8083 Powerplant Orals

1-1(O). What is the reciprocating engine theory of operation?

1-1(O). A reciprocating engine is an internal combustion device that converts the energy in fuel into mechanical energy. A compressed fuel/air charge is burned in each cylinder of the engine. The energy released pushes the piston down in successive cylinders so that the crankshaft, which is attached to the pistons via connecting rods, develops a rotational motion (force). This force is transferred to a propeller geared off of the end of the crankshaft to produce thrust. A camshaft is geared to the crankshaft to enable valves to open and close at precise times. The valves let the fuel/air mixture into each cylinder and, after the charge is burned, the valves let the exhaust gases out. Magnetos develop a high-tension current that is distributed to successive cylinders at the precise time it is advantageous to ignite the fuel air mixture. Most reciprocating aircraft engines are 4- stroke cycle engines. A stroke is the movement of the piston in the cylinder from top to bottom or from bottom to top. The 4 strokes are labeled to indicate their function in the cycle. They are in order of occurrence: the intake, compression, power, and exhaust strokes. Ignition of the fuel/air mixture via spark plugs in each cylinder occurs just before the piston reaches the top of the compression stroke. The force created by burning the fuel is then transmitted by the piston to the crankshaft on the power stroke.

1-10(O). What is the purpose of a turbine engine diffuser?

1-10(O). The diffuser is the divergent section of the engine after the compressor and before the combustion section. It functions to reduce the velocity of the compressor discharge air and increase its pressure so that it can be combined with fuel and burned in the combustion section. The lower velocity of the gases aids in the continuous burning process. If the gases pass through the combustion section at too high of a velocity, the flame could extinguish.

1-11(O). What type of engine is a typical APU (auxiliary power unit)? What is its function and how does it operate?

1-11(O). A typical APU is a turboshaft gas turbine engine that is made to transfer horsepower to a shaft. The shaft turns the engine compressor from which bleed air for the aircraft is obtained. It also drives an accessory gearbox that rotates a generator. The generator supplies the aircraft with electrical power on the ground and in the air. The APU is often operated with no personnel on the flight deck.

1-2(O). What is the basic radial engine design and how does it operate?

1-2(O). Radial engines are simply reciprocating engines with the cylinders arranged radially around a central crankcase and crankshaft. It operates like any other 4-stroke cycle reciprocating engine.

1-3(O). What is firing order and how is it determined?

1-3(O). The firing order of an engine is the sequence in which the power event occurs in the different cylinders. Firing order is designed to provide for balance and to eliminate vibration. It is set by the engineers of the engine. Cylinder firing order in opposed reciprocating aircraft engines is usually listed in pairs of cylinders as each pair fires across the center main bearing. On single row radial engines, the firing order is the sequential odd numbered cylinders followed by the sequential even numbered cylinders (from low number to high number each). Double row radials can be calculated by using a pair of firing order numbers that are either added or subtracted to the number of the cylinder previously fired as is possible.

1-4(O). Why are valves adjusted on a radial engine?

1-4(O). Reciprocating engines with solid lifters or cam followers generally require the valve clearance to be adjusted manually by adjusting a screw and locknut. Valve clearance is needed to assure that the valve has enough clearance in the valve train to close completely. This adjustment (or inspection thereof) is a continuous maintenance item except on engines with hydraulic lifters. Hydraulic lifters automatically keep the valve clearance at zero.

1-5(O). What is the purpose of a master rod and articulating rods?

1-5(O). The master rod serves as the connecting link between the piston pin and the crankpin. The crankpin end contains the master rod bearing. Flanges around the large end of the master rod provide for the attachment of articulating rods. They are attached to the master rod with knuckle pins which are pressed into the holes in the master rod flanges. The master and articulating rod assembly is commonly used on radial engines. In radial engines, the piston in one cylinder in each row is connected to the crankshaft by the master rod. All other pistons in the row are connected to the crankshaft through the master rod via the articulating rods.

1-6(O). What is the purpose, function, and operation of multiple springs on a valve?

1-6(O). The function of the valve springs is to close the valve and to hold the valve securely on the valve seat. The purpose of having two or more valve springs on each valve is to prevent vibration and valve surging at certain speeds. The springs are arranged one inside the other and vibrate at different engine speeds. The result is rapid damping of all spring-surge vibrations. Two or more springs also reduce the danger of weakness and possible failure by breakage due to heat and metal fatigue.

1-7(O). What is propeller reduction gearing and why is it used?

1-7(O). For an engine to develop high power, an increase in crankshaft rotational speed is required. However as propeller tip speed approaches the speed of sound, efficiency is greatly reduced. Propeller reduction gearing is used to allow the engine to turn at a high RPM while keeping the propeller speed lower and efficient. The propeller is geared to the engine crankshaft in such a way as to make the propeller not turn as fast as the engine. There are three common types of reduction gearing: spur planetary, bevel planetary, and spur and pinion.

1-8(O). What is the basic theory of operation of a gas turbine engine?

1-8(O). A gas turbine engine is an internal combustion engine. Like a reciprocating engine, the functions of intake, compression, combustion, and exhaust are all required. The difference is that, in a turbine engine, these functions happen in dedicated sections of the engine and they happen continuously. Air is taken in at the front of the engine and is compressed in the compressor section, either axially or centrifugally. From there it is sent through a diffuser to the combustion section where fuel is discharged and combustion takes place. The energy in the fuel is released and is directed into the turbine section. Turbine wheel(s) extract the energy in the burning fuel. Depending on the engine type, the energy is converted into rotational mechanical energy to operate the engine and create thrust by turning a fan, propeller, or rotor. In turbojet engines, just enough energy is extracted to operate the engine and the remainder is directed out of the exhaust of the engine to be used as thrust.

1-9(O). What are some causes for turbine engine performance losses?

1-9(O). The thermal efficiency of a gas turbine engine is a prime factor in performance. This is the ratio of the net work produced by the engine to the chemical energy supplied in the fuel. The turbine inlet temperature, compression ratio, and component efficiencies are the three most important factors affecting thermal efficiency. Other factors are compressor inlet temperature and combustion efficiency. A high turbine inlet temperature will result in higher efficiency and more power. However, temperature limits must be adhered to or the turbine section can be overheated and destroyed. If the efficiency of the engine components is reduced, then engine performance will reduce. So, damaged or worn components will produce performance losses. Also, if the stagnation density (a combination of airspeed, altitude, and ambient temperature) is reduced, the performance is reduced. This results from the reduced mass of air flowing through the engine.

10-1(O). What is the probable cause of hydraulic lock and how is it remedied?

10-1(O). Whenever a radial engine remains shut down for more than a few minutes, oil or fuel may drain into the combustion chambers or intake pipes of the lower, downward extending cylinders. This is known as hydraulic lock. As the piston moves toward top center in these cylinders, it will collide with these incompressible liquids. Severe damage can be caused. The liquid must be removed to remedy the hydraulic lock and make it safe to start the engine. This is done by removing either the front or rear spark plugs of the affected cylinders and pulling the engine through by hand in the normal direction of rotation. Then the spark plugs are reinstalled and the engine is started.

10-2(O). What checks are necessary to verify proper operation of a reciprocating engine?

10-2(O). A ground check or power check is performed to evaluate the functioning of the engine by comparing power input as measured by manifold pressure with power output as measured by RPM (or torque) and comparing these to known acceptable values. It also includes checking the powerplant and accessory equipment by ear, visual inspection, and by proper interpretation of instrument readings, control movements, and switch reactions. Fuel pressure and oil pressure checks must verify that these pressures are within established tolerances. A cylinder compression test can be performed if it is suspected that there is a problem with valves, pistons or piston rings. A magneto safety check exposes problems with the ignition system. Idle speed and idle mixture checks can also be performed although these relate more to the proper functioning of the fuel system than the engine itself just as the magneto check focuses more on ignition system integrity.

10-3(O). Explain the checks necessary to verify proper operation of propeller systems.

10-3(O). The propeller must be checked to ensure proper operation of the pitch control and pitch change mechanism. The operation of a controllable pitch propeller is checked by the indications of the tachometer and manifold pressure gauge when the proper governor control is moved from one position to another. Each propeller requires a different procedure. The applicable manufacturer's instructions should be followed.

10-4(O). What is involved with the correct installation of piston rings and what results if the rings are incorrectly installed or are worn?

10-4(O). Piston rings prevent leakage of gas pressure from the combustion chamber while lubricating the cylinder walls and reducing to a minimum the seepage of oil into the combustion chamber. Worn or broken piston rings can cause excessive oil consumption and loss of compression. Oil blow-by into the combustion chamber can lead to sticking valves, spark plug misfiring, as well as detonation or pre-ignition due to carbonization of the oil. During installation, the rings are place in the proper grooves facing the correct direction according to the engine manufacturer's instructions. The ring gaps are staggered around the piston. They are compressed with a ring compressor to the diameter of the piston as the cylinder is slid down around the piston making sure that the cylinder and piston plane remain the same. As the cylinder is lowered around the piston with a straight, even motion, it displaces the ring compressor as the rings slide into the bore. Rocking or forcing the cylinder over the piston and rings could cause a ring to escape from the ring compressor and expand or it could crack or chip a ring or damage the ring land.

10-5(O). What are some procedures for inspecting various engine components during overhaul?

10-5(O). There are 3 basic categories of inspection during overhaul: visual, structural non-destructive testing (NDT) and dimensional. The first inspection to be done is the visual inspection. A preliminary visual inspection should be performed before cleaning the parts since indications of failure may often be detected from the residual deposits of metallic particles in some recesses of the engine. Then, parts can be cleaned and visually inspected. Structural inspections can be performed on parts by methods such as magnetic particle inspection, dye penetrant, eddy current, ultra sound, and x-ray as specified by the manufacturer. Finally, using very accurate measuring equipment, each engine component can be dimensionally evaluated and compared to the service limits and tolerances set by the manufacturer.

10-6(O). What are the procedures for reciprocating engine maintenance as they pertain to overhauling an engine?

10-6(O). Aircraft engine maintenance practices, including overhaul, are performed at specified intervals established by the manufacturer. For an overhauled engine to be as airworthy as a new engine, worn and damaged parts must be detected and replaced. This is done by completely disassembling the engine. Visual, non-destructive, and dimensional inspections are performed. The manufacturer publishes inspection criterion and a new minimum and serviceable dimension for all critical component parts. Parts that do not meet these standards must be rejected for use in the engine. A major overhaul of an engine consists of the complete reconditioning of the powerplant. This includes disassembly of the crankcase for access and inspection/rework of the crankshaft and bearings. It is not a major repair and can be performed or supervised by a certified powerplant technician as long as the engine does not contain an internal supercharger or propeller reduction other than spur-type gears. At the time of an engine overhaul, all accessories are removed, overhauled, and tested in accordance with the accessory manufacturer's instructions.

10-7(O). What are some checks necessary to verify proper operation of a turbine engine?

10-7(O). The manufacturer's operating instructions should be consulted before attempting to start and operate any turbine engine. Checking turbofan engines for proper operation consists primarily of simply reading the engine instruments and then comparing the value with those known to be correct for a particular operating condition. Be sure the engine and instrument indications have stabilized. Idling speed must be checked (tachometer) as well as oil pressure and EGT (exhaust gas temperature). Engine pressure ratio (EPR) measures thrust and is used to set takeoff power. It varies with ambient temperature and pressure. Takeoff thrust is checked by adjusting the throttle to obtain a single, predicted, indication on the EPR (engine pressure ratio) gauge. This can be computed from the takeoff thrust setting curve in the operations manual. It can be done at full power or when the throttle is set at the part power stop. If an engine develops the predicted thrust and if all the other engine instruments are indicating within their proper ranges, engine operation is considered satisfactory. On newer aircraft, performance is a function of the onboard computer. FADEC engines have means for checking the engine and displaying the results on the flight deck.

2-1(O). Name two maintenance or inspection tasks performed during routine fuel system inspection and maintenance.

2-1(O). Drain sumps, change or clean filters, check linkages for smooth stop-to-stop operation, check fuel lines for cracks and hoses for deterioration, leak check, check pump operation and motor brush wear, check selector valve for wear, check fuel tanks for corrosion and leaks, check fuel quantity and pressure gauges for proper operation, check vents for obstruction, check function of warning system.

2-10(O). What is the procedure for checking idle mixture adjustment on a reciprocating engine?

2-10(O). To check the idle mixture on a warmed up engine, move the mixture control slowly toward the idle cutoff position. Observe the tachometer for a slight RPM rise (10 - 50 RPM) before the engine cuts out. If this does not occur, adjust the idle mixture until it does.

2-11(O). What are possible causes of poor engine acceleration, engine backfiring or missing when the throttle is advanced?

2-11(O). A lean mixture is the most like likely cause. A cracked distributor block or high-tension leak between two ignition leads can also cause these symptoms and backfiring.

2-12(O). What are three types of fuel metering systems used on reciprocating engine and how do they operate?

2-12(O). Float-type carburetors, pressure carburetors, and fuel injection systems are all used on reciprocating aircraft engines. A float type carburetor uses the volume of air moving through a venturi to cause a suction that meters the fuel. A pressure carburetor uses a closed, pressurized fuel system. The venturi serves only to create pressure differentials that control the quantity of fuel to the metering jet in proportion to the airflow to the engine. The fuel is discharged under positive pressure. A fuel injection system is a continuous flow system that measures engine air consumption and uses airflow forces to control the fuel flow to the engine. Fuel is injected into the airstream on a float type carburetor just before the throttle valve, just after the throttle valve on a pressure carburetor and directly into the cylinder head on a fuel injection system.

2-13(O). Name the fuel metering system components in a float type carburetor.

2-13(O). The main metering system components include the throttle, the venturi, the discharge nozzle, and the float and float valve in the float chamber. The idling system components include the idling jet and the idle mixture adjustment. The mixture control system includes either a needle valve or a back-suction line, the acceleration system including a piston/pump and the economizer system including the economizer needle valve.

2-14(O). What is the purpose of the part power stop on some engines when accomplishing engine trim procedure?

2-14(O). The engine is operated at full power or at the part power control trim stop for a sufficient amount of time to ensure it has completely stabilized. This is usually at least 5 minutes. Follow all manufacturer's instructions.

2-15(O). Explain the operation of a fuel flow indicating system and where it is connected into the engine.

2-15(O). A fuel pressure gauge, calibrated in pounds per hour fuel flow, is used as a fuel flow meter with the Bendix RSA fuel injection system for reciprocating aircraft engines. This gauge is connected to the flow divider and senses the pressure being applied to the discharge nozzles. This pressure is in direct proportion to the fuel flow and indicates engine power output and fuel consumption.

2-16(O). What is the operation of a manifold pressure gauge?

2-16(O). The manifold pressure gauge indicates the pressure in the induction system of a reciprocating aircraft engine. The pressure is measured in the intake manifold downstream of the throttle valve. It is displayed on the flight deck in inches of mercury (Hg) and is directly proportional to the power output of the engine.

2-2(O). What checks of a fuel system can be made to verify proper operation?

2-2(O). A fuel system should have no external leaks. Make sure all units are securely attached. Drain plugs and valves should be opened to clear any water or sediment. The same is true for the filter, screen, and sump. Filter screens and auxiliary pumps must be clean and free from corrosion. Fuel system controls should move freely, lock securely, and should not rub or chafe. Fuel vents must be in the correct position and free from obstruction. Overall engine performance checks give insight into proper fuel system operation. If engine input (manifold pressure) results in the correct power output (engine RPM), the engine performance is acceptable and it is likely the fuel system is operating properly. Check all fuel system related gauges for indications of fuel system operation. Carburetor air temperature, fuel flow, fuel pressure, and cylinder head temperature indications can all indicate potential fuel system problems. An idle mixture check can also be performed.

2-3(O). What is the function and operation of a fuel boost (booster) pump?

2-3(O). A fuel boost pump is designed to provide positive fuel pressure to the engine fuel system. The boost pump forces fuel through the selector valve to the main line strainer. During starting, the boost pump forces fuel through a bypass in the engine-driven fuel pump to the carburetor or fuel injection system. Once the engine driven pump is up to speed, it takes over and delivers the fuel to the metering device.

2-4(O). What is the function of a fuel selector valve?

2-4(O). A fuel selector valve is controlled on the flight deck to select the tank from which tank fuel will be delivered to the engine.

2-5(O). What is done to inspect an engine driven pump for leaks and security?

2-5(O). If booster pumps are installed, they should be energized to check the fuel system for leaks. (During this check, an ammeter can be used to insure all boost pumps pull roughly the same amperage.) The drain lines of the engine drive pump should be free of traps, bends, or restrictions. Check for leaks and the security of the engine driven pump mounting bolts. Check the vent and drain lines for obstructions.

2-6(O). What is the function and operation of engine fuel filters on a turbine engine fuel system?

2-6(O). The function of the engine fuel filters is to remove micronic particles that may be in the fuel so they do not damage the fuel pump or the fuel control unit. Typically, a low-pressure filter is installed between the supply tanks and the engine fuel system. An additional high-pressure fuel filter is installed between the fuel pump and the fuel control. Three kinds of filters are used: micron, wafer screen, and screen mesh. The micron has the smallest particle filtering capability. It requires a bypass valve because it could be easily clogged. Many filters have a bypass indicator. Periodic servicing and replacement of filter elements is imperative. Daily draining of fuel tank sumps and low pressure filters eliminates much filter trouble and undue maintenance of fuel pumps and fuel control units.

2-7(O). What is vapor lock and how can it be avoided or remedied?

2-7(O). Fuel should be in the liquid state until it is discharged in the intake air stream for combustion. Under certain conditions, the fuel may vaporize in the lines, pumps, or other units. The vapor pockets formed restrict fuel flow through the units to the fuel-metering device. The partial or complete interruption of fuel flow is called vapor lock. The three general causes of vapor lock are low pressure on the fuel, high fuel temperatures, and excessive fuel turbulence. Fuel systems are designed to avoid vapor lock. The most significant remedy for vapor lock is the use of boost pumps which pump the fuel from the storage tank to the metering devise under pressure so it cannot vaporize prematurely.

2-8(O). What is a possible reason for fuel running out of a carburetor throttle body?

2-8(O). The float level and fuel level in the float chamber of the carburetor must be below the level of the discharge nozzle or fuel will leak from the nozzle when the engine is not operating.

2-9(O). What are some indications that the mixture is improperly adjusted?

2-9(O). Carbon deposits on the spark plugs and spark plug fouling are signs that the idle mixture is not properly set. Also, faulty acceleration may be an indication of an excessively lean mixture.

3-1(O). What are some indications of a leak in the induction system?

3-1(O). Leaks in the induction system can cause an engine to idle improperly, run rough, or overheat. In severe cases, the engine may not start or may cut out. It also could fail to develop full power. A visual inspection for cracks and leaks should occur during all regularly scheduled engine inspections including ensuring the security of mounting of all components.

3-10(O). Explain the differences between a cascade and a mechanical blockage door thrust reverser.

3-10(O). The two types of thrust reverser systems are the mechanical blockage and the aerodynamic blockage systems. The mechanical blockage system places a removable obstruction in the exhaust gas stream. This is usually done rear of the exhaust nozzle. The exhaust gases therefore are mechanically blocked and diverted at a suitable angle in the reverse direction. The obstruction can be cone-shaped, clamshell-like in appearance or a half-sphere. Since it is directly in the path of the hot exhaust gases, the mechanical blockage type thrust reverser must be able to withstand high temperatures. The aerodynamic blockage type of thrust reverser is used on turbofan engines. Since 80 percent of the forward thrust comes from the fan of a turbofan engine, the aerodynamic thrust reverser redirects the fan air to slow the aircraft. Typically, a translating cowl slides aft and as it does so, blocking panels are deployed into the fan airstream. These redirect the air through cascade vanes that further direct the air forward to slow the aircraft. Since the aerodynamic thrust reverser system deflects fan air, it does not have to be particularly resistant to heat.

3-11(O). What are the hazards of exhaust system failure?

3-11(O). Any exhaust system failure should be regarded as a severe hazard. Depending on the location and type of failure, it can result in carbon monoxide poisoning of crew and passengers, partial or complete loss of engine power, or an aircraft fire.

3-12(O). What are the effects of using improper materials to mark on exhaust system components?

3-12(O). Exhaust systems marked with a lead pencils as well as the use of galvanized or zinc-plated tools must be avoided. The lead, zinc, or galvanized mark is absorbed by the metal of the exhaust system when heated. This creates a distinct change in the molecular structure of the metal. This change softens the metal in the area of the mark causing cracks and eventual failure.

3-13(O). What is the function and operation of a turbine engine exhaust nozzle?

3-13(O). A turbine engine exhaust nozzle directs the exhaust gases. While doing so, it aids in the extraction of power from the engine. A converging nozzle will speed up the gases and extract more thrust. A divergent nozzle will slow the gases and reduce thrust. A nozzle can also help straighten the gases when they exit the turbine or reduce turbulence. A turboprop or turboshaft engine extracts most of the energy for rotating a propeller, rotor blades, or driving accessories such as in an APU. The exhaust nozzle on these engines does little more than direct the gases clear of the aircraft structure since no directional thrust is required. They typically use divergent nozzles or tailpipes. Turbofan engines gain 15 to 20 percent of thrust from the exhaust gases. Therefore convergent exhaust nozzles are common on turbofan engines. Unducted turbofans use two nozzles - one for the fan air and one for the engine core exhaust gases. The fan air exhaust nozzle and the engine core cowling combine to direct fan air aft with as little disturbance as possible using a convergent nozzle shape. The engine core exhaust gases also use a convergent nozzle to extract as much thrust from these gases as possible. Note that the length and opening size of an exhaust nozzle are calculated to ensure the correct gas volume, velocity, and pressure at the rear of the engine.

3-2(O). What are some inspection procedures for ice control systems?

3-2(O). Controlling ice in the induction system of a reciprocating aircraft engine is primarily accomplished by raising the temperature of the induction air. This is done with what is known as carburetor heat. The air intake ducting is equipped with a valve controlled from the flight deck. When opened, warm air that has been circulated around the exhaust system is diverted into carburetor. Carburetor heat should only be used when needed. An excessively hot fuel air charge can result in a loss of power, detonation, and engine failure. Therefore, inspection procedures for this ice control system must include the integrity and free motion of this valve and its control cable. It must fully open and fully close to ensure safe operation. Follow the manufacturer's instruction for lubricating the cable and valve hinge.

3-3(O). Describe the automatic and manual operation of the alternate air valve.

3-3(O). An engine may be fitted with an alternate induction system air inlet that incorporates a dust filter. This type of air filter system normally consists of a filter element and a door that is electrically operated from the flight deck. The pilot opens the door manually with the electric actuator when operating in dusty conditions. Some installations have a spring loaded filter door that automatically opens when the filter is excessively restricted. This prevents the air from being cut off when the filter is clogged with dirt or ice.

3-4(O). What can be done to troubleshoot ice control systems?

3-4(O). An ice control system like carburetor heat is very simple and relatively trouble free. Regular inspection of the ducting, valve, and operating mechanism should reveal any operational problems. When the carburetor heat valve is fully opened, it should only be a matter of a few minutes until the ice is cleared. If this is reported as not being the case, then, if application of the heat was timely, it is likely that the valve is not opening all the way. Check the cable and the valve itself for unrestricted movement and full travel. Any report of low power could be the result of the carburetor heat valve not closing fully. Again, inspect the cable and the valve for proper operation.

3-5(O). Explain how a carburetor heat system operates and the procedure to verify proper operation.

3-5(O). Eliminating ice in the induction system of a reciprocating engine is primarily accomplished by raising the temperature of the induction air. This is done with a carburetor heat system. The air intake ducting is equipped with a valve controlled from the flight deck. When opened, warm air that has been circulated around the exhaust system is diverted into the carburetor. This carburetor heat should only be used when needed. An excessively hot fuel air charge can result in a loss of power, detonation, and engine failure. Therefore inspection procedure for this ice control system must include the integrity and free motion of this valve and its control cable. It must fully open and fully close to ensure safe operation. Follow the manufacturer's instruction for lubricating the cable and valve hinge. If running up the engine on the ground, application of full carburetor heat should be accompanied by a reduction in manifold pressure because the intake air becomes less dense.

3-6(O). What is the cause and effect of one kind of induction system ice?

3-6(O). Fuel evaporation ice is formed because of the decrease in temperature resulting from the evaporation of fuel when it is introduced into the intake airstream at the fuel discharge nozzle. The temperature of the air and components around the evaporating fuel reduces to below freezing and any moisture present becomes ice that settles on the discharge nozzle and nearby structure. This ice builds up and can interfere with fuel flow, affect mixture distribution and lower manifold pressure.

3-7(O). Explain the function and operation of one type of supercharging.

3-7(O). A turbosupercharger or turbocharger system functions to increase manifold pressure on a reciprocating engine. It is an externally driven supercharger that compresses the intake air before it is delivered to the fuel metering device. Engine exhaust gases are directed against a turbine that drives an independent impeller mounted on the same shaft. The impeller compresses the intake air and sends it to the fuel metering device. A controller modulates a wastegate valve in the exhaust stream. The amount of gases directed against the turbine is varied by the position of the wastegate. Thus, the amount of intake air compression is controlled which directly affects the power output of the engine.

3-8(O). Name some indicators of an exhaust leak or methods of detecting exhaust leaks.

3-8(O). An exhaust leak is indicated by a flat grey or sooty black streak on the pipes near the leak. Misaligned exhaust system pipes or components are an indicator that a leak may exist.

3-9(O). Explain thrust reverser system operation and some of the main components.

3-9(O). Without any adverse effect of the engine, a thrust reverser system prevents continued forward thrust of the engine by not allowing the engine fan and/or exhaust airflow to flow aft. Typically, a mechanical blockage or redirection of the air occurs through the use of hydraulic or pneumatic power. When the thrust lever on the flight deck is moved aft of idle, and the aircraft has weight on wheels, a control valve diverts the power to a motor. Through the use of jackscrews, flex-drives, and gear boxes, the reverser mechanism unlocks and deploys to change the direction of the engine outflow. When the aircraft has slowed, the power lever is moved forward and the thrust reverser mechanism stows.

4-1(O). If the ignition switch is place in the OFF position but the aircraft engine continues to run, what is the probable cause of the problem?

4-1(O). The "P" lead is not grounded.

4-10(O). How is the p-lead circuit related to the production of a spark in a magneto?

4-10(O). Current is induced in the p-lead circuit by a rotating magnet. This creates a magnetic field. When the breaker points open the p-lead circuit, the field collapses across the secondary coil windings. This produces a high voltage current that is directed to the spark plug to jump the electrode gap.

4-11(O). What is the difference between a low-tension and a high-tension ignition system?

4-11(O). The low-tension ignition system creates a low-voltage that is distributed to a transformer coil near each spark plug where it is changed to high voltage to fire the plug. A high-tension ignition system uses a secondary coil inside the magneto to create the high voltage which is distributed to every spark plug.

4-12(O). What is the procedure for locating the correct electrical cable/wire size needed to fabricate a replacement cable/wire?

4-12(O). Wire size considerations take into account allowable power loss, permissible voltage drop, and the current carrying capability of the conductor. Allowance must also be made for the influence of external heating on the wire. Replacement wire can be the same wire as the original wire. Wire can be measured with a wire gauge. It can also be found by consulting a table produced by the American Wire Gauge if the circuit load information is known. Additionally, wires often contain identification markings. Consulting the manufacturer's data can reveal exactly which wire is required by deciphering the markings which are typically coded.

4-13(O). What are some installation practices for wires running close to exhaust stacks or heating ducts?

4-13(O). If possible, wires should be kept separate from high-temperature equipment. When wires must be run through hot areas, the wires must be insulated with high-temperature rated material such as asbestos, fiberglass or Teflon. Running coaxial cables through hot area should be avoided. To guard against abrasion, asbestos wires should be in a conduit lined with a high temperature rubber liner or they can be individually enclosed in high temperature plastic tubes before being installed in the conduit.

4-14(O). What procedures must be adhered to when operating electrical system components.

4-14(O). The maximum load from the operation of electrical equipment should not exceed the rated limits of the wiring or protection devices. If loads can exceed the output limits of the alternator or generator, the load should be reduced so that an overload does not occur. If a battery is part of the electrical power system, it should be continuously charged in flight except for momentary intermittent heavy loads such as the operation of a landing gear motor or flaps, etc. Placards should be used to alert flight crews concerning operations that may cause an overload. The total continuous load should be held to 80% of the rated generator or alternator output when assurance is needed that the battery power source is being charged in flight. When two generators are in use, a specified procedure for quick load-reduction should be employed if, for whatever reason, only one generator is functioning and the load must be reduced to that which the single generator can handle without overload.

4-2(O). During an engine run-up magneto check, what is the range of RPM drop considered to be normal when the mag switch is placed in the LEFT or RIGHT position?

4-2(O). 25-75 RPM.

4-3(O). A reciprocating engine either fails to start, fails to idle properly, or has low power and runs unevenly. All of these conditions could be caused by what common defective ignition system part(s)?

4-3(O). Defective or improperly gapped spark plugs.

4-4(O). What can be done to verify if a turbine engine igniter is firing?

4-4(O). The igniter can be heard snapping while rotating the engine or the igniter can be removed from the engine and the spark can be observed while activating the start cycle.

4-5(O). What precautions need to be taken when removing an igniter plug from an engine?

4-5(O). The low voltage lead to the exciter box should be disconnected and wait one minute (minimum) before removing the ignition lead from the plug.

4-6(O). What is the purpose of checking the "P" lead for a proper ground?

4-6(O). A grounded "P" lead disables the ignition and the magneto will not fire. An ungrounded "P" lead results in the ignition being "hot" and movement of the propeller could cause the engine to start.

4-7(O). What are two types of spark plug fouling and what causes each?

4-7(O). Carbon fouling - fuel/air mixtures too rich to burn or extremely lean. Oil fouling - oil past the rings and valve guides into the cylinder. Lead fouling - when using leaded fuel, lead oxide forms during combustion when cylinder temperature is low. Graphite fouling - excessive application of anti-seize compound on spark plug threads.

4-8(O). What are the components in the primary electrical circuit of a magneto?

4-8(O). The breaker contact points, a condenser, and an insulated coil.

4-9(O). What is "E" gap?

4-9(O). The rotational position of a permanent magnet a few degrees past the neutral position where the breaker points are opened.

5-1(O). Name two possible causes of a starter motor that drags.

5-1(O). Low battery, starter switch or relay controls burned or dirty, defective starter, and inadequate brush spring tension.

5-2(O). Name two starter maintenance procedures to keep a starter in proper operational condition.

5-2(O). Replacing brushes and brush springs, surfacing or turning down the commutator, checking the security of the mounting bolts, ensuring the drive gear and the flywheel ring gear are in good condition, and checking the electrical connection for security and corrosion.

5-3(O). What is the purpose for the undercurrent relay in a starter generator circuit?

5-3(O). To open the circuit causing current flow to the motor for its use as a starter so that it can be used as a generator.

5-4(O). What are the sources of air for a pneumatic starter as used on a gas turbine engine?

5-4(O). A ground operated cart, an APU, or, cross-bleed from a running engine on the aircraft.

5-5(O). Why is an air turbine starter cut out after engine self-accelerating speed?

5-5(O). To prevent overspeed since the engine turns at a higher RPM.

5-6(O). Explain the inspection and replacement criterion for brushes on a starter-generator.

5-6(O). Inspection of starter-generator bushes and brush springs is standard starting system maintenance. Typically, brushes are replaced when worn to approximately one-half the original length. Brush spring tension should be sufficient to give brushes a good, firm contact with the commutator. The brush leads should also be inspected to ensure that they are unbroken and that the lead terminal connection is tight.

5-7(O). Explain the operation of a turbine engine starter-generator.

5-7(O). A starter-generator is a shunt generator with an additional heavyseries winding. This series winding is electrically connected to produce a strong field and results in high torque for starting. The starter generator is engaged with the engine at all times. The two-in-one configuration saves both space and weight. To engage the starter, the master switch must first be closed. Then, closing the battery and start switch energizes the starter portion of the unit through an undercurrent relay. As the motor builds up speed, the current draw or the motor begins to decrease. As it decreases to less than 200 amps, the undercurrent relay opens and thus the circuit from the positive bus to the series winding of the starter motor is interrupted. This halts the start operation and the shut generator comes on line.

6-1(O). Name two items to be inspected to ensure adequate cooling of a reciprocating aircraft engine.

6-1(O). Cowling, cowling seals, cowl flaps, cylinder fins, cylinder baffles, and deflector system.

6-10(O). What are the functions of engine oil?

6-10(O). Engine oil acts as a cushion between metal parts and reduces friction. It cools the engine, seals, cleans, and reduces abrasive wear. Oil also prevents corrosion on the inside of the engine.

6-11(O). How can the technician identify and select the proper lubricants?

6-11(O). Aircraft oils are classified by a numbering system that is an approximation of their viscosity. There are different systems in use such as SAE and MIL-spec. Letters, such as a W, are also used to describe the oil or its characteristics. Many factors are considered when determining the proper oil for a particular engine including operating load, rotational speeds, and operating temperatures. In all cases, refer to the engine manufacturer's information when oil type or time in service is being considered.

6-12(O). Name two maintenance actions that are part of servicing an aircraft engine lubrication system.

6-12(O). Periodic oil changes, oil filter change, inspection of oil filter contents, inspection and cleaning of oil screen(s), checking and adjustment of oil pressure relief valve, cleaning oil cooler of obstructions.

6-13(O). What is the reason for changing engine oil at specified intervals?

6-13(O). Oil in service accumulates contaminants such as gas, moisture, acids, dirt, carbon, and metallic particles which reduce the ability of the oil to protect moving parts. Replacing the oil periodically ensure the oil can do what it is designed to do.

6-14(O). What are two reasons for excessive oil consumption on a reciprocating engine that shows no signs of oil leakage?

6-14(O). Low grade oil or improper oil such as ashless dispersant oil used in a new or overhauled engine, failing or failed crankshaft bearing(s).

6-2(O). In what position should cowl flaps be placed for ground operation and why?

6-2(O). Fully OPEN because in this position they provide for the greatest amount of airflow over the engine and thus the greatest amount of cooling.

6-3(O). How is the combustion section of a turbine engine cooled?

6-3(O). Using air that has been drawn through the compressor which is routed through combustion chamber liners that provide a thin, fast-moving film of air that carries the heat away. Air is also routed to join with the burned gases aft of the burners to cool the hot gases before they enter the turbines.

6-4(O). What cools the bearings on a turbine engine?

6-4(O). Air that is bled from the compressor section of the engine and sometimes air that is drawn from outside the engine for cooling purposes is routed to the bearings. Heat is also transferred to the oil that lubricates the bearings.

6-5(O). What would be the effect of removing the engine baffles and seals from around a reciprocating air- cooled aircraft engine and why?

6-5(O). The engine would overheat because the baffles and seals are designed to route cooling air close by and past the engine cylinders and thus draw away heat from the engine.

6-6(O). What are the two common types of heat exchangers used to cool engine oil on turbine engine aircraft?

6-6(O). Fuel oil heat exchangers and air oil heat exchangers.

6-7(O). What is the function and operation of an augmenter cooling system?

6-7(O). The function is to draw ambient air through the engine compartment for better cooling. It is accomplished with augmenter tubes or ejector tubes into which the exhaust gas is directed. This causes a low pressure and increases the flow of ambient air through augmenter and, thus, through the nacelle.

6-8(O). What is the difference between straight mineral oil, ashless-dispersant oil, and synthetic oil?

6-8(O). Straight mineral oil is blended from specifically selected petroleum based stocks. It has no additives except small amounts of pour point depressant and an antioxidant. It is used during the break-in period of a new or recently overhauled engine. Ashless dispersant oil is straight mineral oil with non-metallic, non-ash forming polymeric additives such as viscosity stabilizers. It extends operating temperature range and improves cold engine starting and lubrication during warm-up. It permits flight through a wide range of climactic changes without having to change oils. Synthetic oil is specially formulated and is used in turbine engines. It is more viscous than ashless or straight mineral oil and has a lower tendency to deposit lacquer and coke. It also resists oxidation and has superior load carrying ability. It provides long service life and prevents seal wear.

6-9(O). What types of oils are used for different climates?

6-9(O). Ashless dispersant grades of oil are recommended for aircraft engines subject to wide variations of ambient temperatures. However, below 20 °F, preheating the engine and oil supply tank is normally required regardless of the type of oil used. In all cases, refer to the manufacturer's specifications.

7-1(O). How does a propeller function?

7-1(O). A propeller is essentially a rotating wing. As the engine turns it, the air moving past the curved forward surface of the propeller causes a low pressure when compared to the area on the aft side of the propeller, which is relatively flat. As in a wing, the difference in pressure causes a reactive force in the direction of the lesser pressure. On a wing, this force is upward and is called lift. On a propeller, this force is forward and is called thrust. It is this force that moves the aircraft.

7-2(O). Why are constant speed propellers used?

7-2(O). To obtain maximum efficiency from the propeller by rotating it at a constant speed and to keep the engine RPM constant while adjusting the power output with the throttle lever.

7-3(O). What are the components of a propeller governor and how does it operate?

7-3(O). A typical propeller governor consists of a drive gear to engage the engine, an oil pump, a pilot valve controlled by flyweights, a relief valve system, a piston connected mechanically to the blades, a speeder spring, and an adjusting rack for control from the flight deck. The governor senses the RPM of the engine/propeller assembly via the flyweights. The force of the flyweights is counterbalanced against the force of the speeder spring that is set via the adjusting rack. If the speed of the engine and propeller increase, the flyweight force increases and they move outward. This opens the pilot valve and oil is pumped against the piston. The piston motion transmits the force to the blades which increase pitch angle. At a higher pitch angle, the force of the air striking the blades increases. This increases the load on the engine and serves to suppress engine RPM and keep it constant.

7-4(O). What is a test club propeller? When and why is it used?

7-4(O). A test club propeller is a four-bladed, fixed pitch propeller used during ground testing or break-in of a reciprocating engine. The blades are short and designed to put the correct amount of load on the engine during the test break-in period. The multi-blade design also provides additional cooling airflow

7-5(O). What is the maximum interval between lubrication of a propeller and where does the technician find the proper procedures for lubrication of a particular propeller?

7-5(O). Propellers must be lubricated every 100 hours or at 12 calendar months, whichever occurs first. If annual operation is significantly less than 100 hours, calendar lubrication intervals should be reduced 6 months. Also, if the propeller is exposed to adverse atmospheric conditions, such as high humidity and, salt air, the calendar interval should be shortened to 6 months. The manufacturer's instructions should be consulted for the proper propeller lubrication procedures as well as oil and grease specifications.

7-6(O). How is the angle of a propeller blade measured while the propeller is mounted on the engine?

7-6(O). Propeller blade angle is measure at a blade station(s) specified by the manufacturer. Blade stations are measured in inches from the base of the blade toward the tip. Using a propeller or universal protract placed at the correct blade station, follow the manufacturer's instruction. The angle between the plane of rotation and the propeller blade face at the specified station is what is being measured.

7-7(O). In general, what is the procedure for removing a propeller?

7-7(O). Always follow manufacturer's instruction. In general, remove the spinner dome. Then cut and remove the safety wire on the propeller mounting studs. Support the propeller assembly with a sling. Make an alignment mark on the hub and engine flange to maintain dynamic balance during reinstallation. Unscrew the four mounting bolts from the engine bushings. Unscrew the two mounting nuts and the attached studs from the engine bushings. If the propeller is removed between overhauls, mounting studs, nuts, and washers may be reused if not damaged or corroded. Using care and supporting the weight of the propeller assembly with the sling, remove the propeller from the mounting flange.

7-8(O). What is the function of a typical propeller synchronization system and how does it operate?

7-8(O). Propeller synchronization is used to eliminate the unpleasant beat produced by unsynchronized propeller operation. A typical synchrophasing system is an electronic system. It functions to match the RPM of both engines and establish a blade phase relationship between the left and right propellers to reduce cabin noise. A switch on the flight deck controls the system. When in the "ON" position, pick-ups on each propeller send a signal to a control box. The control box sends a command signal to an RPM trimming coil on the propeller governor of the slow engine to adjust the RPM to equal that of the other propeller.

7-9(O). Explain why is ice a problem for propeller operation. Then, name a means for anti-icing and a means of deicing aircraft propellers.

7-9(O). Ice formation on a propeller blade in effect produces a distorted blade airfoil section and makes the propeller inefficient. Ice collects asymmetrically and produces propeller unbalance resulting in destructive vibration and increased blade weight. A typical propeller anti-icing system includes an on-board reservoir of anti-icing fluid that is pumped to a slinger ring mounted on the rear of the assembly and distributed to the blades by centrifugal force. A typical propeller de-icing system includes electric heating elements adhered to the leading edge of each blade. Power is transferred to the propeller elements through brushes and a slip ring. A timer cycles the elements on and off in sequence or this can be controlled by the pilot.

8-1(O). What procedures are required after the installation of a turbine engine?

8-1(O). After installation, an engine run-up should be performed. On newer engines with electronic engine controls, verification of correct engine instrument indications is required. On engines with hydromechanical fuel controls, the engine must be manually trimmed. This is the process of adjusting the idle and maximum RPM and EPR settings in accordance with temperature and pressure adjusted values provided by the manufacturer.

8-2(O). What are the reasons a turbine engine would require a trim check?

8-2(O). It has a hydromechanical fuel control and the engine or fuel control has just been changed. Also, if the engine is not developing maximum thrust or if there is excessive throttle stagger the engine should be trimmed.

8-3(O). What is the procedure required to adjust (trim) a fuel control unit (FCU)?

8-3(O). Ideally, trimming an engine should be done under conditions of no wind and clear, moisture-free air. Never trim when icing conditions exist because of the adverse effect on trimming accuracy. If there is wind, face the engine intake into the wind to avoid re-ingestion of the exhaust gases. Accurate ambient temperature and pressure readings need to be taken. These are used to compute the desired EPR indication(s) from charts in the maintenance manual. Idle RPM and maximum speed adjustments are made as well as acceleration and deceleration checks according to the specific instructions provided by the manufacturer.

8-4(O). Name three reasons for removal of an engine and what are the required inspections after a potentially damaging event occurs.

8-4(O). Reasons for removal of an engine include: Engine or components lifespan exceeded; sudden stoppage; sudden reduction in speed; metal particles in oil; negative spectrometric oil analysis; operational problems such as excessive vibration; low power output caused by low compression or internal engine deterioration or damage; turbine engine parameters exceeded; and, turbine engine condition monitoring program trends. A sudden reduction does not automatically result in an engine change. Additional test such as a complete visual inspection should be performed - especially of the engine mounts and the nose section of the engine, crankshaft run-out, and oil filter, sump, and screen checks for metal in the oil. If these all prove negative, the engine may be able to stay in service. Also, just the presence of metal in the oil does not mean the engine has to be removed. The quantity and type of metal particles must be further analyzed. Any ferrous metal in an oil screen is cause for concern. Small non-ferrous particles could be normal. A complete oil and filter/screen change should be performed and the engine should be ground-run and filters and screens rechecked.

9-1(O). How would a technician verify proper operation of a fire extinguishing system?

9-1(O). By inspection and good maintenance practices. The fire extinguishing system contains agent containers that must be verified as fully charged by checking the pressure gauge mounted in each bottle against a chart containing temperature-adjusted values. The extinguisher bottle squib, which fires to discharge the agent, has a limited service life and must be changed if the date on the squib has been exceeded. The pressure switch mounted on the bottle sends a signal for an indication on the flight deck when low pressure exists in the bottle due to leakage or discharge. This indication should not be illuminated. An electrical wiring continuity check can also be performed to ensure that power will arrive at the squib when the switch on the flight deck is closed.

9-2(O). How would a technician troubleshoot an engine fire detection system?

9-2(O). A push-to-test button is provided on most fire detection systems. It should light all warning lights and sound the aural alarms. Failure to do so requires further investigation. A faulty test switch or control unit is possible. Also, lack of electric power, an inoperative indicator light, or opening in the sensor element or connecting wiring are possible. Continuity of the sensing element can be checked by measuring the resistance. Intermittent alarms can be traced by visual inspection and moving wires and the sensors in suspected areas to recreate the fault. Also, by disconnecting the sensing elements from the control unit, the fault can be isolated to the sensing elements if the false alarm stops.

9-3(O). What are the basic inspection requirements for an engine fire extinguisher squib and the safety practices and precautions to be followed?

9-3(O). The squib must be inspected to insure it is within its serviceable life. It must be replaced if it is not. The date is stamped on the outside of the squib. Power to the discharge valve assembly should be disconnected when disassembled to access the squib. A discharge cartridge (squib) removed from an assembly should not be used in another discharge valve assembly. The distance that the contact points protrude may vary. The wrong length of protrusion could result in a loss of electrical continuity required to fire the squib and discharge the agent.

9-4(O). What are the components of a typical fire detection system?

9-4(O). There are different types of fire detection systems. All types have some sort of detection device and indication devices on the flight deck. Thermal switch systems are simple and typically will also contain a test switch, test relay, and a dimming relay for the indicator light(s). Thermocouple detection systems contain a control box with relays and a thermal test unit. Optical fire detection systems contain an amplifier and comparative circuits to decipher sensing data. Continuous loop systems also contain control boxes which decipher the analog signal from the sensor loops and signal warnings or supply the Aircraft In-flight Monitoring System. The most sophisticated systems contain a control module that uses control cards with various interpretive circuitry to decipher signals from each area where sensors are located. Some systems will initiate extinguishing automatically from the control module.

9-5(O). Maintenance procedures for fire detection systems include extensive visual inspection of the components. Name three common items to look for on a visual inspection of a fire detection system.

9-5(O). Cracked or broken loop sections, abrasion of elements by rubbing, loose metal that might short a spot detector, condition of rubber grommets and mounting clamps, dents and kinks in loop elements, secure connections at the end of the sensing elements, integrity of shielded leads, and, proper routing and support of elements.