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Engineer Aircraft practice questions

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Question 1Aircraft Structures and Airframe Systems

In aircraft structural repair documentation, what does the term 'gauge' most commonly refer to when applied to sheet metal parts?

  1. The gap tolerance between mating skins
  2. The thickness of the sheet expressed on a standardized numbering scale Correct answer.
  3. The torque value applied to a fastener
  4. The spanwise curvature of a formed rib

Explanation

Gauge is a standardized numbering convention for sheet thickness; lower gauge numbers denote thicker material. It is a dimensional descriptor for sheet stock, not a measure of curvature, fastener torque, or joint gap.

Question 2Aircraft Structures and Airframe Systems

Which structural member of a semi-monocoque wing carries the bending loads along the span?

  1. The trailing edge wedge
  2. The spar caps Correct answer.
  3. The access panel frames
  4. The leading edge skin

Explanation

Spar caps (booms) are the longitudinal members at the top and bottom of the spar that resist spanwise bending by carrying tension and compression. Skin contributes shear and some bending, but the caps are the primary bending elements.

Question 3Aircraft Structures and Airframe Systems

A riveted lap joint in a pressurized fuselage skin is being evaluated. Which stress condition most directly drives the fatigue life of the joint?

  1. Static shear in the frame attachments
  2. Secondary bending at the faying surface plus cyclic hoop stress Correct answer.
  3. Compressive buckling of the stringer web
  4. Bearing stress on the rivet shank only

Explanation

In a lap joint the load path eccentricity causes secondary bending at the faying surface, which combines with the cyclic hoop stress from pressurization. This local bending amplification is what makes lap joints fatigue-critical.

Question 4Aircraft Structures and Airframe Systems

What is the primary function of a stringer in a semi-monocoque fuselage?

  1. To carry the pressurization hoop load alone
  2. To seal the fuel tank boundary
  3. To stiffen the skin against buckling and carry longitudinal loads Correct answer.
  4. To provide the main attachment for the landing gear beam

Explanation

Stringers run longitudinally and stiffen the skin so it can carry shear and compression without buckling prematurely, while also reacting axial loads. Hoop load is carried primarily by the skin and frames, not by stringers alone.

Question 5Aircraft Structures and Airframe Systems

A control surface is found to have excessive free play at its hinge. Which consequence is most directly associated with this condition?

  1. Reduced cabin pressurization leakage
  2. Increased flutter susceptibility and degraded control response Correct answer.
  3. Accelerated tire wear on landing
  4. Higher fuel consumption at cruise

Explanation

Free play at a hinge allows the surface to move relative to the commanded position and can couple with structural modes, raising flutter risk and degrading control precision. It is a control-surface integrity issue, not a propulsion or cabin issue.

Question 6Aircraft Structures and Airframe Systems

During a structural repair, a doubler is to be installed over a cracked skin panel. What is the primary purpose of the doubler?

  1. To increase the aerodynamic smoothness of the skin
  2. To serve as a jacking point for maintenance
  3. To provide a grounding point for static discharge
  4. To restore the load path and reduce stress at the crack tip Correct answer.

Explanation

A doubler adds material and fasteners so that load bypasses the damaged region, lowering stress intensity at the crack tip. It is a structural restoration measure, not an aerodynamic or electrical feature.

Question 7Aircraft Structures and Airframe Systems

Which inspection method is best suited to detecting subsurface delamination in a composite wing skin?

  1. Ultrasonic inspection Correct answer.
  2. Dye penetrant inspection
  3. Visual inspection with a magnifier
  4. Magnetic particle inspection

Explanation

Ultrasonic inspection transmits sound into the laminate and detects reflections from internal interfaces such as delaminations. Dye penetrant and magnetic particle methods are surface techniques, and visual inspection cannot see internal flaws.

Question 8Aircraft Structures and Airframe Systems

What is the purpose of a lightning protection mesh embedded in a composite wing skin?

  1. To carry primary bending loads
  2. To provide a path for fuel tank venting
  3. To conduct lightning current and protect the underlying structure Correct answer.
  4. To act as a strain sensor for health monitoring

Explanation

Composite structures conduct poorly, so a metallic mesh or foil provides a conductive path that dissipates lightning current and limits damage. It is an electrical protection feature, not a primary load path.

Question 9Aircraft Structures and Airframe Systems

A fuselage frame is designed with a flanged cross-section rather than a flat bar. What is the primary structural benefit?

  1. Improved aerodynamic contour of the fuselage
  2. Elimination of the need for stringers
  3. Reduced need for fasteners to the skin
  4. Increased resistance to local buckling and more efficient load distribution Correct answer.

Explanation

Flanges increase the section's moment of inertia and stiffen the web against local buckling, allowing the frame to carry hoop and concentrated loads efficiently. Fastener requirements and stringer needs are unaffected.

Question 10Aircraft Structures and Airframe Systems

In a fail-safe structural design philosophy, what is the key design feature?

  1. The structure can carry limit load after failure of a primary element Correct answer.
  2. The structure has infinite fatigue life
  3. The structure relies on a single load path
  4. The structure uses only composite materials

Explanation

Fail-safe design ensures that after a discrete element fails, the remaining structure can carry limit load until the failure is detected. It does not imply infinite life, and it specifically avoids single load paths.

Question 11Aircraft Structures and Airframe Systems

During a structural inspection, a crack is found at a fastener hole in a wing spar cap. Which action is most consistent with damage-tolerant design practice?

  1. Assess crack size against allowable limits and apply a repair or monitoring plan Correct answer.
  2. Increase the aircraft's maximum takeoff weight to compensate
  3. Ignore the crack until it reaches the next scheduled inspection
  4. Immediately scrap the entire wing

Explanation

Damage-tolerant practice compares the detected crack size with established allowable limits and defines repair or inspection intervals accordingly. Simply ignoring the crack or scrapping the wing without assessment is not consistent with the philosophy.

Question 12Aircraft Structures and Airframe Systems

What is the role of a shear tie in a built-up wing box?

  1. To provide a fuel drain path
  2. To carry the entire bending moment of the wing
  3. To transfer shear between the skin and the spar web Correct answer.
  4. To mount the wing tip navigation light

Explanation

Shear ties connect skin panels to spar webs and ribs, transferring shear loads across the joint. They do not carry the primary bending moment, which is the role of the spar caps.

Question 13Aircraft Structures and Airframe Systems

Which factor most directly determines the fatigue life of a riveted aluminum fuselage joint?

  1. The color of the protective primer
  2. The type of hydraulic fluid used
  3. The stress concentration at the fastener holes and the load spectrum Correct answer.
  4. The number of cabin windows

Explanation

Fatigue life depends on local stress concentrations at holes and the cyclic load spectrum the structure experiences. Paint color, window count, and hydraulic fluid are unrelated to structural fatigue.

Question 14Aircraft Structures and Airframe Systems

A composite skin panel is being repaired with a bonded patch. Which surface preparation step is most critical to bond integrity?

  1. Heating the patch above the cure temperature
  2. Increasing the fastener count around the patch
  3. Removing contaminants and creating the specified surface roughness Correct answer.
  4. Applying a coat of paint before bonding

Explanation

Bonded repairs depend on a clean, properly abraded surface to achieve adhesion; contamination or inadequate roughness leads to weak bonds. Paint before bonding and overheating the patch would both degrade the joint.

Question 15Aircraft Structures and Airframe Systems

What is the primary function of a wing rib?

  1. To carry the entire wing bending moment
  2. To maintain the airfoil shape and transfer loads between skin and spar Correct answer.
  3. To house the wingtip anti-collision light
  4. To provide the main fuel storage volume

Explanation

Ribs maintain the airfoil contour and distribute loads between the skin and the spars. Bending moment is carried by the spar caps, and fuel storage is a separate tank design function.

Question 16Aircraft Structures and Airframe Systems

Aircraft skin panels are often chem-milled to produce pockets of reduced thickness. What is the primary purpose of this process?

  1. To improve the paint adhesion
  2. To increase the skin's electrical conductivity
  3. To reduce weight while retaining local stiffness where needed Correct answer.
  4. To eliminate the need for stringers

Explanation

Chem-milling removes material from low-stress areas to save weight while leaving thicker sections where loads require them. It does not affect conductivity or paint adhesion, and stringers are still needed.

Question 17Aircraft Structures and Airframe Systems

Which structural element primarily reacts the pressurization hoop stress in a cylindrical fuselage?

  1. The floor beams
  2. The longitudinal stringers
  3. The cargo door hinges
  4. The circumferential skin and frames Correct answer.

Explanation

Hoop stress from internal pressure acts circumferentially and is carried by the skin, with frames providing stability and load distribution. Stringers run longitudinally and react axial loads instead.

Question 18Aircraft Structures and Airframe Systems

What is the purpose of a bonded doubler in a composite repair?

  1. To increase the aircraft's maximum cruise speed
  2. To provide a mounting point for the landing gear
  3. To act as a lightning protection mesh
  4. To restore load path and reduce stress at the damaged area Correct answer.

Explanation

A bonded doubler restores the load path across a damaged region and reduces stress at the damage boundary. It is a structural repair, not a performance or system feature.

Question 19Aircraft Structures and Airframe Systems

In a damage-tolerant design, what does the term 'inspection threshold' refer to?

  1. The torque value for the inspection panel fasteners
  2. The minimum thickness of paint allowed on the structure
  3. The maximum altitude at which inspections are performed
  4. The number of flight cycles before the first inspection for a given crack size Correct answer.

Explanation

The inspection threshold is the flight cycle count at which the first inspection for a specific damage scenario must be performed, based on crack growth analysis. It is a damage-tolerance scheduling parameter, not an altitude or paint specification.

Question 20Aircraft Structures and Airframe Systems

A wing spar cap is found to have a small crack. Which repair approach is generally preferred for a primary structural element?

  1. Ignoring the crack if it is below 1 mm
  2. Increasing the aircraft's operating speed to reduce load
  3. Replacing or reinforcing the affected section per approved data Correct answer.
  4. Applying a temporary tape patch

Explanation

Primary structural elements require repair or reinforcement in accordance with approved engineering data to restore load capability. Tape patches, speed increases, and arbitrary size thresholds are not acceptable.

Question 21Aircraft Structures and Airframe Systems

Which of the following best describes the function of a wing-to-fuselage attachment fitting?

  1. To transfer wing loads into the fuselage structure Correct answer.
  2. To support the passenger cabin floor
  3. To provide aerodynamic sealing of the wing root
  4. To house the wing fuel vent

Explanation

Wing attachment fittings are the structural interface that transfers shear, bending, and torsion loads from the wing into the fuselage. They are not sealing, venting, or floor support elements.

Question 22Aircraft Structures and Airframe Systems

A composite laminate is designed with plies oriented at 0, 90, and ±45 degrees. What is the primary reason for including ±45 degree plies?

  1. To simplify the manufacturing process
  2. To improve shear and torsional load capability Correct answer.
  3. To increase the laminate's thermal expansion
  4. To reduce the laminate's electrical resistance

Explanation

±45 degree plies provide shear and torsional stiffness and strength, complementing the axial and transverse plies. They are not included for electrical, thermal, or manufacturing reasons.

Question 23Aircraft Structures and Airframe Systems

What is the purpose of a corrosion-inhibiting compound applied in a lap joint?

  1. To act as a primer for the topcoat
  2. To increase the joint's electrical conductivity
  3. To provide structural load transfer between the skins
  4. To reduce friction between the mating surfaces and prevent moisture ingress Correct answer.

Explanation

Corrosion-inhibiting compounds seal the faying surfaces and displace moisture, reducing the risk of corrosion in the joint. They do not carry structural load or serve as a primer.

Question 24Aircraft Structures and Airframe Systems

Which statement best describes the function of a fuselage bulkhead?

  1. It houses the main landing gear actuator
  2. It closes off a pressure boundary and carries concentrated loads Correct answer.
  3. It serves as the primary wing bending member
  4. It provides longitudinal skin stiffening along the entire fuselage

Explanation

A bulkhead is a transverse structural member that closes a pressure boundary, such as at the cockpit or aft pressure dome, and reacts concentrated loads. It is not a longitudinal stiffener or wing member.

Question 25Aircraft Structures and Airframe Systems

During a structural repair, a fastener hole is found to be oversized. Which action is most appropriate?

  1. Use an approved oversize fastener or repair scheme Correct answer.
  2. Fill the hole with epoxy and redrill at the same size
  3. Install the original fastener with extra sealant
  4. Leave the hole open and rely on adjacent fasteners

Explanation

Oversized holes require an approved oversize fastener or a defined repair scheme to restore joint capability. Using the original fastener with sealant or leaving the hole open would not restore the load path.

Question 26Aircraft Structures and Airframe Systems

In a semi-monocoque wing, which member carries the bending moment produced by lift while the skin primarily resists shear and torsion?

  1. The rib
  2. The stringer
  3. The spar cap Correct answer.
  4. The leading-edge skin

Explanation

In semi-monocoque construction the bending moment is reacted mainly as axial tension and compression in the spar caps, which are placed far from the neutral axis to maximise the second moment of area. The skin carries shear and torsion, ribs maintain aerofoil shape and stabilise the skin, and stringers support the skin against buckling.

Question 27Aircraft Structures and Airframe Systems

A pressurised fuselage skin develops a fatigue crack that grows slowly and is detected at scheduled inspections before it can reduce residual strength below limit load. Which design philosophy does this behaviour illustrate?

  1. Damage-tolerant design Correct answer.
  2. Safe-life design
  3. Fail-safe design
  4. Ultimate-strength design

Explanation

Damage tolerance accepts that cracks exist and demonstrates that they grow slowly enough to be found at defined inspection intervals before residual strength falls below the required level. Fail-safe relies on load paths or crack stoppers to arrest damage, while safe-life retires the part before any crack is expected to initiate.

Question 28Aircraft Structures and Airframe Systems

Which feature of a riveted fuselage lap joint most directly reduces the risk of fretting and exfoliation corrosion between the faying surfaces?

  1. Installing rivets with a larger head diameter
  2. Increasing the rivet pitch along the joint
  3. Applying a sealant or corrosion-inhibiting compound between the mated surfaces Correct answer.
  4. Reducing the number of rivet rows in the joint

Explanation

Fretting and exfoliation corrosion occur where moisture and relative movement exist between closely mated surfaces. A sealant or corrosion-inhibiting compound excludes moisture and lubricates the interface, which is why it is applied during joint assembly. Rivet pitch, head size, and row count affect load transfer and fatigue, not the chemistry of the faying surface.

Question 29Aircraft Structures and Airframe Systems

A control surface is mass-balanced about its hinge line. What is the primary purpose of this balancing?

  1. To reduce the hinge moment required from the actuator in steady flight
  2. To prevent flutter by keeping the centre of gravity close to or ahead of the hinge line Correct answer.
  3. To reduce the wear rate of the hinge bearings
  4. To increase the stiffness of the control surface torsion box

Explanation

Flutter is a self-excited oscillation in which aerodynamic, inertial, and elastic forces couple; it is strongly influenced by the position of the control surface centre of gravity relative to the hinge line. Mass balancing moves the centre of gravity forward so that inertia does not drive the surface to increasing deflection, raising the flutter speed.

Question 30Aircraft Structures and Airframe Systems

Which structural element in a pressurised fuselage transfers the pressure load from the skin into the adjacent frame?

  1. The frame
  2. The stringer
  3. The floor beam
  4. The shear tie Correct answer.

Explanation

A shear tie is the small connecting fitting that joins the skin or stringer to the frame, carrying the radial pressure reaction into the frame so the frame can react it as hoop tension or compression. Without shear ties the skin would be unsupported between frames and would bulge.

Question 31Aircraft Propulsion Systems

In a turbofan engine, what does the bypass ratio describe?

  1. The ratio of exhaust gas velocity to free-stream velocity
  2. The ratio of turbine inlet temperature to compressor outlet temperature
  3. The ratio of air flowing through the fan duct to air flowing through the core Correct answer.
  4. The ratio of compressor discharge pressure to ambient pressure

Explanation

Bypass ratio is the mass flow of air passing through the fan duct divided by the mass flow entering the engine core. It is a defining cycle parameter that strongly influences propulsive efficiency and specific fuel consumption. High-bypass designs move large air masses at modest velocity, which is efficient at subsonic cruise.

Question 32Aircraft Propulsion Systems

Which engine type produces essentially all of its thrust from the momentum of exhaust gases leaving a convergent nozzle, with no bypass duct?

  1. High-bypass turbofan
  2. Turbojet Correct answer.
  3. Turboshaft
  4. Turboprop

Explanation

A turbojet accelerates all of its airflow through the core and expels it through a nozzle, so thrust comes from exhaust momentum. Turbofans add a bypass stream, while turboshaft and turboprop engines extract shaft power to drive a propeller or rotor. This makes the turbojet the pure reaction-thrust machine among the choices.

Question 33Aircraft Propulsion Systems

In a gas turbine compressor, what is the primary consequence of blade fouling by dirt and oil deposits?

  1. Higher compressor exit temperature at constant speed
  2. Increased mass flow and higher surge margin
  3. Reduced pressure ratio and lower efficiency Correct answer.
  4. Reduced axial velocity through the first stage

Explanation

Fouling roughens blade surfaces and alters airfoil shape, which lowers aerodynamic efficiency and reduces the achievable pressure ratio. Mass flow typically falls and fuel burn rises for the same thrust. Compressor washes are used to restore performance.

Question 34Aircraft Propulsion Systems

What is the function of the combustor diffuser located between the compressor outlet and the combustion zone?

  1. To accelerate air so flame speed matches flow speed
  2. To mix fuel vapor with bypass air
  3. To decelerate air and recover static pressure before combustion Correct answer.
  4. To cool the turbine nozzle guide vanes

Explanation

The diffuser slows the high-velocity compressor discharge air, converting dynamic pressure into static pressure. This reduces pressure loss in the combustor and creates flow conditions stable enough for combustion. Flame stabilization is then handled by the recirculation zone, not by accelerating the flow.

Question 35Aircraft Propulsion Systems

Which material property is most critical for turbine blades operating in the high-pressure turbine?

  1. High thermal conductivity
  2. High creep resistance at elevated temperature Correct answer.
  3. Low density combined with high ductility
  4. High electrical resistivity

Explanation

HP turbine blades operate under centrifugal load at temperatures near or above their alloy's melting range, so resistance to time-dependent creep deformation governs life. Nickel superalloys with directional or single-crystal structures are used for this reason. Thermal barrier coatings and cooling further extend capability.

Question 36Aircraft Propulsion Systems

What is the purpose of the accessory gearbox on a turbofan engine?

  1. To reduce fan speed relative to the low-pressure turbine
  2. To mount and drive pumps, generators, and starters from a shaft Correct answer.
  3. To provide thrust reversal during landing rollout
  4. To control the variable geometry of the exhaust nozzle

Explanation

The accessory gearbox takes a drive from an engine shaft and distributes mechanical power to accessories such as fuel pumps, oil pumps, hydraulic pumps, generators, and the starter. It is a power take-off and mounting structure rather than an aerodynamic component.

Question 37Aircraft Propulsion Systems

During a normal engine start, what does a hung start typically indicate?

  1. The engine experiences an immediate flameout after fuel introduction
  2. The engine accelerates past idle and exceeds the start temperature limit
  3. The engine lights off but the starter fails to disengage
  4. The engine accelerates slower than scheduled and stabilizes below idle Correct answer.

Explanation

A hung start is a start in which the engine lights and runs but fails to accelerate to idle, stabilizing at a lower speed. Causes include weak starter performance, low bleed pressure, or fuel scheduling faults. The crew must abort the start to avoid overheating the turbine.

Question 38Aircraft Propulsion Systems

What is the primary reason turbine engines use air-cooled nozzle guide vanes and blades?

  1. To reduce the weight of the turbine rotor
  2. To allow operation at gas temperatures above the material limit Correct answer.
  3. To improve the compressor surge margin
  4. To increase the exhaust gas velocity

Explanation

Cooling air bled from the compressor forms a protective film and internal convection path, keeping metal temperature below the alloy limit while gas temperature exceeds it. This permits higher turbine inlet temperature and therefore greater specific thrust and efficiency. Cooling costs some cycle efficiency because the bleed air does no turbine work.

Question 39Aircraft Propulsion Systems

An engine's compressor map shows the surge line to the left of the operating line. What happens if the operating point crosses the surge line during a rapid throttle increase?

  1. The compressor flow reverses momentarily with a loud bang and possible damage Correct answer.
  2. The compressor efficiency rises sharply and thrust increases
  3. The fuel control unit automatically increases fuel flow
  4. The turbine inlet temperature falls below the limit

Explanation

Crossing the surge line means the compressor cannot sustain the pressure ratio at that flow, so the flow breaks down and reverses briefly. This produces the characteristic bang and can damage blades through aerodynamic and thermal loads. Bleed valves and variable stator vanes are used to keep the operating point clear of the surge line during transients.

Question 40Aircraft Propulsion Systems

A twin-spool turbofan has its low-pressure turbine driving the fan through a shaft that passes concentrically inside the high-pressure spool. Which statement correctly describes the spool arrangement?

  1. The HP spool drives the fan while the LP spool drives the HP compressor
  2. The LP compressor is driven by the HP turbine through a gearbox
  3. The LP and HP spools rotate at the same speed because they share one shaft
  4. The LP spool rotates independently at a lower speed than the HP spool Correct answer.

Explanation

In a twin-spool design the LP compressor/fan and LP turbine form one rotor on an inner shaft, while the HP compressor and HP turbine form a separate rotor on a concentric outer shaft. Each spool runs at its own optimum speed, which improves matching and efficiency. The shafts are mechanically independent.

Question 41Aircraft Propulsion Systems

Why does a high-bypass turbofan generally have lower specific fuel consumption than a low-bypass turbofan at subsonic cruise?

  1. It operates at a higher turbine inlet temperature for the same thrust
  2. It has a higher exhaust velocity and greater jet kinetic energy loss
  3. It eliminates the need for a high-pressure compressor
  4. It accelerates a larger mass of air to a lower velocity, improving propulsive efficiency Correct answer.

Explanation

Propulsive efficiency improves as exhaust velocity approaches flight velocity, so moving a large mass of air slowly is more efficient than moving a small mass quickly. High bypass ratio achieves this by directing most flow through the fan duct. The core still provides the energy, but the fan does most of the thrust work.

Question 42Aircraft Propulsion Systems

What is the effect of opening compressor bleed valves during low-power operation?

  1. It increases turbine inlet temperature for the same fuel flow
  2. It increases the fan pressure ratio at idle
  3. It reduces compressor delivery pressure and increases surge margin Correct answer.
  4. It raises the operating pressure ratio and moves the point closer to surge

Explanation

Bleeding air from an intermediate compressor stage reduces the mass flow that must pass through downstream stages, lowering the pressure ratio they develop. This moves the operating point away from the surge line at low corrected speeds, where the rear stages are prone to stalling. The valves close as speed increases and the margin improves naturally.

Question 43Aircraft Propulsion Systems

A turboprop engine is operating at constant power while flight speed increases. How does propeller efficiency behave as the advance ratio rises toward its optimum?

  1. It decreases monotonically from zero airspeed onward
  2. It increases to a peak and then falls as blade compressibility effects grow Correct answer.
  3. It remains constant because power is held constant
  4. It increases without limit as speed rises

Explanation

Propeller efficiency rises with advance ratio up to a design peak, because the blade angle of attack relative to the incoming air approaches an efficient value. Beyond the optimum, the blade tips approach the speed of sound, drag rises sharply, and efficiency falls. This is why propellers are matched to a design cruise Mach number.

Question 44Aircraft Propulsion Systems

What is the purpose of a fuel-oil heat exchanger in a turbofan engine fuel system?

  1. To separate water from fuel before it reaches the fuel control unit
  2. To use fuel as a heat sink to cool engine oil while warming the fuel Correct answer.
  3. To cool the fuel below its freeze point before combustion
  4. To increase fuel viscosity for better metering

Explanation

The fuel-oil heat exchanger transfers heat from hot engine oil into the fuel, cooling the oil to a safe viscosity and warming the fuel to prevent ice formation in the filter. This recovers heat that would otherwise be rejected overboard. Fuel is a convenient heat sink because it is ultimately burned.

Question 45Aircraft Propulsion Systems

In a full-authority digital engine control system, what is the role of the hydromechanical backup?

  1. It schedules variable stator vane position during acceleration
  2. It controls the thrust reverser actuation sequence
  3. It provides thrust scheduling under normal digital operation
  4. It maintains safe limited operation if the electronic control fails Correct answer.

Explanation

FADEC systems typically include a hydromechanical unit that can meter fuel and maintain a safe, limited operating mode if the electronic channel fails. Full scheduling authority resides with the digital control during normal operation. The backup protects against loss of thrust control rather than restoring full envelope performance.

Question 46Aircraft Propulsion Systems

What does a negative thrust reverser indication during the deploy sequence most likely reveal?

  1. The reverser has automatically stowed due to high airspeed
  2. One or more reverser elements failed to reach the deployed position Correct answer.
  3. The reverser has fully deployed and locked
  4. The engine has exceeded its maximum reverse thrust limit

Explanation

Reverser position feedback compares commanded and actual positions; a negative indication means at least one element has not reached the commanded state. This can result from an actuation fault, a lock failure, or an interlock preventing deployment. The crew must treat it as an abnormal configuration and follow the checklist.

Question 47Aircraft Propulsion Systems

Why is a single-crystal nickel superalloy preferred over an equiaxed casting for high-pressure turbine blades?

  1. It eliminates grain boundaries that act as creep and fatigue crack initiation sites Correct answer.
  2. It provides higher thermal conductivity to protect the blade root
  3. It has a lower melting temperature that simplifies casting
  4. It allows the blade to be manufactured without cooling passages

Explanation

Grain boundaries are weak paths for creep rupture and thermal fatigue at high temperature, so removing them improves rupture life. Directional solidification aligns grains along the span, and single-crystal casting removes them entirely. This allows higher metal temperatures or longer life for the same cooling.

Question 48Aircraft Propulsion Systems

What is the primary effect of tip clearance on compressor performance?

  1. It increases mass flow at constant speed
  2. It causes leakage over the blade tip that reduces efficiency and pressure rise Correct answer.
  3. It eliminates the need for variable stator vanes
  4. It lowers the compressor exit temperature at constant pressure ratio

Explanation

Pressure differences between the pressure and suction surfaces drive flow over the blade tip, creating a leakage vortex that disturbs the passage flow. The result is lost work, reduced pressure rise, and lower efficiency. Active clearance control systems manage casing growth to minimize this gap.

Question 49Aircraft Propulsion Systems

A turbofan experiences an engine surge during acceleration from idle. Which corrective action is appropriate for the flight crew?

  1. Advance the throttle further to push through the surge
  2. Reduce thrust and follow the engine surge or stall checklist Correct answer.
  3. Shut down the engine immediately in all cases
  4. Increase bleed air extraction to the cabin

Explanation

The standard response is to reduce power, which lowers the operating pressure ratio and helps the compressor recover. The crew then follows the manufacturer's surge or stall procedure, which may include an in-flight restart or a precautionary shutdown depending on symptoms. Advancing the throttle would worsen the condition.

Question 50Aircraft Propulsion Systems

Why does a turboshaft engine use a free power turbine rather than driving the main rotor directly from the gas generator spool?

  1. It increases the gas generator's compression ratio
  2. It allows the rotor system to operate at a speed independent of the gas generator Correct answer.
  3. It eliminates the need for a reduction gearbox
  4. It permits the use of a centrifugal compressor

Explanation

A free power turbine is aerodynamically coupled to, but mechanically independent of, the gas generator. This decouples rotor speed from gas generator speed, which improves part-power efficiency and allows the rotor to autorotate if the engine fails. A reduction gearbox is still required because turbine speed is far above rotor speed.