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CPL AGK / Systems practice questions

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Question 1Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

On a semi-monocoque fuselage, what is the primary function of the frames (formers) as distinct from the stringers?

  1. They carry the principal bending loads along the length of the fuselage.
  2. They seal the pressure cabin and act as the primary pressure bulkheads.
  3. They maintain the cross-sectional shape and support the skin, while longitudinal loads are carried mainly by the stringers and skin. Correct answer.
  4. They provide the attachment points for the wing spar carry-through structure only.

Explanation

Frames are transverse members that hold the fuselage cross-section to shape and stabilise the skin against buckling, while longitudinal bending and shear loads are carried primarily by the stringers working with the stressed skin. Pressure sealing is a function of the skin and dedicated bulkheads, not of ordinary frames.

Question 2Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

Why are wing skins on transport aircraft often machined from thick plate with integral stringers rather than built from thin sheet riveted to separate stringers?

  1. It removes the requirement for a torsion box in the wing.
  2. It allows the wing to be assembled without jigs or tooling.
  3. It eliminates the need for any internal wing structure such as ribs.
  4. It reduces the number of fasteners and splices, improving fatigue life and saving weight. Correct answer.

Explanation

Integrally machined skins remove thousands of rivet holes and lap joints, which are common fatigue-initiation sites, and they place material only where stress demands it, giving a lighter structure. Ribs, spars and a torsion box are still required for shape and torsional stiffness.

Question 3Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

Which structural element of a wing carries the torsional loads and gives the wing its resistance to twisting?

  1. The torsion box formed by the front and rear spars with the top and bottom skin Correct answer.
  2. The wing ribs
  3. The trailing-edge flaps
  4. The wingtip fairing

Explanation

Torsion is carried by the closed cell formed between the front and rear spars and the upper and lower skins, commonly called the torsion box. Ribs maintain shape and transfer loads, while flaps and tip fairings are not primary torsional structure.

Question 4Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

What is the main structural purpose of the empennage's horizontal stabiliser attachment to the fuselage?

  1. To transmit pitch control loads and stabiliser loads into the fuselage structure. Correct answer.
  2. To provide the primary attachment for the wing spar carry-through.
  3. To house the aircraft's main fuel tanks.
  4. To carry the vertical fin bending loads only.

Explanation

The horizontal stabiliser attachment must transfer the lift and pitching loads generated by the stabiliser and elevator into the fuselage frames and skin. Wing carry-through and fin loads are handled by their own dedicated attachments.

Question 5Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

A control surface is described as mass-balanced. What does this mean?

  1. Its total weight has been reduced to the minimum permitted by the manufacturer.
  2. It is trimmed to neutral by the pilot before each flight.
  3. Its weight is concentrated ahead of the hinge line so that its centre of gravity lies forward of the hinge. Correct answer.
  4. It is balanced aerodynamically by an equal surface on the opposite side.

Explanation

Mass balancing places weight ahead of the hinge line so the surface's centre of gravity is at or forward of the hinge, which prevents flutter by removing the inertia-driven oscillation. It is a fixed design feature, not a pilot trimming action.

Question 6Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

Why is an aileron often fitted with a horn balance or an inset hinge?

  1. To increase the maximum available aileron deflection.
  2. To increase the flutter speed by moving the centre of gravity aft.
  3. To provide a mechanical stop against over-travel.
  4. To reduce the hinge moment required from the pilot or actuator at large deflections. Correct answer.

Explanation

Aerodynamic balancing methods such as horn balances or inset hinges reduce the hinge moment by allowing aerodynamic pressure to assist the deflection, lowering control forces. They do not move the centre of gravity aft, which would be detrimental to flutter.

Question 7Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

In a manual (unassisted) flight control system, what is the function of the cable tension regulator?

  1. To maintain a constant cable tension as the aircraft structure expands and contracts with temperature. Correct answer.
  2. To limit the maximum control surface deflection.
  3. To increase the mechanical advantage of the control column.
  4. To lubricate the cables during operation.

Explanation

Cable tension regulators use spring-loaded quadrants to keep tension within limits as the airframe changes dimension with temperature and loading, preventing slack or over-tension. They do not change mechanical advantage or travel limits.

Question 8Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

What is the purpose of a follow-up (feedback) linkage in a powered flight control system?

  1. It returns the control surface to neutral if the actuator jams.
  2. It locks the control surface when the hydraulic system is off.
  3. It positions the control surface in proportion to control input and gives control feel. Correct answer.
  4. It increases hydraulic pressure at large control deflections.

Explanation

The follow-up linkage feeds surface position back to the control valve so that the surface deflection is proportional to the input and the control stops moving when the input stops. It also contributes to the artificial feel of the system.

Question 9Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

An aircraft has fully powered flight controls with no manual reversion. What is the significance of this for handling after a total hydraulic failure?

  1. The controls become heavier but remain fully usable.
  2. The controls revert to trim tabs for pitch and roll only.
  3. The controls remain fully effective because of aerodynamic balance.
  4. The controls are lost, so the system design must prevent total loss of hydraulic power. Correct answer.

Explanation

With no manual reversion the pilot cannot move the surfaces without hydraulic power, so certification requires redundancy such as multiple independent hydraulic systems to make total failure extremely improbable. Handling after total failure is not a graceful degradation but loss of control.

Question 10Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

What is the primary function of a wing spar?

  1. To contain the fuel and vent it during flight.
  2. To carry the bending moments and shear forces generated by wing lift. Correct answer.
  3. To attach the ailerons to the wing.
  4. To provide the aerofoil contour between the ribs.

Explanation

The spar is the main longitudinal beam of the wing, with caps carrying bending and the web carrying shear. Skins and ribs maintain the aerodynamic shape, and control surfaces are attached through dedicated hinges and brackets.

Question 11Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

Why are some transport aircraft fitted with a ventral fin or a dorsal fin extension?

  1. To provide additional mounting area for the horizontal stabiliser.
  2. To balance the aircraft longitudinally in the cruise.
  3. To increase directional stability and reduce the risk of fin stall at high angles of attack. Correct answer.
  4. To increase the maximum cruise speed by reducing drag.

Explanation

Additional fin area such as a dorsal fin or ventral fin improves directional stability and helps maintain fin effectiveness at high angles of attack, reducing the risk of fin stall and loss of directional control. They are not primarily drag-reduction or trim devices.

Question 12Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

What is the role of the pressure bulkheads in a pressurised fuselage?

  1. They close the pressure vessel at the front and rear and carry the resulting pressure loads. Correct answer.
  2. They provide attachment for the passenger seats.
  3. They divide the cabin into compartments to control temperature.
  4. They support the cabin floor beams only.

Explanation

Pressure bulkheads seal the ends of the pressurised section and react the large differential pressure loads, transferring them into the fuselage structure. Temperature zoning and seat attachment are unrelated functions.

Question 13Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

During a walk-around, a pilot notices that a wing skin panel shows a row of loose rivets with slight working around the holes. Why is this significant?

  1. It is normal for integral machined skins and needs no action.
  2. Loose fasteners allow load to bypass the joint, causing stress concentration and possible crack growth. Correct answer.
  3. It only affects the aerodynamic smoothness and slightly increases drag.
  4. It indicates the fuel tank is over-pressurised.

Explanation

Loose rivets redistribute load into fewer fasteners and the surrounding skin, raising local stress and creating a fatigue-crack initiation site. Aerodynamic drag is a minor issue compared with the structural implication.

Question 14Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

What is the purpose of the stall strips fitted to the leading edge of some wings?

  1. To increase the maximum lift coefficient of the wing.
  2. To ensure the wing root stalls before the tip, preserving aileron effectiveness. Correct answer.
  3. To reduce the wing's drag at high speed.
  4. To protect the leading edge from bird strikes.

Explanation

Stall strips are small angular devices that trigger early local stall at the inboard section, so the root stalls first and the ailerons near the tips remain effective. They do not increase maximum lift or reduce high-speed drag.

Question 15Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

How does a spring tab assist the pilot on a large control surface?

  1. It provides a fixed bias so the aircraft flies hands-off at one speed.
  2. It acts as a mass balance ahead of the hinge line.
  3. It locks the surface when the pilot releases the controls.
  4. It uses aerodynamic force on a small tab to help move the main surface when control forces are high. Correct answer.

Explanation

A spring tab is deflected through a spring when control forces rise, and the resulting tab hinge moment assists movement of the main surface, reducing pilot effort at high speed. It is not a fixed trim bias or a mass balance.

Question 16Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

Which statement best describes the load path for elevator loads in a conventional tailplane?

  1. Elevator hinge loads pass into the tailplane rear spar and ribs, then through the stabiliser attachments into fuselage frames. Correct answer.
  2. Elevator loads pass directly into the fin and then into the fuselage.
  3. Elevator loads are carried only by the elevator actuator and not by the structure.
  4. Elevator loads are transmitted to the wing through the rear fuselage.

Explanation

Hinge loads from the elevator are collected by the tailplane structure, mainly the rear spar and ribs, and then transferred through the stabiliser attachment fittings into fuselage frames. The fin and wing are not part of this primary path.

Question 17Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

What is the function of the aileron-rudder interconnect found on some aircraft?

  1. It prevents the pilot from applying rudder and aileron in opposite directions.
  2. It automatically trims the aircraft in pitch during turns.
  3. It locks the rudder when the autopilot is engaged.
  4. It applies rudder with aileron input to counter adverse yaw and coordinate turns. Correct answer.

Explanation

The interconnect feeds a proportional rudder deflection when ailerons are applied, helping to overcome adverse yaw and keep turns coordinated. It assists rather than forbids opposite inputs and does not act in pitch.

Question 18Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

Why must a control surface with a large overhanging balance ahead of the hinge be carefully checked for correct mass balance after repainting?

  1. Paint always increases the hinge moment beyond the actuator limit.
  2. Paint changes the aerodynamic contour and invalidates the type certificate.
  3. Added weight ahead of the hinge reduces the effectiveness of the surface.
  4. Added weight behind the hinge can move the centre of gravity aft and reduce flutter margin. Correct answer.

Explanation

Repainting adds weight, and if material is added aft of the hinge it can move the surface centre of gravity rearward, eroding the mass-balance margin and lowering the flutter speed. Mass balance must therefore be verified after painting or repair.

Question 19Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

What is the purpose of the wing-to-fuselage attachment fittings being designed as failsafe or multiple-load-path structures?

  1. To permit the wing to flex freely without transferring loads.
  2. So that a single failed fitting does not cause loss of the wing, allowing the defect to be found before failure. Correct answer.
  3. To reduce the weight of the wing by eliminating the spar.
  4. To allow the wing to be removed quickly for transport.

Explanation

Failsafe design provides alternate load paths so that a crack or failure in one element is detected during inspection before it progresses to catastrophic failure. Quick removal, spar elimination and free flexing are not the objectives.

Question 20Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

What is the primary purpose of the trim system on a powered aircraft?

  1. To provide redundancy if the primary controls fail.
  2. To relieve steady control forces so the aircraft can be flown hands-off at a chosen speed and configuration. Correct answer.
  3. To increase the maximum rate of control surface deflection.
  4. To lock the controls during parking.

Explanation

Trim applies a steady bias to the control system so the pilot does not have to hold continuous force in steady flight, allowing hands-off operation at the trimmed condition. It does not increase deflection rate or serve as a backup control path.

Question 21Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

Aircraft with irreversible powered controls often include artificial feel. Why is this necessary?

  1. Because the control surfaces would otherwise flutter.
  2. Because irreversible controls are lighter than reversible ones.
  3. Because the hydraulic system cannot provide enough force to move the surfaces.
  4. Because the pilot receives no natural aerodynamic feedback through the controls, so feel must be generated artificially. Correct answer.

Explanation

In an irreversible system the surface loads are not fed back to the pilot, so without artificial feel the controls would move with no resistance and the pilot could overstress the aircraft. Artificial feel restores a force that varies with speed and deflection.

Question 22Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

What structural feature allows a wing with integral fuel tanks to carry fuel without a separate bladder?

  1. Sealed joints and sealant applied to the internal structure of the wing box. Correct answer.
  2. A pressurised compartment vented to the cabin.
  3. A rubber bladder bonded to the outer skin.
  4. A separate aluminium tank mounted inside the wing.

Explanation

Integral tanks use the wing box itself as the container, with the structure sealed at joints and fasteners using fuel-resistant sealant. This saves the weight and volume of a separate bladder or tank.

Question 23Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

What is the purpose of vortex generators on a wing or control surface?

  1. To reduce the wing's structural weight.
  2. To provide additional mass balance for the ailerons.
  3. To energise the boundary layer and delay flow separation at high angles of attack. Correct answer.
  4. To generate lift at zero airspeed.

Explanation

Vortex generators add kinetic energy to the boundary layer, keeping it attached longer and delaying separation, which improves control effectiveness at high angles of attack. They do not create lift at zero airspeed or affect structural weight.

Question 24Airframe and structural systems: fuselage, wings, empennage, flight controls and their actuation

Why is the fin of a transport aircraft often attached with a failsafe joint designed to carry loads through multiple fittings?

  1. To reduce the fin's contribution to directional stability.
  2. To permit the fin to flex and reduce rudder effectiveness.
  3. To allow the fin to be removed for routine washing.
  4. To ensure that loss of one attachment does not allow the fin to separate before the defect is detected. Correct answer.

Explanation

Multiple-load-path fittings make the fin attachment failsafe, so a single crack or failed bolt does not lead to loss of the fin before inspection finds it. Removal for washing, deliberate flexing and reduced stability are not design intentions.

Question 25Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

In a typical aircraft hydraulic system, what is the primary function of the reservoir?

  1. To filter out fine particles before the fluid returns to the pump
  2. To convert hydraulic pressure into mechanical force
  3. To pressurise the fluid before it reaches the engine-driven pump
  4. To store fluid, allow for thermal expansion and provide a place for air to separate from the fluid Correct answer.

Explanation

The reservoir holds the system fluid, absorbs the volume changes caused by temperature and actuator movement, and gives entrained air and contaminants a chance to settle out. It is a storage and conditioning component, not a pressure source or a filter.

Question 26Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

What is the main purpose of a pressure accumulator in an aircraft hydraulic system?

  1. To remove water contamination from the hydraulic fluid
  2. To increase the maximum flow rate produced by the engine-driven pump
  3. To cool the fluid returning from the actuators
  4. To store pressurised fluid energy for peak demands and to damp pressure surges Correct answer.

Explanation

An accumulator stores energy in a compressed gas or spring and releases it when demand briefly exceeds pump output, and it absorbs pressure pulsations and thermal expansion. It supplements the pump rather than replacing it.

Question 27Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

In a hydraulic system, what does a pressure relief valve do?

  1. It limits maximum system pressure by diverting fluid back to return Correct answer.
  2. It prevents reverse flow when the pump stops
  3. It isolates a failed circuit from the rest of the system
  4. It maintains a constant reduced pressure downstream of the valve

Explanation

A relief valve opens at a set pressure and bypasses fluid to return, protecting components from overpressure. It is a safety device that normally stays closed during ordinary operation.

Question 28Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

Which component converts hydraulic pressure into linear mechanical movement?

  1. A shuttle valve
  2. An accumulator
  3. A double-acting cylinder Correct answer.
  4. A gear pump

Explanation

A cylinder is a linear actuator: pressurised fluid acting on the piston area produces force and stroke. Pumps create flow, accumulators store energy, and valves direct or control flow.

Question 29Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

What is the purpose of a hydraulic system pressure gauge on the cockpit panel?

  1. To indicate the quantity of fluid remaining in the reservoir
  2. To display the temperature of the fluid returning to the reservoir
  3. To confirm that the parking brake is mechanically engaged
  4. To show the selected system pressure so the crew can detect pump or regulator faults Correct answer.

Explanation

The pressure gauge displays the pressure in the selected system and lets the crew verify normal pump and regulator operation or identify a failure. Quantity and temperature are shown by separate indicators.

Question 30Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

Why must hydraulic fluid be able to separate readily from entrained air in the reservoir?

  1. Because air bubbles cause a spongy response and can lead to pump cavitation Correct answer.
  2. Because entrained air reduces fluid compressibility
  3. Because air in the fluid increases the fluid's lubricity
  4. Because air improves the sealing of actuator pistons

Explanation

Air entrained in hydraulic fluid makes the system response spongy, reduces effective bulk modulus, and can cause cavitation damage in pumps. A reservoir with adequate dwell time and baffles allows the air to rise out before the fluid is drawn into the pump.

Question 31Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

An engine-driven hydraulic pump has failed in flight, but the system pressure remains normal for a period. Which component most likely accounts for this?

  1. The return filter has bypassed
  2. The accumulator is supplying stored fluid to the system Correct answer.
  3. The pressure relief valve has opened fully
  4. The reservoir is overfilled

Explanation

A charged accumulator can supply a limited volume of pressurised fluid after pump failure, allowing a few operations before pressure decays. Relief valve opening, filter bypass, or overfilling do not substitute for lost pump output.

Question 32Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

During a pre-flight check the crew notices the hydraulic reservoir quantity is at the low limit but the system pressure is normal. What is the most appropriate interpretation?

  1. Low quantity may reduce the fluid available for thermal expansion and leak margin, so it must be corrected per the maintenance manual Correct answer.
  2. The quantity indication is certainly faulty because pressure is normal
  3. The accumulator must be pre-charged to a higher pressure to compensate
  4. The system can be dispatched because pressure is the only limiting factor

Explanation

Normal pressure only shows the pump is delivering; it says nothing about the reserve needed for thermal expansion, leakage, and accumulator replenishment. Low quantity must be serviced to the specified level before flight.

Question 33Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

A hydraulic system uses a variable-displacement pump with a pressure compensator. As system pressure approaches the set value with no demand, what happens?

  1. Pump displacement is increased to build pressure faster
  2. Pump displacement is reduced toward zero to limit pressure and power Correct answer.
  3. The relief valve opens continuously to dump all pump output
  4. The accumulator is isolated and the pump stops rotating

Explanation

A pressure-compensated pump reduces its displacement as the set pressure is reached, so flow falls to near zero and pressure is held without dumping fluid. This saves power and reduces heat compared with a fixed pump relying on a relief valve.

Question 34Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

What is the function of a check valve in a hydraulic system?

  1. To regulate flow rate to a constant value
  2. To reduce system pressure to a lower constant value
  3. To permit flow in one direction only and prevent reverse flow Correct answer.
  4. To select the higher of two pressure sources

Explanation

A check valve is a one-way valve that allows free flow in the permitted direction and blocks reverse flow, protecting the pump and holding pressure in parts of the system. Flow regulation and pressure reduction are performed by other valves.

Question 35Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

A hydraulic actuator moves slowly and erratically when the system is cold, then improves as it warms up. Which explanation is most likely?

  1. The relief valve setting is too low when cold
  2. The fluid viscosity is high when cold, increasing flow resistance until it thins with temperature Correct answer.
  3. The return filter is bypassing when cold
  4. The accumulator pre-charge is too high when cold

Explanation

Cold hydraulic fluid has high viscosity, so pressure losses in lines and valves rise and flow to the actuator is reduced. As the fluid warms and viscosity falls, flow improves and the actuator moves normally.

Question 36Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

What is the role of a selector valve in a hydraulic system?

  1. To limit the maximum pressure in the system
  2. To direct pump output to the chosen actuator or circuit Correct answer.
  3. To indicate fluid quantity in the reservoir
  4. To store pressurised fluid for peak demand

Explanation

A selector valve routes pressurised fluid to the selected actuator, such as landing gear or flaps, and directs return fluid back to the reservoir. It is a directional-control device.

Question 37Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

An accumulator is pre-charged with nitrogen to 1000 psi and the system operates at 3000 psi. What happens to the gas as system pressure rises from zero to 3000 psi?

  1. The gas dissolves completely in the hydraulic fluid
  2. The gas is vented overboard to make room for fluid
  3. The gas pressure stays at 1000 psi while the fluid volume changes
  4. The gas is compressed and its pressure rises toward system pressure as fluid enters Correct answer.

Explanation

As fluid enters the accumulator, it compresses the gas until gas pressure equals system pressure. The pre-charge sets the starting point, and the gas volume change provides the usable stored fluid.

Question 38Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

Why are hydraulic reservoirs often pressurised slightly with bleed air or nitrogen?

  1. To prevent pump cavitation at high altitude by maintaining a positive inlet head Correct answer.
  2. To eliminate the need for a relief valve
  3. To increase the maximum system operating pressure
  4. To reduce the viscosity of the fluid

Explanation

Slight pressurisation raises the pressure at the pump inlet above the fluid's vapour pressure, which prevents cavitation when ambient pressure is low at altitude. It also helps force fluid to the pump.

Question 39Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

A hydraulic pump is described as a positive-displacement type. What does this mean?

  1. It delivers a nearly fixed volume of fluid per revolution, largely independent of outlet pressure Correct answer.
  2. It delivers a flow that falls in proportion to rising outlet pressure
  3. It produces pressure directly and flow follows demand
  4. It requires no inlet fluid and draws from the reservoir by suction alone

Explanation

A positive-displacement pump traps a fixed volume of fluid per cycle and forces it into the outlet, so output flow is set mainly by speed. If the outlet is blocked, pressure rises until the relief valve acts.

Question 40Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

A hydraulic system shows normal pressure but an actuator extends sluggishly while other actuators operate normally. Which fault is most likely?

  1. The engine-driven pump is worn
  2. The selector valve or line serving that actuator is restricted Correct answer.
  3. The system relief valve is set too low
  4. The reservoir is low on fluid

Explanation

If pressure is normal and other actuators work correctly, the fault is local to the affected circuit, such as a partly closed selector valve, a kinked line, or a restricted orifice. System-wide faults would affect all users.

Question 41Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

In a hydraulic system fitted with a pressure-reducing valve feeding a sensitive circuit, what does the valve do when the downstream pressure reaches its setting?

  1. It closes the inlet to hold downstream pressure at the set value Correct answer.
  2. It reverses flow to the reservoir
  3. It opens fully and dumps all flow to return
  4. It increases downstream pressure to match the main system

Explanation

A pressure-reducing valve throttles or closes the inlet as downstream pressure reaches the set value, maintaining a constant lower pressure for that circuit. It does not dump flow to return like a relief valve.

Question 42Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

Hydraulic fluid in a reservoir is found to be milky or cloudy. What is the most likely cause and consequence?

  1. Normal aeration seen only in cold weather
  2. Excessive nitrogen pre-charge in the accumulator
  3. Water contamination, which can cause corrosion and loss of lubricity Correct answer.
  4. Air entrainment, which improves system stiffness

Explanation

A milky appearance indicates water contamination, which promotes corrosion, reduces lubricity, and can cause erratic operation or freezing at altitude. The fluid should be sampled and the system serviced per maintenance instructions.

Question 43Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

An aircraft has two independent hydraulic systems, and one system's pressure gauge reads zero while the other is normal. What is the most appropriate crew action?

  1. Identify the affected system and apply the relevant abnormal procedure, since some services may be lost Correct answer.
  2. Assume the gauge is faulty and continue normally
  3. Cross-connect the systems and continue
  4. Increase pump speed to restore pressure

Explanation

Loss of pressure in one system means the services powered by that system may be unavailable, so the crew must identify the affected system and follow the approved abnormal checklist. Cross-connecting or ignoring the indication is not appropriate.

Question 44Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system monitoring

A hydraulic system uses an accumulator pre-charged to 1000 psi with a system pressure of 3000 psi. After a pump failure, pressure falls rapidly once a small volume has been used. What does this indicate?

  1. The accumulator pre-charge is too high, so the gas volume is too small Correct answer.
  2. The accumulator pre-charge is too low, so little usable fluid is stored
  3. The relief valve is stuck closed
  4. The reservoir is overfilled

Explanation

If pre-charge is too high, the gas occupies little volume at system pressure, so only a small amount of fluid can be stored and pressure collapses quickly after pump loss. Correct pre-charge leaves enough gas volume to provide usable emergency supply.

Question 45Pneumatic and air-conditioning systems: bleed air, pressurisation, cabin environment

In a transport-category aircraft, cabin pressurisation is normally achieved by supplying conditioned air to the cabin while regulating the rate at which air leaves through which component?

  1. The air-conditioning pack turbine bypass valve
  2. The negative-pressure relief valve
  3. The bleed-air pressure regulator valve
  4. The cabin pressure controller driving the outflow valve Correct answer.

Explanation

The cabin is kept at a controlled pressure by balancing the inflow of conditioned air against the controlled escape of air through the outflow valve. The pressure controller commands the outflow valve position to hold the selected cabin altitude and rate of change. Relief valves are safety devices that operate only when limits are exceeded.

Question 46Pneumatic and air-conditioning systems: bleed air, pressurisation, cabin environment

During cruise, the cabin altitude of a pressurised aircraft is normally maintained at which level relative to the aircraft's actual altitude?

  1. An altitude that varies randomly with engine power
  2. An altitude equal to the aircraft's altitude
  3. A higher altitude than the aircraft
  4. A lower altitude than the aircraft Correct answer.

Explanation

The cabin is held at a pressure equivalent to a lower altitude than the aircraft so that occupants are not exposed to the low pressure and oxygen partial pressure of high cruise levels. The differential between cabin and ambient pressure is limited by the structural design. This is why the cabin altitude indicator reads lower than the actual flight level.

Question 47Pneumatic and air-conditioning systems: bleed air, pressurisation, cabin environment

What is the primary function of the air-conditioning packs in a bleed-air environmental control system?

  1. To cool and condition bleed air to a breathable temperature and humidity Correct answer.
  2. To filter engine oil particles from the hydraulic fluid
  3. To increase bleed-air pressure before it enters the cabin
  4. To generate electrical power for the cabin systems

Explanation

Packs take hot, high-pressure bleed air and reduce its temperature and moisture content so it can be supplied to the cabin at a comfortable, controlled temperature. They typically use air-cycle machines with heat exchangers and a turbine. They do not raise pressure or generate electrical power.

Question 48Pneumatic and air-conditioning systems: bleed air, pressurisation, cabin environment

What is the purpose of the cabin pressure differential limit in a pressurisation system?

  1. To limit the maximum cabin temperature
  2. To prevent the outflow valve from fully closing
  3. To keep the bleed-air temperature within limits
  4. To protect the fuselage structure from excessive pressure loads Correct answer.

Explanation

Differential pressure is the difference between cabin pressure and outside ambient pressure, and it produces hoop and longitudinal loads on the fuselage. A maximum differential limit, enforced by the pressure controller and a safety relief valve, protects the structure from overstress. Temperature and valve travel are separate considerations.

Question 49Pneumatic and air-conditioning systems: bleed air, pressurisation, cabin environment

Which component prevents the cabin altitude from exceeding a safe value if the normal pressure controller fails to modulate the outflow valve?

  1. The bleed-air fan-air valve
  2. The cabin recirculation fan
  3. The pack turbine bypass valve
  4. The cabin altitude warning and the positive-pressure relief valve Correct answer.

Explanation

A positive-pressure relief valve opens automatically if cabin differential pressure reaches the structural limit, providing an independent safeguard against overpressure. A cabin altitude warning alerts the crew when cabin pressure is inadequate. Neither the turbine bypass valve nor the recirculation fan provides this protection.

Question 50Pneumatic and air-conditioning systems: bleed air, pressurisation, cabin environment

An aircraft is climbing and the cabin vertical-speed indicator shows a rate of change greater than the selected schedule. Which action of the pressure controller best explains this?

  1. The controller has opened the negative-pressure relief valve
  2. The controller has closed the pack bypass valves to warm the cabin
  3. The controller has fully opened the bleed valves to increase inflow
  4. The controller is modulating the outflow valve to hold the selected cabin rate Correct answer.

Explanation

The pressure controller continuously compares actual cabin altitude and rate with the selected schedule and repositions the outflow valve to keep the rate within limits. An excessive rate indicates the outflow valve is not modulating as commanded, for example because of a controller fault or a valve jam. Bleed and pack valves affect supply and temperature rather than the pressure schedule.