parts and transferring it to the oil cooler. Oil also seals, cleans, and cushions, but it has no role in fuel delivery to the carburetor or in producing ignition spark.
In a dry-sump oil system, where is the main supply of engine oil stored?
ACS code: AM.III.G
Correct answer: In a separate external oil tank
Rationale: A dry-sump system stores the bulk of its oil in a separate tank mounted away from the engine, and a scavenge pump returns oil from the engine sump to that tank. A wet-sump system, by contrast, keeps the oil supply in the crankcase sump. The oil cooler is a heat exchanger, not a storage reservoir.
Which type of pump is most commonly used as the engine-driven oil pump in a reciprocating engine?
ACS code: AM.III.G
Correct answer: A gear-type positive-displacement pump
Rationale: The handbook identifies the gear-type pump as the most widely used oil pump in reciprocating engines. It is a positive-displacement pump in which two meshing gears carry oil around the housing and force it out under pressure. Centrifugal pumps lack positive displacement, and diaphragm pumps are typically used for fuel, not engine oil.
What is the function of the oil pressure relief valve in a lubrication system?
ACS code: AM.III.G
Correct answer: It limits oil pressure to a safe maximum value
Rationale: The oil pressure relief valve regulates system pressure by opening to bypass excess oil back to the inlet or sump once pressure reaches a set value, protecting the system from excessive pressure. It does not boost pressure on cold starts, and metal-particle removal is the job of the oil filter, not the relief valve.
What is the purpose of an oil cooler bypass (thermostatic) valve?
ACS code: AM.III.G
Correct answer: It routes oil around the cooler until the oil reaches operating temperature
Rationale: The thermostatic bypass valve senses oil temperature and directs cold oil around the cooler core, sending oil through the cooler only after it warms up. This helps the oil reach operating temperature quickly and keeps it within the proper range. It does not divert cold oil into the cooler, nor does it gate flow to the bearings.
In a dry-sump engine, why is the scavenge pump usually built with greater capacity than the pressure pump?
ACS code: AM.III.G
Correct answer: Because the returning oil is aerated and occupies more volume
Rationale: Scavenged oil returning from the engine is mixed with air and foams, so it occupies a greater volume than the solid oil delivered by the pressure pump. To keep the sump clear and prevent the oil from backing up, the scavenge pump is given greater capacity. Tank position and oil viscosity are not the reasons for the larger scavenge capacity.
What does an oil temperature that is too high during normal cruise most commonly indicate?
ACS code: AM.III.G
Correct answer: Insufficient oil supply or a restriction in the oil cooler
Rationale: Excessively high oil temperature commonly results from a low oil quantity or a restriction in the cooler that prevents adequate heat removal, both of which reduce the oil's ability to carry heat away. An overfilled tank or low-viscosity oil are not the typical causes; the handbook ties high oil temperature chiefly to inadequate cooling or low supply.
What is the function of the oil filter in a reciprocating engine lubrication system?
ACS code: AM.III.G
Correct answer: To remove foreign particles and contaminants from the circulating oil
Rationale: The oil filter traps dirt, carbon, metal particles, and other contaminants so that clean oil reaches the bearings and other moving parts, helping prevent wear and damage. Heating the oil is not its purpose, and regulating delivered oil volume is handled by the pump and relief valve, not the filter.
A turbine engine bearing oil seal failure would most likely cause
ACS code: AM.III.G
Correct answer: high oil consumption.
Rationale: The bearing oil seal keeps lubricating oil within the bearing chamber. If it fails, oil escapes from the chamber, often past the seal into the gas path where it is burned, so the most likely symptom is high oil consumption rather than a pressure or temperature change (FAA-H-8083-32, Turbine Engine Lubrication).
Why are the labyrinth oil seals around a turbine engine bearing chamber pressurized with air?
ACS code: AM.III.G
Correct answer: To ensure minimum loss of oil from the bearing chamber.
Rationale: Bearing chambers are sealed with air-pressurized (labyrinth) seals so that sealing air flows inward across the seal, opposing the escape of oil. Maintaining this air pressure differential keeps oil inside the chamber and reduces oil loss into the gas path. It is not used to force oil into the bearings (FAA-H-8083-32, Bearings and Seals).
In a turbine engine, the oil seals on the rotating assembly are kept oil-tight primarily by means of
ACS code: AM.III.G
Correct answer: pressurized sealing air directed across the seal.
Rationale: The oil seals on the rotating assembly are air-type seals: a supply of sealing air at a pressure higher than the bearing chamber flows across the seal toward the oil, opposing oil escape. This pressurized air keeps the seal oil-tight, unlike garter springs or expander rings used in static seals.
A high viscosity index in a lubricating oil indicates that the oil's viscosity
ACS code: AM.III.G
Correct answer: will not vary greatly with changes in temperature.
Rationale: Viscosity index measures how much an oil's viscosity changes with temperature. A high viscosity index means the viscosity stays comparatively stable, so it does not vary greatly with temperature change, keeping the oil neither too thick when cold nor too thin when hot.
What is a fuel-system icing inhibitor designed to prevent from freezing in turbine fuel?
ACS code: AM.III.G
Correct answer: The water entrained or dissolved in the fuel.
Rationale: A fuel-system icing inhibitor acts on the small amount of water dissolved or entrained in the fuel, lowering its freezing point so it cannot form ice crystals that block filters at low temperatures. It does not stop the kerosene-type fuel itself from freezing; it targets the water in the fuel.
What is the most likely result of operating an engine at extremely high temperatures using a lubricant the manufacturer recommends for a much lower temperature?
ACS code: AM.III.G
Correct answer: The oil pressure will be lower than normal.
Rationale: An oil intended for a lower temperature becomes too thin when run at a much higher temperature, so its viscosity drops. The thinner oil flows and leaks past clearances more easily, producing oil pressure lower than normal and risking inadequate film strength.
The lubricating oil used in a gas turbine engine is usually a
ACS code: AM.III.G
Correct answer: synthetic oil rated for high-temperature turbine service.
Rationale: Gas turbine engines normally use synthetic oils because they remain stable at the very high bearing temperatures and resist oxidation and coking far better than mineral oils. Mineral oils break down at turbine operating temperatures and are unsuitable.
In spectrometric oil analysis (SOAP), the oil spectrometer measures the
ACS code: AM.III.G
Correct answer: concentration of metallic wear particles suspended in the oil.
Rationale: An oil spectrometer used in spectrometric oil analysis measures the concentration of metallic contaminants suspended and dissolved throughout the oil sample, identifying which engine components are wearing. It analyzes fine particulate and dissolved metals, not just surface debris or specific gravity.
In a fuel/oil cooler (heat exchanger), the oil pressure is normally maintained
ACS code: AM.III.G
Correct answer: higher than the fuel pressure.
Rationale: In a fuel/oil cooler the oil is kept at a higher pressure than the fuel so that any internal leak passes oil into the fuel rather than fuel into the oil system. This protects the engine bearings from fuel contamination and oil dilution.
When operating, a gear-type (external gear) oil pump moves oil by
ACS code: AM.III.G
Correct answer: carrying it in the spaces between the gear teeth and the pump casing.
Rationale: A gear-type external gear pump draws oil in at the inlet and traps it in the spaces between the gear teeth and the casing, carrying it around to the outlet. The meshing teeth form a seal so oil cannot pass back through the center, giving positive-displacement delivery.
A scavenge filter is incorporated in a gas turbine lubrication system to
ACS code: AM.III.G
Correct answer: protect the pressure pump from debris carried in the returning oil.
Rationale: Scavenge oil returning from the bearing chambers carries any debris before it passes back to the tank and then to the pressure pump. The scavenge filter removes this debris so that the pressure pump and the downstream bearing feed jets are protected from contamination.
On a turbine engine showing no change in power-setting parameters but a high oil temperature, a likely cause is
ACS code: AM.III.G
Correct answer: distress of an engine main bearing.
Rationale: If the power-setting parameters are unchanged but oil temperature is high, the extra heat is being generated by friction at a rotating part rather than in the gas path. A distressed main bearing produces this localized heating, raising oil temperature without affecting the thrust indications.
In most turbine engines, the lubricating oil is cooled by
ACS code: AM.III.G
Correct answer: a fuel/oil cooler (heat exchanger).
Rationale: Turbine engine oil is usually cooled in a fuel/oil heat exchanger, where heat passes from the hot oil into the cooler fuel on its way to the burners. This simultaneously cools the oil and warms the fuel, helping prevent fuel system icing.
What type of filter is used to protect the oil pressure spray jets in a turbine engine lubrication system?
ACS code: AM.III.G
Correct answer: In-line thread-type (last-chance) filters.
Rationale: Oil pressure spray jets are protected by small in-line, thread-type last-chance filters fitted immediately ahead of each jet. These catch any debris that would otherwise block the fine spray orifice and are positioned in the line feeding the individual jets.
A chip detector in a turbine engine oil system is a
ACS code: AM.III.G
Correct answer: magnetic plug installed in the scavenge (return) line.
Rationale: A chip detector is a magnetic plug fitted in the scavenge (return) line, where it attracts and collects ferrous wear particles from the returning oil. Inspecting the captured debris helps reveal impending bearing or gear failure.
When operating, a gerotor-type oil pump moves oil by
ACS code: AM.III.G
Correct answer: carrying it through the changing volumes formed by the intermeshing rotors to the outlet.
Rationale: In a gerotor-type pump an inner rotor meshes with an outer rotor, and as they turn the oil is drawn in, carried through the changing volumes formed by the intermeshing lobes, and delivered to the outlet. The action carries the oil through the meshing elements rather than only around the outside of the casing.
Engine oil picks up the most heat from which of the following turbine engine components?
ACS code: AM.III.G
Correct answer: The turbine bearing.
Rationale: The turbine bearing sits closest to the hottest section of the engine, so the oil lubricating and cooling it absorbs the most heat. Compressor bearings and rotor couplings run in cooler regions and transfer far less heat to the oil.
In a turbine engine that uses a fuel-oil heat exchanger, the oil temperature is controlled by a thermostatic valve that regulates the flow of
ACS code: AM.III.G
Correct answer: oil through the heat exchanger.
Rationale: In a fuel-oil heat exchanger, a thermostatic valve controls how much oil passes through the cooler core versus bypassing it. Per FAA-H-8083-32, the fuel flows continuously on its way to the nozzles, so the oil side is modulated to hold the desired oil temperature.
What is the purpose of the last-chance oil filters in a turbine engine lubrication system?
ACS code: AM.III.G
Correct answer: To prevent clogging of the oil spray nozzles.
Rationale: Per FAA-H-8083-32, a last-chance filter is a final fine screen fitted just upstream of each oil spray nozzle. It catches any particles that escaped earlier filters so the small spray orifice cannot become blocked, preventing loss of bearing lubrication.
Which of the following is a function of the fuel-oil heat exchanger on a turbojet engine?
ACS code: AM.III.G
Correct answer: Increases fuel temperature.
Rationale: Per FAA-H-8083-32, the fuel-oil heat exchanger transfers heat from the hot engine oil into the fuel, raising fuel temperature while cooling the oil. Warming the fuel also helps prevent ice from forming in the fuel system. It neither aerates the fuel nor emulsifies the oil.
At cruise RPM, some oil will flow through the relief valve of a gear-type engine oil pump. This is normal because the relief valve is set at a pressure that is
ACS code: AM.III.G
Correct answer: lower than the pressure pump capabilities.
Rationale: Per FAA-H-8083-32, the relief valve is set below the maximum pressure the pump can produce, so at cruise RPM the pump exceeds that setting and a small amount of oil is continuously relieved. This regulates system pressure and prevents over-pressurization.
After making a welded repair to a pressurized-type turbine engine oil tank, the tank should be pressure-checked to
ACS code: AM.III.G
Correct answer: not less than 5 PSI plus the maximum operating pressure of the tank.
Rationale: Per FAA-H-8083-32, after a welded repair a pressurized oil tank must be proof-tested to verify the repair is leak-free and strong. The standard test value is not less than 5 PSI above the tank's maximum operating pressure, ensuring integrity at worst-case in-service conditions.
Failure-related ferrous metal particles in turbine engine oil cause an electrical-indicating type magnetic chip detector to indicate their presence by
ACS code: AM.III.G
Correct answer: bridging the gap between the detector center (positive) electrode and the ground electrode.
Rationale: Per FAA-H-8083-32, an electrical-indicating chip detector has a center electrode and a surrounding ground electrode separated by a small gap. Conductive ferrous particles attracted by the magnet bridge this gap, completing the circuit and triggering the cockpit warning.
What would be the probable result if the oil system pressure relief valve should stick in the open position on a turbine engine?
ACS code: AM.III.G
Correct answer: Insufficient lubrication.
Rationale: Per FAA-H-8083-32, if the pressure relief valve sticks open, oil is continuously diverted back to the inlet side and system oil pressure falls. The reduced pressure cannot deliver adequate oil to the bearings, resulting in insufficient lubrication and possible bearing damage.
What is the primary purpose of the oil-to-fuel heat exchanger on a turbine engine?
ACS code: AM.III.G
Correct answer: Cool the oil.
Rationale: Per FAA-H-8083-32, the primary purpose of the oil-to-fuel heat exchanger is to cool the engine oil by transferring its heat into the comparatively cool fuel. Warming the fuel is a useful secondary effect that helps prevent fuel icing, but oil cooling is the main function.
What type of oil system is usually found on turbine engines?
ACS code: AM.III.G
Correct answer: Dry sump, pressure, and spray.
Rationale: Per FAA-H-8083-32, turbine engines typically use a dry-sump system in which oil is stored in a separate tank, combined with a pressure feed to the bearings and oil delivered as a spray through fine jets. Dip and splash methods cannot reliably lubricate the high-speed bearings of a gas turbine.
The type of oil pumps most commonly used on turbine engines are classified as
ACS code: AM.III.G
Correct answer: positive displacement.
Rationale: Per FAA-H-8083-32, turbine engine oil pumps are positive-displacement types, such as gear or gerotor pumps, which deliver a fixed volume of oil per revolution regardless of outlet pressure. This guarantees a steady oil supply proportional to engine speed.
What will result if an engine oil filter becomes completely blocked?
ACS code: AM.III.G
Correct answer: Oil will flow at the normal rate through the system.
Rationale: Per FAA-H-8083-32, a blocked oil filter causes the bypass (relief) valve to open, allowing oil to flow around the filter and continue to the engine at the normal rate. The oil is then unfiltered, but lubrication is maintained to prevent bearing failure.
A turbine engine dry-sump lubrication system of the self-contained, high-pressure design
ACS code: AM.III.G
Correct answer: consists of pressure, breather, and scavenge subsystems.
Rationale: Per FAA-H-8083-32, a self-contained high-pressure dry-sump system comprises three subsystems: pressure, which feeds oil to the bearings; scavenge, which returns it from the bearing chambers; and breather, which controls chamber pressure. Oil is held in a separate tank, not in a crankcase.
What is the primary purpose of the hopper located in the oil supply tank of some dry-sump engine installations?
ACS code: AM.III.G
Correct answer: To reduce the time required to warm the oil to operating temperature.
Rationale: Per FAA-H-8083-32, the hopper isolates a smaller volume of oil within the tank so only that quantity must be warmed initially. This reduces the time taken for the oil to reach operating temperature after a cold start, improving warm-up performance.
What determines the minimum particle size that will be excluded by a Cuno-type (stacked-disc, edge-filtration) oil filter?
ACS code: AM.III.G
Correct answer: The spacer thickness.
Rationale: Per FAA-H-8083-32, in a Cuno stacked-disc edge-filtration filter the cleaning blades pass through gaps set by spacers between the discs. The thickness of those spacers fixes the clearance and therefore the minimum particle size that can pass, so spacer thickness determines the filtration fineness.
A full-flow oil system has
ACS code: AM.III.G
Correct answer: a variable oil pressure dependent upon throttle setting.
Rationale: Per FAA-H-8083-32, in a full-flow system the positive-displacement pump delivers oil at a rate set by engine speed, so the oil pressure rises and falls with throttle (RPM) setting rather than being held at a single fixed value or switched between hot and cold limits.
A felt-type oil filter element in a turbine engine lubrication system should be
ACS code: AM.III.G
Correct answer: removed and replaced with a new filter element.
Rationale: A felt filter element traps contaminants within its fibrous body and cannot be satisfactorily cleaned, because solvents leave a residue and degrade the felt. Per FAA-H-8083-32, this type of element is a throwaway item and must be removed and replaced with a new element at the specified interval.
What type of filter is generally fitted on the inlet side of a turbine engine oil scavenge pump?
ACS code: AM.III.G
Correct answer: A wire-mesh screen filter.
Rationale: A coarse wire-mesh (screen) filter is fitted on the inlet side of a scavenge pump to catch larger debris before the oil enters the pump, protecting it without unduly restricting the high flow of aerated scavenge oil. FAA-H-8083-32 describes these inlet screens in the scavenge subsystem.
The output of a vane-type oil pump is controlled by
ACS code: AM.III.G
Correct answer: outlet pressure acting against spring pressure.
Rationale: A vane-type oil pump regulates its delivery by balancing outlet (delivery) pressure against a control spring, which adjusts the eccentricity or relief path so that delivery pressure is held within limits as engine speed varies. FAA-H-8083-32 describes pressure-regulated positive-displacement oil pumps.
In a dry-sump turbine engine oil system, the sump
ACS code: AM.III.G
Correct answer: is used as a collecting point only.
Rationale: In a dry-sump system the sump serves only as a collecting point for oil draining from the bearing chambers, from where the scavenge pumps return it to a separate oil tank. Per FAA-H-8083-32, the bulk of the oil is stored in the external tank, not in the sump.
A turbine engine gearbox breather is prevented from losing oil to the atmosphere by the action of
ACS code: AM.III.G
Correct answer: an impeller and centrifugal force.
Rationale: A centrifugal breather uses a rotating impeller to fling oil droplets outward by centrifugal force, separating them from the breather air. Per FAA-H-8083-32, the de-oiled air is vented to atmosphere while the separated oil is returned to the system, preventing oil loss through the breather.
An air-cooled oil cooler is fitted with an anti-surge (bypass) valve in order to
ACS code: AM.III.G
Correct answer: protect the cooler core from over-pressure damage.
Rationale: The anti-surge valve opens to bypass oil around the cooler core when a pressure surge occurs, such as with cold, thick oil at start-up. Per FAA-H-8083-32, this protects the cooler core from over-pressure damage; it does not set general engine oil pressure.
A thread-type (screw-type) oil seal in a lubrication system
ACS code: AM.III.G
Correct answer: has a thread on a stationary portion that pumps oil back toward the bearing.
Rationale: A thread (screw) type oil seal has a fine thread cut into a stationary member surrounding the rotating shaft. As the shaft turns, the thread pumps any escaping oil back toward the bearing, preventing leakage along the shaft. FAA-H-8083-32 describes such dynamic shaft seals.
The oil system generally used on most modern turboprop engines is the
ACS code: AM.III.G
Correct answer: dry-sump type.
Rationale: Most modern turboprop engines use a dry-sump oil system, storing oil in a separate tank with engine-driven pressure and scavenge pumps. Per FAA-H-8083-32, this suits their high-speed bearings and varying attitudes far better than a wet-sump arrangement.
Compared with other positive-displacement designs, a spur-gear oil pump generally produces
ACS code: AM.III.G
Correct answer: a low flow rate at high pressure.
Rationale: A spur-gear pump is a positive-displacement pump that moves a relatively small, fixed volume per revolution but can develop high delivery pressure. Per FAA-H-8083-32, this makes it well suited as the engine pressure-supply pump in a lubrication system.