RECIP ENGINES

What is the purpose of dynamic dampers on crankshafts?

Reduce vibration

What types of bearings are found in reciprocating engines?

Plain, ball and roller bearings

Are the connecting rods used in each cylinder of a radial engine the same? Explain.

No, it has master and articulating rods

Name the different types of piston rings.

Compression, oil control, oil scraper

Where should piston rings gaps be installed relative to each other? Why?

Compression rings gaps should be installed staggered to prevent excessive blowby

What could result from incorrectly installed piston rings?

Excessive oil consumption / blowby

What purpose do oil control rings serve?

Controls layer of oil on cylinder walls

What is used to prevent valve surge or floating in an aircraft engine?

Two or more springs on each valve

On engine equipped with hydraulic valve lifters, what should the running valve clearance be?

Zero

What is the purpose of valve overlap?

Better volumetric efficiency and lower cylinder operating temps

What is the main advantage of horizontally opposed engines over a radial engine?

Smaller frontal area and less drag, no hydraulic lock

How many throws are in the crankshaft of a six cylinder horizontally opposed engine?

6

What material are piston rings made of?

Cast iron or chrome plated steel

What is the reason for using hydraulic lifters in an aircraft engine?

To eliminate valve clearances during operation and reduce component wear

What speed does camshaft turn relative to crankshaft speed?

Half the speed

What kind of main bearings are used in a horizontally opposed engine?

Steel backed, lead-alloy inserts - Plain bearings

What stroke is the piston of a recip engine on when the intake begins to open?

Exhaust

What stroke is the piston of a recip engine on when exhaust valve begins to open?

Power

Why are hot and cold valve clearances given for radial engines?

Because of the expansion of the large engine / expansion coefficients

What is a cam-ground piston?

Piston made out of round that expands to be round at operating temperatures

Where is the piston when ignition occurs?

Typically, around 30 degrees before top dead center on the compression stroke

What is a full floating wrist pin?

Pin that allows full movement between the connecting rod and piston

Would excessive valve clearance cause valves to open early or late?

Late

Why are some valves filled with metallic sodium?

For cooling purposes

What causes detonation in an engine?

Excessive heat or pressure causing an uncontrolled explosion in the cylinder

What is meant by compression ratio of an engine?

The ratio between cylinder volume at BDC vs at TDC

RECIP ENGINE OPERATION, INSTRUMENTS, MAINTENANCE, OVERHAUL

What indications are given in the event of a leaking or open primer while the engine is running?

Will not idle properly

A cold cylinder is found when troubleshooting a running engine, what does this indicate?

No combustion in that cylinder

When pulling a propeller through, a hissing sound is heard indicating valve blow-by. What procedure should be done next?

A compression check to determine leaking cylinder

What is the purpose of a compression test?

Ensure that valves and piston rings are sealing properly

When an engine is overhauled, how is its history affected? When its rebuilt how is its history affected?

Overhaul, not affected. Rebuilt, if done by manufacturer it is granted zero time.

What inspections should be performed after a propeller strike without sudden stoppage?

Engine mounts, crankcase, engine oil and screens, crankshaft runout

Name some of the precautions that should be performed prior to engine removal.

Disconnect battery, turn off fuel, chock wheels, add tail stand

When inspecting a piston, where are cracks most likely to be found?

In highly stressed areas like piston bosses and ring lands (ring grooves)

What does it mean if an engine part is within “serviceable limits”?

That it is still within spec to be used and doesn’t need replacement

What tool or instruments are used to inspect a cylinder barrel for out-of-roundness?

Inside micrometer or telescoping gauge with an outside micrometer

How can a loose stud in an engine crankcase repaired?

By removing, inspecting threads for damage and installed oversize stud or helicoil insert

What publication is used to check an engine for normal operation?

Manufacturer maintenance manual

A weak cylinder is found during a compression check, what must be inspected?

Inside of the cylinder, piston rings and valves

What purpose does an oil analysis serve?

Indicates metal wear in oil and establishes trends

What inspection should be performed on an engine that has been in storage?

Inspection to check for corrosion

Where would a carburetor air temperature bulb be located?

In the ram air intake

What is a fuel pressure range on float-type carbs?

3-5 PSI

Name the basic components of a fuel indicator system.

The fuel transmitter and indicator

What unit of measure generally indicates fuel flow?

Gallons per hour or pounds per hour

Why is fuel flow monitored?

To indicate fuel left, flight time left and engine performance

What does the manifold gauge indicate and how is it calibrated?

Absolute pressure inside manifold in inches of mercury or “HG

What directly controls manifold pressure?

Throttle position and engine RPM

During engine operation, where should the propeller control be set when checking the manifold

pressure?

Low pitch, high RPM

Is the aircraft electrical system required to furnish power to a cylinder head temperature gauge?

No, thermocouples don’t need external power

What are the possible indications of an oil pressure transmitter or indicator malfunction?

Severe or sudden drop in pressure with no change in oil temp or oil supply

What does a tachometer indicate on a recip engine?

Engine RPM

Where should the thermocouple be installed on a reciprocating engine using a single probe cylinder head temperature system?

On the hottest cylinder

TURBINE ENGINES

Explain the main difference and advantage of using a turbojet vs a turbofan engine.

A turbofan engine has a bypass duct that allows for more thrust to the amount of fuel burnt

Name the major components in a gas turbine engine.

Inlet, compressor, combustor, turbine, exhaust, gearbox, accessory section

What determines the amount of airflow through a turbine engine?

Speed of aircraft, air density and compressor speed

Name the two types of compressors used in turbine engines.

Centrifugal and Axial-flow compressors

Name two different methods of attaching turbine blades to the disk.

Dove-tail, fir-tree, bulb-type (Blisk might also be accepted)

What is a split compressor system?

A dual spool or twin spool uses two shafts spinning freely of each other connected to different turbine and compressor stages.

What are the different types of combustion chambers used in turbine engines?

Can, annular, can-annular (and reverse flow annular)

What prevents combustion chambers from burning?

Cooling air along the inside of the liner

What is the purpose of the interconnecting tubes attached between can type combustion chambers?

For flame propagation between cans

What functions do axial flow turbine nozzles perform?

Direct airflow to drive the turbine rotor at a specific angle
How is thermal stress relieved on a turbine disk?

By directing bleed air onto the disc face or grooves cut into the disc.

What are carbon seals used for in a turbine engine?

Oil seals for rotor shaft bearings

What is shaft horsepower?

Indication of torque being developed by a turboprop or turboshaft engine

Name the main components of a typical APU.

APU turbine engine, load compressor for bleed air and an electrical generator

When is the greatest demand placed on an APU?

When supplying bleed air

How is an APU generally started?

An electric starter and battery power

Where does the APU get its fuel supply?

From the aircrafts main fuel tanks

At what speed does a gas turbine APU operate and how is the speed maintained?

At or near rated power regardless of load. Fuel control keeps speed relatively constant

What is used to prevent a heavily loaded APU from exceeding maximum EGT?

A load control valve controlling pneumatic loads imposed on APU

How is an APU shut down and why is that procedure used?

APU load is taken off and then allowed to run for a cool down period before shutting off. Prevents thermal shock or damage of APU

What powers the variable inlet guide vanes used on some turbine engines?

Fuel pressure

What is fan blade shingling?

When shrouds overlap

When a turbofan or turbojet engine is shut down, what should a mechanic listen for during coast down?

Obvious noises of grinding/rubbing or unusual sounds

What are the two basic sections of a turbine engine?

Hot section and cold section

What is the purpose of the stators in an axial flow compressor?

To convert velocity into pressure

How many igniters are typically used in a turbine engine?

Two

What is a free turbine turboshaft engine?

A turbine engine where the output shaft rotates independently of the turbine driving the compressor for the engine

What kind of bearings support the rotor shaft on turbine engines?

Anti-friction bearings like ball or roller bearings

Where are the repair limits for compressor blades of a turbine engine found?

The overhaul manual

Why must a turbine engine be allowed to cool down period before shutdown after operating at high temperature?

So that the shell doesn’t shrink around the core and seize the rotor

What is a hung start in a turbine engine?

When the engine ignites but fails to reach self-accelerating speed

What is a hot start in a turbine engine?

When the EGT exceeds limits during starting

What is meant by creep of turbine blades?

Elongation of turbine blades due to normal operation or overspeed and overtemperature conditions

Where is water injected into a turbine engine for cooling purposes?

At the compressor inlet or engine diffuser

At what point in a turbine engine is temperature the highest?

Inlet to the turbine section

TURBINE ENGINE OPERATION, INSTRUMENTS, MAINTENANCE, AND OVERHAUL

Why are compressor washes performed and what methods are commonly used?

To remove contaminants and maintain satisfactory performance. Fluid wash and grit blast are commonly used (Fluid wash can be expanded to desalinization wash and emulsion wash)

How can you tell if a turbofan or turbojet engine is out of trim?

Will have a high exhaust gas temperature at rated engine pressure ratio for takeoff power

Name the different types of compressor blade damage that may be found during inspection

Scratches, gouges, pitting, dents, galling, burrs, burns, cracks

What kind of markers can be used to mark parts in hot and cold sections during repairs?

Felt tip marker, layout dye or chalk

How does relative humidity affect turbine engines?

Negligible effect

What criteria determines replacement of life limited parts on a turbine engine component?

Cycles, hours and/or calendar time

If turbine blades are removed from a turbine disk, why should they be reinstalled in the same place?

To maintain proper turbine wheel balance

How are gas turbine engine tachometers calibrated?

In percent of RPM

On a turbine engine, what is the engine pressure ratio and what does it indicate?

Pressure ratio between compressor inlet and turbine outlet. Indicates thrust being produced

On a turbine engine, what does exhaust gas temperature indicate and how is it obtained?

Relative indication of turbine inlet temperature. With thermocouples installed on engine

Can the EGT system on a turbine engine be checked without running the engine?

Yes, by checking resistance of the thermocouple circuit

ENGINE INSTRUMENTS

Where does the manifold pressure gauge pick up pressure it measures?

In the engine intake manifold

What are the two types of pickups used for measuring cylinder head temperature in a recip?

The bayonet type thermocouple threaded into the cylinder or the washer type that acts as the spark plug washer

Why do most oil pressure gauges have a restrictor in line between the engine and instrument?

Dampen pulsations and provide a consistent reading

What is used to measure fuel flow of a fuel injected recip engine?

Pressure drop across the nozzles

What is the indication if the needle of a ratiometer type oil temperature gauge pegs to the high side of the dial as soon as the master switch is turned on?

There is an open in the circuit seeing infinite resistance

What type of indicating system is used to measure exhaust gas temperature in a turbine engine?

Thermocouples located evenly around the engine

What should a thermocouple type cylinder head temperature indicator read when the engine is not operating?

Ambient temperature

How does a torquemeter actually measure the torque produced by an engine?

By the amount of twist measured at two ends of a rod or oil pressure gauge

What two pressures are measured to get the engine pressure ratio of a turbojet engine?

Compressor inlet and turbine outlet

What two materials are thermocouples made of in a turbine exhaust gas temperature?

Chromel and Alumel

What kind of mechanism is normally used to measure oil pressure in a recip engine?

Bourdon tube

What is measured by the tachometers of a two-spool gas turbine engine?

The individual speeds of each spool

Does the tachometer of a geared recip engine indicate the crankshaft RPM or propeller RPM?

Crankshaft speed

INDUCTION SYSTEMS

Name the three components of an induction system on a recip engine.

Air scoop, fuel metering device, intake manifold

What could happen if the induction system becomes obstructed?

Reduced power or may not run at all

How does induction icing affect engine performance?

Causes reduction in power and possible erratic operation

How is induction ice categorized?

Impact ice, throttle ice, Fuel evaporation ice

What is the common method used to prevent induction system ice in a recip engine?

Raise temperature of intake air with a preheater

What causes fuel evaporation icing?

Because of the decrease in temperature due to the fuel evaporating in the air

Is carb ice more likely to occur at a higher or lower power setting? Why?

Lower because throttle is partially closed offering bigger area for ice accumulation

What may be the indication of leaking intake pipes?

Runs rough at low RPM

What happens to engine power when carb heat is applied?

Reduced power

What could happen if carburetor heat is applied at high engine power settings?

Detonation

What are the two types of supercharged induction systems?

Internally driven and externally driven

How and at what point does an internally driven supercharger boost air pressure?

When the engine driven impeller compresses the air fuel mixture after the carburetor

What is used to power a turbocharger?

Exhaust gas onto a turbine wheel

What could result if the wastegate on a turbocharger system does not fully close?

Unable to create rated power

What function does a turbocharger waste gate perform?

Controls amount of airflow directed to or around the turbocharger

What could cause a turbocharged engine to surge?

Waste gate or controller malfunction

What are the most common ways to control a waste gate?

Linkage to throttle, separate control, actuator off of oil pressure

In a pressurized recip engine, what component in a turbocharger system is used to limit the amount of turbocharger airflow going into the cabin for pressurization?

Sonic venturi

What is the function of the divergent shaped jet engine inlet during subsonic flight?

Increases air pressure and reduces velocity

Where are bell mouth inlet ducts typically found?

Helicopters

How do venturi type particle separators, found on many turbine aircraft, function?

By using a venturi to speed up air, inertia is imparted on particles and is routed past the engine

What are the most common methods used for anti-icing of a turbine engine inlet duct?

Electrically or with bleed air

Where is heat taken from that is used to heat induction air for recip engines?

From a heater muff around the exhaust

Where does alternate air come from on pressure carb or fuel injection systems?

From inside the engine cowling

Where does carb ice normally form in a carburetor?

Throttle valve

Why do some turbine engines use variable inlet guide vanes?

To provide the best efficiency for each RPM

What is usually installed between a turbocharger and a carburetor?

An intercooler

How does an engine inlet vortex destroyer help prevent FOD ingestion to the engine?

By directing bleed air down in front of the engine to prevent formation of the vortex

EXHAUST

What is the purpose of the exhaust system?

To remove high temperature noxious gases

Name the two types of recip exhaust systems.

Short stack and collector type

What drawback in collector systems is more then offset when used a turbocharged engine?

Reduced power from higher back pressure

What could result if the internal baffles or diffusers in an exhaust system fail?

Increased back pressure resulting in lower power

What type of exhaust system is used in turbocharged engines?

Collector system

What kind of material is normally used to make baffles and diffusers of an exhaust system?

Stainless steel

How do you inspect internal baffles and diffusers of an exhaust system?

Disassembly and visual inspection

Why is an exhaust system failure considered a severe hazard?

Because of carbon monoxide poisoning, loss of power or fire hazard

What could happen in lead, zinc or galvanized marks are made on an exhaust system?

Change in molecular structure leading to cracks

What happens if the heat exchanger leaks exhaust gasses into the induction system?

Loss of engine power

What is an indication of an exhaust gas leak?

Black or gray sooty deposits near leak

Where are the most common places to find cracks in an exhaust system?

At welds, clamped areas and flanges

What is a common cause of turbocharger wastegate sticking?

Carbon buildup

Why are turbocharged exhaust system leaks very damaging at high altitudes?

The pressure differential causing leaks with torch like intensity

What are exhaust system coke deposits?

Excessive carbon buildup

What is the result of changing the exhaust nozzle area of a turbine engine?

Engine performance and exhaust gas temperature change

Name the components of a typical turbine exhaust nozzle.

Tail cone, duct and strut supports

What is the purpose of a thrust reverser?

To aid in braking after landing

How does a noise suppressor found on older turbojet engines work?

By converting low pitch noise to high pitch noise that doesn’t travel as far

What are the most commonly used types of thrust reversers?

Mechanical clamshell and aerodynamic cascade types

How much thrust do thrust reversers typically produce compared to engines forward thrust?

Significantly less

What are the hazards of operating some thrust reversers at low ground speeds?

FOD ingestion, exhaust gas reingestion

How does a power recovery turbine increase the power of a recip engine?

By use of an exhaust gas driven turbine through a fluid coupling

How tight should the clamps be tightened that hold sections of exhaust systems together?

Loose enough to permit some movement and not damage the exhaust when its heated

What is the purpose of ball joints and bellows used in the exhaust of a recip engine?

To allow some expansion without leaks

Why do some supersonic aircraft use a convergent-divergent exhaust duct?

To increase the velocity of the gas into the supersonic range

What type of damage is often found in the hot section of a turbine engine?

Cracks

ENGINE FUEL AND FUEL METERING

What are some of the sources used to heat fuel in a turbine engine fuel system?

Bleed air or oil

What are the most common types of fuel metering systems used on small reciprocating engines?

Float type carbs, pressure type carbs, pressure injection systems

What function does the mixture control perform?

Controls the air fuel ratio

What generally causes spark plug fouling?

Rich operation at idle speeds

What is the purpose of the accelerating system?

Provides immediate but brief increase in the fuel/air ratio

What is a carburetor economizer system?

Enrichens the mixture at high power settings for increased cooling

When mixture is placed in idle cutoff, a slight rise in RPM is noted prior to deceleration. What does this indicate?

Correct idle mixture setting

Why should engine RPM be accelerated periodically when making carburetor adjustments?

To clear the engine

What maintains the fuel pressure in a pressure injection carburetor?

Engine driven fuel pump

What happens if the manual mixture control of a pressure injection carburetor is moved to the idle cutoff position?

The engine stops

How does an automatic mixture control (AMC) system function?

Uses sealed bellows that expand and contract with altitude to control mixture

What are some of the advantages of a fuel injection system of carburetor systems?

Better acceleration, better fuel distribution, better fuel economy, less induction icing, reduce overheating of individual cylinders

What purpose do turbine engine fuel control units serve?

Automatically meter fuel in the engine

What are the two basic types of turbine engine fuel control units?

Hydromechanical and electronic

What are the engine variable detected by the fuel control unit?

Power lever position, engine RPM, inlet temperature, inlet pressure, turbine exhaust pressure, burner pressure

What are the two major components of a supervisory electronics engine control?

Electronic control and hydromechanical unit

What are some of the advantages of a full authority digital engine control (FADEC)o over a hydromechanical fuel control?

Better fuel economy, improved starts, automatic engine trimming, engine limit protection, controls tip clearance between case

What do turbine engine fuel spray nozzles do?

Inject fuel into the combustion area

What are the different engine indications used for trimming a turbine engine?

EPR or RPM depending on engine

What maintenance adjustments are normally allowed on an installed hydromechanical fuel control?

Idle RPM, Max RPM or EGT, fuel specific gravity

What type of pump can vary the amount of fuel discharged regardless of speed?

Centrifugal type pump

What is used to keep water, sediment, and foreign matter out of the carburetor?

Main fuel strainer

What is the purpose of a pressure relief valve in a constant displacement pump?

To allow excess fuel back to the inlet side of the pump

What type of engine driven pump is widely used other then gear or piston type pumps?

Rotary vane type

What function do fuel boost pumps perform?

Provide pressurized fuel to the engine driven pump. Reduces vapor lock and cavitation

What is a commonly used type of fuel boost pump?

Centrifugal type

What causes vapor lock and why is it of concern?

Insufficient pressure, high temperature and excessive turbulence. May block flow of fuel to the engine

What function does the engine driven pump on a turbine engine perform?

Provides pressurized fuel to the engine

Name the two categories of turbine engine pumps.

Constant and variable displacement

What category is a gear type pump classified in?

Constant displacement

When performing an external inspection of an engine driven fuel pump, what should you look for?

Leaks and security of mounting

What is the purpose of a shear section of the driveshaft in a dual element constant displacement pump?

So that if one element seizes, shaft will shear and the other element may still operate

Where in a turbine engine fuel system is ice formation likely to occur and how is it prevented?

Fuel filter is most susceptible to icing. Prevent with use of a fuel heater

What is the purpose of a bypass valve in an engine fuel system micron filter?

If the filter clogs fuel can still flow to the engine

What is the purpose of a duplex fuel nozzle?

Provide two spray patterns for different power settings

What are the functions of the pressurizing and dump portions of a pressurizing and dump valve?

Pressurizing valve provides fuel to the primary and secondary nozzles, dump valve allows fuel to drain after engine shutdown

What purpose do fuel selector valves serve?

To allow tank and engine selection and provide fuel shutoff

What are the two locations where water may be injected into a turbine engine?

Compressor inlet and diffuser section

What is a duplex fuel nozzle in a turbine engine?

A fuel nozzle with 2 spray patterns

What is the function of a float carburetor?

To meter the fuel of a reciprocating engine and vaporize it into the airstream

Does the fuel/air ratio become leaner or richer as the aircraft goes up in altitude?

Richer due to lower air density

Does the fuel/air ratio become leaner or richer when carb heat is applied?

Richer due to lower air density

What would happen to the fuel/air ratio in a float type carb if the main air bleed becomes clogged?

Excessively enriched mixture

What are the two purposes of a manifold valve (or flow divider) in fuel injection systems?

To evenly divide the fuel to each nozzle and provide fuel shutoff point close to the nozzles

How does the mixture controls change the fuel/air ratio in a Teledyne continental injection system?

By varying the amount of fuel going to the flow divider and returning to the fuel pump inlet

Why must diaphragms of a pressure carb be soaked before carb is ready for flight?

To restore condition of flexibility when it was calibrated

How does EGT of a recip indicate the fuel/air ratio being burnt by an engine?

Temperature changes with the fuel/air ratio being burnt in a cylinder and can be interpreted by the EGT

What two things can be adjusted when adjusting idling of a recip engine?

Idle speed and idle mixture

What is controlled by the adjustment of the orifice in the fuel pump of a Teledyne continental injection system?

The high unmetered fuel pressure

What is the significance of the letters stamped on flats of fuel injection nozzles?

It indicates the fuel flow rating of the nozzle (Lower letter, smaller fuel nozzle)

What is the function of the derichment valve in a pressure carb used on engines with antidetonation injection systems?

Leans mixture when ADI fluid is flowing. Returns to normal mixture when ADI stops

What position is the mixture control in for starting of an aircraft engine with a pressure carb system?

Idle cutoff position

What position is carb heat in for starting a recip engine?

Cold position

Why is an aircraft recip engine killed by placing mixture in idle cutoff instead of with magneto switch?

So that there is not excess fuel still available and an accidental start is less likely

Where is the fuel in a continuous flow injection system discharged?

At the ports of the cylinders

What direction relative to wind should a turbine powered aircraft be positioned when fuel is being trimmed?

Generally, into the wind

What engine parameters are sensed by the fuel control unit of a turbine engine?

Engine RPM, inlet and outlet pressures, power lever position, inlet air temperature and turbine outlet temperature

When does the acceleration system operate on an aircraft carb?

Under rapid acceleration

What is the purpose of the bypass valve in an engine driven pump?

If the engine pump fails it allows fuel to flow past it

Which side of the firewall is the engine fuel shutoff valve?

Side opposite of the engine

What are three purposes for boost pumps in a fuel system?

Prevent vapor lock, provide fuel for starting the engine, transfer fuel between tanks

What kind of pumps are often used as boost pumps?

Centrifugal type

What is meant by a compensated relief valve in an engine driven pump?

A relief valve that will off seat at pressures proportional to the ambient pressure

What are the two basic types of turbine engine fuels?

Jet A / Jet A1 - Kerosene. Jet B – Kerosene/gasoline

What are the two reasons ‘Prist’ is used in turbine engine fuel?

To prevent microbial growth and lower the freezing temperature

Why do some aircraft fuel filters have a built-in relief valve?

So if the filter becomes clogged fuel can still flow to the engine

ELECTRICAL, STARTING, IGNITION

• How can the remaining service life of starter generator brushes be determined?

  • Visual inspection for wear groove on brushes

• What components of the starter generator require periodic inspection?

  • Brushes and commutator

• Between field and armature windings in starter generators, which ordinarily receive current for operation in the start mode?

  • Both windings receive power for starting

• What are the possible sources of low pressure compressed air used for starting jet transport aircraft equipped with air turbine starters?

  • Ground power unit, APU or compressed bleed air from another engine

• When should ignition ideally occur?

  • Before the piston reaches top dead center on the compression stroke, determined by the manufacturer

• Why are dual magnetos used in the engine ignition system?

  • For better power and redundancy

• Why is magneto timing so important?

  • Because it allows for proper engine operation. They must be internally timed to produce the correct strength spark and to the engine to prevent kickback or reduced power.

• What function does a magneto perform?

  • Produces high voltage to jump the spark plug gap for ignition

• Name the components of a high-tension magneto system?

  • Permanent rotating magnet, soft iron core and pole shoes, coil, cam, breaker points, condenser(capacitor), distributor

• Name the three main circuits of a high-tension magneto system?

  • Magnetic, primary electric and secondary electric

• What is an E-gap angle?

  • A number of degrees after neutral where greatest magnetic stress exists

• What reduces arcing in the points and also aids in the collapsing of the magnetic field in a magneto?

  • A capacitor

• How does a magneto produce the high voltage required to fire a spark plug?

  • Spinning magnet induces electricity into primary circuit, points open at E-gap and high voltage is induced into the secondary coil for the spark plug

• What is the P-lead and how does it function?

  • Connects to the ignition switch to turn the magnetos off by grounding the P-lead

• What is a magneto timing light used for, and what does it indicate?

  • For internal timing of the magneto and timing to the engine. Indicates points are open

• Why are turbine engine igniters generally not susceptible to carbon fouling?

  • High intensity spark cleans the firing end

• What is the function of a duty cycle in relation to a turbine engine ignition system?

  • Duty cycle describes a specific time something can operate before a required specific cool down time is required. Some turbine ignition systems may have a duty cycle rating to be adhered to

• What are the three main components of a turbine engine ignition system?

  • Exciter, igniter, high tension leads

• When the engine is operating, what does an ammeter / load meter indicate when connected to: 1. Battery positive lead. 2. Generator output lead?

  • Battery positive indicates if the battery is being charged is discharged, generator indicates how much is being generated by the generator

• What is done to ensure that each generator shares the load in a multiple generator system?

  • Generators must be paralleled

• Where would you find generator load ratings and performance data?

  • On the data plate of the generator

• How is the voltage of a DC generator controlled?

  • By varying strength of the magnetic field

• What is the most common type of alternator used in most aircraft AC systems?

  • Three phase alternator

• How does a voltage regulator control the voltage of an alternator?

  • By controlling voltage of DC exciter / controlling magnetic field strength

• What does the speed of rotation and number of poles of an alternator determine?

  • Frequency of alternator output

• What are some of the methods used to maintain 400 hertz alternator output frequency on large turbojet or turbofan engines?

  • Constant speed drive units, Integrated drive generators and variable speed constant frequency power systems

• Name the major parts of a DC motor?

  • Rotating armature, field coils, brush assembly, frame

• Name the components of a direct cranking electric starter system?

  • Motor and an automatic engaging and disengaging mechanism. Some may also have reduction gearing

• Name three types of DC motors?

  • Series wound, shunt wound, compound wound

• What type of DC motor is commonly used for a recip engine starter and why?

  • Series wound, it has a high start torque

• What are the operating modes of a turbine engine starter generator?

  • It operates as a motor to start the engine and once started functions a generator

• What is a possible indication when a starter drags?

  • Dirty or worn commutator

• Where would wire with high temperature insulation material be used?

  • Anywhere where high heat is to be expected, like around exhausts and heat ducts

• What is the size standard for electrical wire used in US manufactured aircraft?

  • American Wire Gauge (AWG)

• How are the wire sizes represented?

  • By AWG with smaller numbers being larger wire

• What is the maximum slack allowed between the supports of a single wire or bundle installation?

  • 1/2”

• Why are wires bonded on powerplant installations?

  • To provide current return paths for accessories and prevent static discharge

• Why is stranded wire used rather than solid wire in most powerplant electrical systems?

  • Solid wire is more likely to break or crack with vibration

• What two things must be considered in selection of wire size when making an electrical installation in an aircraft?

  • Amperage and distance of circuit

• Why are some wires in installations twisted together?

  • To help cancel out magnetic fields generated by the conductors

• What is used to protect a wire bundle from chafing where it passes through a hole in a bulkhead or frame?

  • Grommets

• How are electrical wires protected where they pass through areas of high temperature?

  • With conduit or high temp insulation

• What is the minimum separation allowed between a wire bundle and fluid line carrying combustibles or oxygen?

  • 6 inches

• What is the significance of the color of solderless connectors used on electrical wires?

  • Indicates gauge size range of the connector

• What is the maximum number of wires that can be stacked on a single stud in a terminal strip?

  • 4

• What is the purpose of shielding used to encase some electrical wirings?

  • Prevents radio interference by grounding intercepted electromagnetic fields

• Why must a switch be derated if used in a circuit controlling a DC motor?

  • Because of the high start current

• What is used as a rectifier to produce direct current in a DC generator?

  • Commutator and brushes

• How does a vibrator type voltage regulator control the output of a DC generator?

  • Strength of the field is proportional to output voltage, points open when voltage too high, so then a resistor is in series. Lowers voltage. Switch vibrates open and close to regulate voltage.

• What is meant by paralleling generators in a twin engine aircraft?

  • Setting the generators to have equal electrical load

• What is meant by flashing the field of a DC generator?

  • Restoring residual magnetism in the frame

• What kind of rectifier is used in a DC alternator of the type that is used on most of the modern light airplanes?

  • Full wave three phase rectifier

• What three things must be synchronized before a three phase AC generator is connected to a bus being served by another generator?

  • Frequency, voltage output, phase rotation

• What must be done to reverse the direction of rotation of the armature of a DC electric motor?

  • Reverse direction of power thru armature or field coils. Not both

• What aircraft circuit does not normally contain a fuse or circuit breaker?

  • The starter circuit

• When removing a battery, which connection should be removed first?

  • Negative

• What is meant by effective voltage of sine wave alternating current?

  • The value of alternating current effective to produce same amount of heat as DC

• When should wiring be installed in a conduit?

  • When going thru high heat areas, areas where wire may be easily chafed or where they may be easily grabbed by personnel

• What is the main advantage of a magneto ignition system?

  • It generates its own electricity and isn’t reliant on the system power

• What is the function of the capacitor in a magneto?

  • To minimize arcing of the points, speed up collapse of magnetic field

• What is a compensated cam in a magneto and what engine type is it used?

  • Used in radials to spark at same linear distance from TDC on each cylinder

• What is the significance of the numbers on the distributor of an aircraft magneto?

  • Firing order of the magneto

• What happens when the ignition switch is placed in the off position with a magneto?

  • The P-lead should become grounded

• What is the primary reason for having a low-tension ignition system on some aircraft?

  • Used for high altitude where flashover is a problem

• What is the basic difference between a low-tension and high-tension magneto?

  • High tension has high voltage from the magneto to cylinder. Low tension has low voltage and steps up at the cylinder

• What is meant by an All-Weather spark plug?

  • Has a rubber grommet to form a watertight seal

• What is meant by reach of a spark plug?

  • How many threads are on the spark plug to go into the cylinder

• What is the difference between a hot spark plug and cold spark plug?

  • The ability to transfer heat to the cylinder

• What is checked when a magneto is internally timed?

  • That the points open at E-gap and that the distributor is installed in the correct position

• What is the purpose of a vernier coupling used on magneto drives?

  • To allow for exact adjustment of magnetos on radial engines

• What is the advantage of fine wire spark plugs over massive electrode spark plugs?

  • Firing end is more open which allows gases to escape and preventing lead contamination

• Why is it important that the spark plugs be kept in numbered holes in a tray when they are removed?

  • Because they can indicate how that cylinder operates and rotation of spark plugs

• What is the purpose of staggered ignition timing between magnetos?

  • To account for the diluted mixture near the exhaust valve

• What position should the ignition switch be placed when using a timing light on magnetos?

  • BOTH

• Why is it important to use a torque wrench when installing a spark plug?

  • If too loose, may not seal correctly. If too tight may crack or strip threads

• Why are pressurized magnetos used on most recip powered aircraft that operate at high altitudes?

  • To prevent arcing internally from less air being less of an insulator

• What type of ignition system is used on most turbine engines?

  • Capacitor discharge

• What is the function of the impulse coupling?

  • To delay the spark and cause a rapid speed to make a hot spark

• What kind of gauge should be used to measure electrode gap in spark plugs?

  • Round wire gauge

• What are the two types of ignition systems used in turbine engines?

  • High voltage and Low voltage

• With which type of ignition system is a glow plug igniter used?

  • Low voltage

• How is the strength of a magnet in a magneto checked?

  • Points are held open, magneto is spun at specific speed and current of primary circuit measured

• In what position is the magnet in a magneto when the greatest change in flux density in the coil core takes place?

  • Few degrees past neutral when magnet is in the E-gap position

• What turns on the autoignition system in a turboprop engine?

  • Torque pressure switch when no torque is being produced

LUBRICATION SYSTEMS

A recip engine is found to have excessive oil consumption without evidence of any oil leaks. What is the likely cause?

Piston rings are worn or broken

What are the functions of a lubricating oil in recip engines?

Reduce friction and remove heat

Name the two important characteristics of aircraft engine oil?

Must be light enough to flow through passages and heavy enough to create an oil film

What could happen to an oil that is too low in viscosity at normal engine operating temperatures?

Premature wear from oil being too thin

What are some of the factors that must be considered by an engine manufacturer in determining the proper grade of oil for a particular engine?

Speed of the engine and operating loads

Why do aircraft recip engines use a relatively high viscosity oil?

Because the relatively large clearances and high temperatures

Name some oil contaminants.

Water, dirt, carbon, acids, metal particles

What is the possible indication of low oil pressure together with high oil temperature?

Low or inadequate supply of oil

In ashless dispersant oils, what function does the dispersant perform?

To prevent sludge formation by causing the sludge forming materials to repel each other

Why do oil reservoirs have expansion space?

For heat expansion and foaming

What could cause oil foaming?

Diluted/contaminated oil, oil level too high

What controls oil pressure in a gear type oil pressure pump?

Pressure relief valve

What function does an oil cooler bypass valve perform?

Allows oil to continue flowing if the oil cooler becomes blocked

What could be a possible indication if the oil cooler passage becomes obstructed?

Higher oil temperature

Where is the oil temperature bulb usually located?

At the engine oil inlet

What does the presence of metal particles in an engine oil filter indicate?

Depending on size and amount, excessive wear

What should be done if metal particles are found in an engine oil filter?

Follow manufacturer’s instructions

Where is the most critical point of lubrication in a gas turbine engine?

Turbine bearings

What type of oil is used in a turbine engine oil system?

Synthetic oil

Where are oil screens or filters most likely to be located in a turbine oil system?

Oil pressure system, scavenge system and last chance filters before oil nozzles

Name two types of turbine engine oil coolers.

Air cooled and fuel cooled

What is meant by viscosity?

Measure of resistance to flow

What is a wet sump lubrication system?

Where oil is stored inside the engine

What is a dry sump lubrication system?

Where oil is stored externally to the engine in a tank

How is oil temperature controlled in a recip engine?

Valve controlling amount of oil thru or around oil cooler

Is oil temperature showing on the instrument the temperature entering engine or leaving the engine?

Entering the engine

What is the purpose of the oil dilution valve on a recip engine?

To thin out the oil with gasoline in cold temps. When heated gas evaporates out

What is the function of a hopper in oil tanks used on some recip engines?

To help heat the oil quicker

What happens to gasoline that is used to dilute oil in crankcase of recip engine?

When the engine is heated it evaporates out

What is the purpose of sludge plugs in crankshaft of recip engines?

To keep sludge inside the crankshaft until overhaul

What pump has a larger capacity, the pressure pump or scavenger pump?

Scavenger

Why do full-flow oil filters have a spring-operated bypass valve in them?

So that if filter becomes clogged oil can flow thru system

What is the function of a fuel-oil heat exchanger in the lubrication system of a turbojet engine?

To heat the fuel and prevent icing in fuel filters

Where are last chance filters located in a turbojet engine?

Filter before oil nozzles to catch particulates that made it past other filters

Where is the oil tank in a dry sump recip engine vented?

To the engine crankcase

What is meant by spectrometric oil analysis?

Where the oil sample is burned and light waves measured to determine condition and contaminants

What indication would a pilot have with a low oil supply?

High oil temp and low pressure

What is meant by hot tank lubrication?

Where oil system has oil cooler in pressure side. Scavenger system pumps hot oil into the tank

What is meant be cold tank lubrication?

Where oil cooler is in the scavenger sid e. Oil into the tank has been cooled

COOLING SYSTEMS

What effect does excessive heat have on recip engines?

Shortened life of parts, changes combustion behavior and impairs lubrication

What is the purpose of cooling fins?

Increase surface area for increased cooling

What are the reasons for using engine cowlings, baffles and cowl air seals?

To direct air in close contact with cooling fins to cool engine

What is the purpose of cowl flaps and how are they operated?

To control amount of airflow through cowl for cooling, mechanically, electronically or hydraulically

How does an augmenter cooling system work?

Outer tube placed over exhaust creates venturi effect pulling more air through engine cowling

Where should cowl flaps be positioned for ground operations?

Open

What type of power is used to operate cowl flaps?

Mechanical, electronic, hydraulically

What should be done when cooling fin damage is discovered?

Depending on damage, may be repaired or cylinder replaced

Why is cowl flap adjustment important?

Because it controls amount of cooling, must be kept within tolerance to maintain proper cooling

How are turbine engines cooled?

By approximately 75% of the air passing through the engine

In a turbine engine, where does bleed air come from that is used to cool bearings and other parts?

The compressor section

What is the relationship between turbine engine upper temperature limits and power produced?

Higher temperatures that the engine can withstand will allow for higher power to be produced

What is the approximate percentage of air passing through a turbine engine that is used for cooling rather than combustion?

75%

What can be done to effectively allow higher gas temperatures in the turbine section of some engines?

Routing bleed air thru compressor rotors and stators to create cushion layer and keep temps low enough to prevent damage

What is pressure cooling of recip engines?

Air is forced thru the cooling fins because of a pressure differential

Which side of the air-cooled engine cylinder has the greatest amount of cooling fins?

Exhaust side

What is used in a helicopter to increase the amount of cooling air that flows over the cylinders?

Belt driven fan

How is the structure around a turbine engine usually protected from excessive heat?

By insulation blankets

What is the function of blast tubes that are installed in a pressure cooling system of a recip engine?

To direct cooling air onto accessories

What material is the insulation blanket used to protect aircraft structures made of?

Fiberglass and metal foil sheets

ENGINE FIRE PROTECTION SYSTEMS

What types of fire detector systems are used for engine fire detection?

Overheat, rate of rise and flame detectors

How does a thermal switch fire protection system operate?

When heated to a predetermined heat they expand and close points alerting crew in cockpit

How many thermal switches are needed in a thermal switch fire protection system?

At least one

What kind of fire detection system allows more complete coverage that a spot type system?

Continuous loop type

What happens if an engine equipped with a thermocouple fire warning system overheats slowly?

No indication

What electrical power is required for a thermocouple fire protection system to operate?

Only power required for the warning light

What is the likely cause of a false fire warning?

Fire sensing loop bent or kinked

What are the fire extinguishing systems designed to do?

Dilute oxygen levels or reduce temperature so that combustion cannot occur

Describe how the Kidde and Fenwal continuous loop fire protection systems function.

Use a grounded outer shell, a thermal resistor material and an internal wire. When it heats the resistance lowers allowing the positive center wire to connect to the outer shell.

The Kidde system is similar but uses two wires, one grounded and one positive in a thermal resistor material. Same operation

What elements must be present for a fire to occur?

Oxygen, heat and a fuel source (something to burn)

What group of fire extinguishing agents are no longer manufactured because of environmental concerns?

Halogenated hydrocarbons

How are the fire extinguishing agents distributed?

Through perforated tubing or discharge nozzles

What is the purpose of the discharge cartridge and how is it activated?

The cartridge fires a projectile that hits a frangible disk that breaks, releasing the agent

How is a fire extinguisher system with a high-rate discharge classified?

As an HRD fire extinguishing system

What do red and yellow discs in a fire extinguishing system indicate?

Red indicates thermal discharge. Yellow indicates normal discharge

How is the fire extinguishing agent in HRD system distributed, and how long does it take to discharge?

Thru series of high-pressure tubes. Takes one to two seconds to discharge

What is the purpose of a pressure gauge in a fire extinguishing system?

To indicate pressure in container and display if there are leaks

Can a thermal switch fire detection system indicate a general overheat?

No, it only trips at a predetermined temperature above overheat temperatures

Can a thermocouple type fire detection system indicate a general overheat?

No, Thermocouples rely on a rate of rise to indicate fires

How is a thermocouple type indication system checked for operation?

By heating a test thermocouple in the system

Does a break in a continuous loop system keep the system from detecting a fire?

No, a fault will show up to the break

Does a pressure type continuous element fire detector indicate a general overheat and a fire?

Yes, high temp on small portion or low temp on large area can trigger the pneumatic switch

What are the two most commonly used fire extinguishing agents used in engine fires?

Carbon dioxide and Halon 1301

What extinguishing agent is commonly used in turbine engines?

Halon 1301

What happens when a pilot pulls the T-handle in the cockpit of a jet transport aircraft?

It cuts off fuel, oil, bleed air, electrical to the engine, primes extinguishing system

How can a mechanic determine the state of charge of the HRD bottles of fire extinguishing agent?

By the pressure gauge or by weighing

What type of fire detection system operates on rate of temperature rise?

Thermocouple system

How is a pressure type continuous element fire detection system tested for operation?

low voltage current is sent through system to heat it up and release gases to close switch

PROPELLERS

What is the function of a propeller?

Propeller creates thrust to pull or push plane thru air

What is the difference between a fixed pitch and controllable pitch propeller?

Fixed pitch has single preset angle that cannot be changed, controllable pitch can be changed by pilot for flight conditions

How are some wooden propeller blades protected from wear and damage?

By metal tipping on the leading edge and tip

What happens to the blade angle of a constant speed propeller during a constant power dive?

It will increase to prevent an overspeed

What are the functions of a constant speed propeller governor?

Boosts oil pressure and controls oil going to propeller to control pitch and speed

What is the purpose of propeller counterweight?

To move the blade angle to a higher pitch using centrifugal force

What is meant when a propeller governor is in an “on-speed” condition?

When the speeder spring and flyweights are in equilibrium

How is a constant speed feathering propeller feathered?

By porting oil from the hub allowing the spring and counterweights to move it to feathered position

What is an unfeathering accumulator?

An oil accumulator used to provide oil pressure for unfeathering

What is the “Alpha range” and “Beta range” and where are they found?

Ranges found on turboprop engines. Alpha creates forward thrust while beta produces no thrust and reverse thrust

What systems are commonly used for propeller ice control?

Electric de-ice boots and alcohol anti-icing

What propeller repairs can be done by a certified mechanic with a powerplant rating?

Minor repairs and minor alterations, major work must be done my manufacturer or propeller repair station

How are wooden propellers generally cleaned?

With use of brush or cloth and soapy water

What type of non-destructive testing should be accomplished to a propeller after blending?

Refer to manufacturer’s manual for correct procedure

What are the two criteria used by many manufacturers to determine the amount of bend damage that can be repaired by cold bending of aluminum propellers?

The extent of the bend and its blade station location

How can repair file marks be removed from an aluminum propeller?

Very fine sandpaper

When performing static balance on a two bladed propeller, what positions must the propeller be placed in when measurements are taken?

Vertical and horizontal

What is a propeller protractor used for?

Used to measure blade angle

What blade conditions can cause engine vibration?

Imbalance, out of track, incorrect blade angle

What is blade tracking?

Procedure of checking tip location relative to each other

What controls both manifold pressure and RPM on an engine equipped with a fixed pitch propeller?

Throttle

Should an adjustable pitch prop be in high pitch or low pitch for takeoff?

Low pitch

What is done to cause a Hyrdomatic propeller to feather?

Oil is pumped into the hub

What is done to cause a McCauley propeller to feather?

Oil is drained from the hub

Does centrifugal twisting force increase or decrease the pitch?

Decrease pitch

Do counterweights increase or decrease propeller pitch?

Increase pitch

What can be done to prevent the front cone from bottoming on a splined shaft?

Move the rear cone forward with a spacer

What is the purpose of small holes on the tips of wooden propellers?

To allow water to drain from the propeller

What is the function of a snap ring inside the hub of a propeller that is mounted on a tapered or splined shaft?

To allow for removal after nut is loosened

What is adjusted inside the governor for a constant speed propeller to change the speed at which the propeller is operating?

The tension on the speeder spring

Is the flat surface of a propeller the blade face or the blade back?

Blade face

What keeps a McCauley feathering propeller from feathering when the engine is shutdown on the ground?

Spring loaded mechanism and pins

POWERPLANT AND PROPELLER AIRWORTHINESS INSPECTIONS

What publications can be used as a guide for 100-hour inspections on aircraft engines?

Manufacturer’s instructions and FAR 43 appendix D

How do you identify the engine serial number?

Look on the data plate

Prior to returning a recip engine to service after a 100-hour inspection, what operation checks must be performed?

Power output, check magnetos, fuel and oil pressure, cylinder and oil temperature

Where are life-limited parts of an engine listed?

In the maintenance manuals, TCDS, airworthiness limits of instruction for continued airworthiness

Where can engine operating limits be found?

TCDS, engine maintenance manual, pilots operating handbook

Why are hot section inspections performed on turbine engines?

To ensure part integrity and wear of hot section

What inspections must be performed following a turbine engine overspeed?

Refer to manufacturer maintenance manual

What inspections must be performed on a turbine engine if the exhaust gas temperature exceeds limitations?

Hot section inspection

What FAA approvals are required when installing an engine that is not on the aircraft type certificate?

An STC or FAA field approval

Under what conditions is compliance with an engine service bulletin mandatory?

When part of an AD, or when compliance is required by approved specifications for commercial or air carrier operations. If overhaul procedure requires compliance

What determines whether or not a 100-hour inspection is required for an aircraft?

Whether is operates for hire

Who is authorized to perform an annual powerplant inspection?

AP W/ IA

What are the two types of compression checks that can be performed on a recip engine?

Direct and differential

What items are checked in a hot section inspection of a turbine engine?

Combustion section, turbines and exhaust for cracks, warping, hot spots. burns

What is the most common type of damage found in a hot section of a turbine engine?

Cracks

Is the use of a checklist required for a 100-hour or annual inspection?

Yes

What inspection must be performed on an aircraft recip engine if it has been operating with turbine fuel?

Inside the cylinder, drain oil and check filters, runup with AVGAS to verify correct operation

POWERPLANT TROUBLESHOOTING

What are the possible causes for a turbojet or turbofan engine having high exhaust gas temperatures, low RPM and high fuel flow at all engine pressure ratios?

Turbine damage or loss of efficiency from wear

AUXILARY POWER UNITS

Where are most APUs located in modern jet transport aircraft?

In the tail section

What is the function of an APU?

To provide electric power and compressed air when main engines aren’t operating

What are the two sources of compressed air from an APU?

Bleed air from the compressor or a load compressor from the free turbine

Where in maintenance information based on ATA code would you find instructions for inspecting and servicing engine on airborne APU?

49 20

How is most troubleshooting done for a modern APU?

By fault codes generated by the FADEC