NCAA Aircraft Maintenance Engineer Licence - Powerplant (Nigeria)

What is the correct sequence of strokes in a four-stroke cycle reciprocating aircraft engine?

• AIntake, Power, Compression, Exhaust
• BIntake, Compression, Power, Exhaust
• CCompression, Intake, Power, Exhaust
• DPower, Intake, Compression, Exhaust

What is the primary function of oil control rings on an aircraft engine piston?

• ATo prevent cylinder gas leakage into the crankcase
• BTo regulate the thickness of the oil film on the cylinder wall and scavenge excess oil
• CTo support the wrist pin within the piston bosses
• DTo transfer heat directly from the piston head to the crankshaft

Why is valve overlap incorporated into four-stroke engine timing schedules?

• ATo prevent spark plug fouling at low idle speeds
• BTo allow better cylinder scavenging and intake charge induction using gas inertia
• CTo increase the compression ratio during high-altitude operation
• DTo ensure complete closure of both valves during the power stroke

What is the main cause of detonation in a reciprocating engine?

• AInstantaneous uncontrolled explosion of the unburned fuel-air mixture ahead of the flame…
• BPre-ignition caused by glowing carbon deposits before spark plug firing
• CExcessively rich fuel mixture at high power settings
• DUsing an aviation fuel with an octane rating higher than specified

Which component connects the piston to the crankshaft in a reciprocating aircraft engine?

• APush rod
• BConnecting rod
• CRocker arm
• DCamshaft follower

Which thermodynamic cycle governs the operation of gas turbine engines?

• AOtto cycle
• BDiesel cycle
• CBrayton cycle
• DCarnot cycle

What is the primary function of the compressor diffuser section in a gas turbine engine?

• ATo decrease air pressure and increase air velocity before entering the combustor
• BTo convert high-velocity airflow from the compressor into high static pressure
• CTo mix fuel and air thoroughly prior to ignition
• DTo direct exhaust gas flow toward the turbine nozzle guide vanes

What is the purpose of secondary air entering the liner of a gas turbine combustion chamber?

• ATo participate directly in primary flame combustion
• BTo cool the liner walls and dilute hot gases to acceptable turbine entry temperatures
• CTo increase fuel atomization pressure at low engine RPM
• DTo prevent compressor surge during sudden acceleration

What is the function of turbine nozzle guide vanes (NGVs)?

• ATo slow down gas velocity and decrease pressure
• BTo direct hot expanding gases onto turbine blades at the optimum angle and accelerate the…
• CTo drive the accessory gearbox via bevel gears
• DTo compress air before entering the combustion chamber

What is the main purpose of the exhaust cone assembly on a turbojet engine?

• ATo accelerate exhaust gas velocity above Mach 2
• BTo collect exhaust gases from the turbine and transform turbulent swirl into a smooth axi…
• CTo ignite unburned fuel remnants for extra thrust
• DTo cool exhaust gas before exit

Which engine section is classified as part of the 'cold section' in a gas turbine engine?

• ACombustion chamber
• BTurbine nozzle guide vanes
• CCompressor section
• DExhaust tailcone

What is turbine blade 'creep'?

• ARapid elastic deformation of blades during engine startup
• BSlow, permanent elongation of turbine blades due to prolonged exposure to high centrifuga…
• CVibrational cracking of compressor blades caused by bird ingestion
• DOxidative erosion of blade tip coatings

What is the stoichiometric air-fuel ratio by weight for complete combustion of standard aviation gasoline (Avgas)?

• A8:1
• B12:1
• C15:1
• D20:1

Why must the mixture setting of a float-type carburetor be leaned as aircraft altitude increases?

• AAir density decreases while fuel density remains constant, causing an overly rich mixture
• BAir density increases, requiring higher fuel pressure to maintain power
• CFuel evaporates faster at high altitude due to low ambient temperature
• DCarburetor ice formation accelerates at high altitude unless leaned

What is the primary function of an accelerating system in an aircraft carburetor?

• ATo lean the mixture during rapid engine deceleration
• BTo supply momentarily enriched fuel when the throttle is opened rapidly
• CTo shut off fuel flow completely when the mixture control is moved to IDLE CUTOFF
• DTo maintain constant float bowl fuel level during aerobatic maneuvers

What does the acronym FADEC stand for in modern aircraft engine management?

• AFull Authority Digital Engine Control
• BFlight Automated Direct Engine Calibration
• CFuel And Diagnostics Electronic Controller
• DFrequency Adjusted Digital Engine Computer

What is a main advantage of a duplex fuel nozzle over a simplex fuel nozzle in gas turbine combustors?

• AIt requires no high-pressure fuel pump
• BIt provides superior atomization and spray pattern across both low-flow starting and high…
• CIt eliminates the need for secondary combustion air
• DIt operates exclusively on avgas without carbon buildup

Why are aircraft reciprocating engines equipped with a dual ignition system (two magnetos and two spark plugs per cylinder)?

• ATo double the engine operating speed
• BTo provide safety redundancy and improve combustion efficiency through faster flame propa…
• CTo eliminate the need for grounding P-leads
• DTo power cockpit electronic instruments directly

In a high-tension magneto ignition system, when do the breaker points open?

• AWhen the primary current is zero
• BWhen the magnetic rotor is in the E-gap position, inducing maximum primary voltage collap…
• CDuring the intake stroke of the cylinder
• DWhen the ignition switch is turned to OFF

When are igniter plugs typically energized in a gas turbine engine?

• AContinuously throughout the entire flight from takeoff to landing
• BDuring engine start cycles, anti-ice operation, takeoff, and severe weather conditions
• COnly during ground maintenance testing
• DWhen the main fuel shutoff valve is closed

What is the primary characteristic of a dry-sump engine lubrication system?

• AOil is stored inside the engine crankcase sump
• BOil is stored in a separate external supply tank and scavenged from the crankcase by a pu…
• CIt uses no oil pump and relies on splash lubrication
• DIt uses water mixed with oil to reduce viscosity

What is the function of the oil pressure relief valve in an engine lubrication system?

• ATo bypass dirty oil around the oil filter when clogged
• BTo maintain system oil pressure within specified limits by bypassing excess oil back to t…
• CTo prevent oil from flowing into cylinders during engine shutdown
• DTo control oil temperature entering the oil cooler

How does a thermostatic bypass valve in an oil cooler system respond when engine oil is cold?

• AIt routes cold oil through the cooler core matrix for rapid cooling
• BIt allows cold oil to bypass the cooler core directly to the engine, speeding up warm-up
• CIt shuts down the engine oil pressure pump automatically
• DIt increases scavenge pump speed

What is the difference between geometric pitch and effective pitch of an aircraft propeller?

• AGeometric pitch is less than effective pitch due to mechanical friction
• BGeometric pitch is the theoretical distance advanced per revolution without slip; effecti…
• CGeometric pitch applies to wooden propellers only; effective pitch applies to metal prope…
• DGeometric pitch is measured at the blade root; effective pitch is measured at the tip

What component in a constant-speed propeller governor senses engine RPM changes?

• ASpeeder spring
• BFlyweight assembly
• CPilot valve spool
• DBoost pump piston

Why is a propeller feathered on a twin-engine aircraft following an in-flight engine failure?

• ATo keep the inoperative engine windmilling at high RPM
• BTo rotate blade leading edges parallel to airflow, minimizing aerodynamic drag and asymme…
• CTo lock the propeller blades in reverse pitch to act as an air brake
• DTo increase oil pressure inside the failed engine crankcase

What defines the 'Beta range' of a turbopropeller system?

• AThe high-speed cruise pitch angle regime governed by flyweights
• BThe ground operating mode where blade pitch is directly controlled by the power/thrust le…
• CThe automatic feathering angle range above 85 degrees
• DThe emergency pitch position during governor oil failure

What indication on an Exhaust Gas Temperature (EGT) indicator signifies peak fuel economy during mixture leaning?

• AEGT reaches its lowest reading
• BEGT rises to a peak and then drops as mixture is leaned further past peak
• CEGT fluctuates violently between 500°C and 1000°C
• DEGT drops to zero immediately

Engine Pressure Ratio (EPR) is the ratio of which two pressures in a gas turbine engine?

• ACompressor inlet total pressure to turbine outlet total pressure
• BTurbine discharge total pressure to compressor inlet total pressure
• CFuel pump outlet pressure to combustor pressure
• DAmbient static pressure to burner pressure

Under Nig. CARs Part 2, what privilege is granted to the holder of an AME licence endorsed with a Powerplant rating?

• ATo pilot multi-engine turboprop aircraft in commercial air transport
• BTo certify maintenance, overhaul, and release to service aircraft powerplants and associa…
• CTo conduct air traffic control duties for twin-engine aircraft
• DTo issue airworthiness certificates for newly manufactured aircraft

An engine cylinder has a piston displacement volume ($V_d$) of 90 cubic inches and a clearance volume ($V_c$) of 15 cubic inches. What is the compression ratio of this cylinder?

• A6:1
• B7:1
• C8:1
• D9:1

Why must cold valve clearances on solid (rigid) lifter aircraft engines be set precisely according to manufacturer specifications?

• ATo compensate for thermal expansion of cylinder components during engine operation
• BTo increase fuel pressure to the main jet during warm-up
• CTo lock the camshaft lobes in position at high RPM
• DTo prevent oil from leaking past valve guides into the exhaust port

What is the main physical difference between engine pre-ignition and detonation?

• APre-ignition occurs after spark plug firing; detonation occurs before
• BPre-ignition is caused by hot spots igniting the charge before spark ignition; detonation…
• CPre-ignition only happens in turbine engines; detonation happens in piston engines
• DPre-ignition increases cylinder head temperature while detonation drops head temperature

Why are cylinder barrels of some air-cooled aircraft engines ground with a slight 'choke' (tapered bore near the top)?

• ATo reduce piston skirt weight near the wrist pin
• BTo allow the top of the cylinder barrel to expand more when hot, producing a straight uni…
• CTo restrict exhaust gas flow exiting the combustion chamber
• DTo compress the piston rings permanently at high speed

Calculate the total piston displacement of a 6-cylinder engine with a cylinder bore of 5.0 inches and a stroke of 4.0 inches.

• A471.2 cubic inches
• B376.9 cubic inches
• C314.2 cubic inches
• D589.0 cubic inches

How do hydraulic valve lifters maintain zero valve clearance during engine operation?

• AThey rely on mechanical screw threads adjusted automatically by spring tension
• BThey use engine oil under pressure trapped in a sealed plunger chamber to automatically e…
• CThey compress secondary valve springs during engine warm-up
• DThey bleed all engine oil out of the pushrod when engine speed increases

What is the purpose of dynamic dampers fitted to aircraft engine crankshaft counterweights?

• ATo balance static weight differences between pistons
• BTo absorb and damp torsional vibrations created by power impulses
• CTo drive the oil pump gears directly
• DTo reduce aerodynamic drag inside the crankcase

According to Nig. CARs Part 5 airworthiness maintenance standards, what distinguishes a major engine overhaul from a top overhaul?

• AMajor overhaul requires replacing all fuel lines; top overhaul replaces ignition harness
• BMajor overhaul involves complete disassembly, inspection, repair, and testing of the cran…
• CMajor overhaul can be certified by any A&P mechanic; top overhaul requires an NCAA inspec…
• DTop overhaul requires complete replacement of the crankshaft

During a differential cylinder compression test on a piston engine using an 80 psi supply pressure, a reading of 45/80 is recorded with air escaping audibly from the crankcase breather. What does this indicate?

• ALeaking intake valve
• BLeaking exhaust valve
• CWorn or defective piston rings / cylinder barrel
• DCracked cylinder head intake port

Calculate the Indicated Horsepower (IHP) of a 4-cylinder, four-stroke engine operating under the following parameters: Mean Effective Pressure (P) = 130 psi, Stroke Length (L) = 0.375 ft (4.5 in), Piston Area (A) = 19.6 sq in, RPM = 2400 (N = 1200 power strokes/min per cylinder).

• A138.8 HP
• B277.6 HP
• C69.4 HP
• D555.2 HP

What aerodynamic condition causes an axial-flow compressor stall in a gas turbine engine?

• AExcessive air velocity entering the compressor relative to rotor speed
• BHigh angle of attack of compressor rotor blades exceeding critical stall angle
• CExcessive turbine exhaust pressure pushing air backward through combustor
• DFuel flow dropping below minimum idle threshold

How do Variable Inlet Guide Vanes (VIGVs) and transient bleed valves work together to prevent compressor stall during engine acceleration?

• AVIGVs open wide and bleed valves close at low RPM
• BVIGVs adjust airflow angle into front stages while bleed valves unload excess air pressur…
• CVIGVs inject fuel while bleed valves inject secondary cooling air
• DVIGVs increase turbine speed directly via mechanical gearing

What is a design feature of a can-annular combustion chamber system?

• AIt uses a single continuous outer casing enclosing individual flame cans connected by fla…
• BIt consists of a single donut-shaped liner with no individual cans
• CIt uses separate independent combustion cans each having its own outer housing and exhaus…
• DIt relies entirely on reverse-flow radial tubes without interconnectors

What is the principle of Active Clearance Control (ACC) in gas turbine engine turbine cases?

• AAdjusting fuel flow based on turbine blade vibration frequency
• BBlowing cool fan air onto the turbine casing to thermally shrink the case, minimizing bla…
• CHydraulically moving turbine shaft bearings forward during high power
• DMechanically grinding turbine blade tips in flight

Why are gas turbine rotor blades often designed with an impulse profile at the root and a reaction profile at the tip (impulse-reaction blades)?

• ATo make the manufacturing process simpler and cheaper
• BTo equalize gas workload and pressure distribution along the entire length of the blade
• CTo prevent hot exhaust gas from entering the turbine disk
• DTo eliminate centrifugal force at the blade tip

In a convergent-divergent (C-D) exhaust nozzle operating at supersonic pressure ratios, what happens to exhaust gas flow in the divergent section?

• AGas velocity decreases and static pressure increases
• BGas velocity increases to supersonic speed while static pressure drops
• CGas temperature increases while velocity remains subsonic
• DGas density increases rapidly while velocity drops to zero

If a high-bypass turbofan engine ingests 100 kg/s of total air, with 80 kg/s passing through the bypass duct and 20 kg/s passing through the core, what is the bypass ratio?

• A0.25:1
• B4:1
• C5:1
• D80:1

What safety interlock requirement must be met before a thrust reverser system can deploy in flight or on ground?

• AEngine oil temperature must exceed 100°C
• BWeight-on-wheels (squat switch) signal or radio altimeter low-altitude interlock must con…
• CFADEC dual channels must be manually turned off
• DPropeller governor flyweights must be locked