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Brunei DCA CPL AGK - Airframe, Systems & Power Plant study materials
Brunei DCA CPL AGK - Airframe, Systems & Power Plant study resources

Brunei DCA CPL AGK - Airframe, Systems & Power Plant practice questions

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Question 1Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

Which structural component of a semi-monocoque fuselage carries the primary bending and shear loads along the length of the aircraft?

  1. The cabin floor beams alone
  2. The decorative interior trim panels
  3. The longitudinal stringers and frames acting together with the skin Correct answer.
  4. The passenger windows and door frames

Explanation

In semi-monocoque construction the skin is reinforced by longitudinal stringers and transverse frames or bulkheads, and these elements share the bending, shear and pressurisation loads. The skin alone would buckle, so the stiffeners are essential to the load path.

Question 2Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

A bulkhead in a pressurised fuselage differs from an ordinary frame mainly because it:

  1. Is installed only in the cockpit area
  2. Closes off a pressure compartment and reacts the resulting pressure load Correct answer.
  3. Is made only from aluminium alloy
  4. Carries no loads at all

Explanation

A pressure bulkhead forms the boundary of a pressurised compartment and must react the large differential pressure force, usually as a diaphragm or dome. Ordinary frames merely maintain the shell shape and support the skin between bulkheads.

Question 3Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

In a cantilever wing, the bending moment produced by lift is greatest:

  1. At the wing root Correct answer.
  2. At the wing tip
  3. Halfway along the semi-span
  4. At the aileron hinge line

Explanation

A cantilever wing behaves like a beam fixed at the fuselage; the bending moment accumulates from tip to root and reaches its maximum at the root attachment. This is why the root structure and centre-section joints are the heaviest part of the wing.

Question 4Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

The main function of wing ribs is to:

  1. Carry the spanwise bending loads to the fuselage
  2. Provide attachment for the landing gear only
  3. Maintain the aerofoil shape and support the skin between spars Correct answer.
  4. Transmit engine thrust to the wing root

Explanation

Ribs are chordwise members that preserve the aerofoil contour, stabilise the skin and stringers, and transfer local loads such as fuel or control-surface reactions into the spars. Spanwise bending is carried mainly by the spars.

Question 5Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

A wing spar that is machined from a single billet of aluminium alloy, with integral flanges and web, is described as:

  1. A wire-braced spar
  2. An integral or machined spar Correct answer.
  3. A laminated wooden spar
  4. A built-up spar

Explanation

An integral spar is cut or machined from solid material so that flanges, web and stiffeners form one continuous piece, eliminating riveted joints and reducing weight. Built-up spars, by contrast, are assembled from separate web and boom components.

Question 6Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

The horizontal stabiliser of a conventional empennage is primarily intended to:

  1. House the main landing gear
  2. Carry the wing bending loads
  3. Generate most of the aircraft lift
  4. Provide longitudinal static and dynamic stability Correct answer.

Explanation

The horizontal stabiliser produces a downward or upward tail load that balances the wing pitching moment and gives longitudinal stability. The elevator, hinged to it, provides pitch control.

Question 7Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

An aircraft with a vertical fin having significant sweep and a horizontal tail mounted part-way up the fin is using which empennage layout?

  1. Cruciform tail Correct answer.
  2. V-tail
  3. Conventional tail
  4. T-tail

Explanation

A cruciform tail mounts the horizontal stabiliser partway up the vertical fin, keeping it clear of wing wake and propeller slipstream while avoiding the full structural penalty of a T-tail. A T-tail places the horizontal surface at the very top of the fin.

Question 8Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

The primary flight controls of a light aeroplane are:

  1. Fowler flaps and speed brakes
  2. Flaps, slats and spoilers
  3. Ailerons, elevator and rudder Correct answer.
  4. Trim tabs and balance tabs

Explanation

Primary controls move the aircraft about its three axes: ailerons in roll, elevator in pitch and rudder in yaw. Flaps, slats, spoilers and trim tabs are secondary or auxiliary controls that modify the lift or trim state.

Question 9Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

Ailerons produce a rolling moment because:

  1. They move the centre of gravity sideways
  2. They increase thrust on one side
  3. They change the wing dihedral angle
  4. They increase lift on the down-going wing and decrease it on the up-going wing Correct answer.

Explanation

Deflecting one aileron down raises lift on that wing while the opposite aileron up reduces lift, so the wing rises and the aircraft rolls. The resulting couple about the longitudinal axis is the rolling moment.

Question 10Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

Adverse yaw during a roll is best described as:

  1. The nose pitching up as flaps are lowered
  2. The tail yawing into the turn because of dihedral
  3. The nose yawing away from the direction of the intended turn Correct answer.
  4. The aircraft rolling faster than commanded

Explanation

The down-going aileron produces more induced drag on the rising wing, so the nose tends to yaw opposite to the roll direction. Pilots counter it with coordinated rudder, and designers use differential aileron travel or Frise ailerons to reduce it.

Question 11Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

A Frise aileron reduces adverse yaw because:

  1. It is balanced by a weight ahead of the hinge
  2. It moves the aileron hinge line aft of the trailing edge
  3. It increases the wing camber when deflected down
  4. Its leading edge projects below the wing when deflected up, adding drag on the down-going wing Correct answer.

Explanation

A Frise aileron has a projecting nose on its leading edge; when the aileron goes up, this nose protrudes into the airflow beneath the wing and creates drag that offsets the extra drag of the opposite down-going aileron. The result is closer to balanced yaw during a roll.

Question 12Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

An elevator fitted with a horn balance relies on:

  1. An area of the control surface ahead of the hinge exposed to the airflow Correct answer.
  2. A separate trim tab on the opposite side
  3. A spring connected to the control column
  4. A weight mounted inside the fuselage

Explanation

A horn balance is a projecting area of the control surface forward of the hinge line; the aerodynamic force on it opposes the deflection and reduces the stick force needed. It is an aerodynamic balance, not a mass balance.

Question 13Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

A trim tab on an elevator is used to:

  1. Provide flutter damping
  2. Relieve steady stick forces in a chosen flight condition Correct answer.
  3. Increase the maximum elevator deflection
  4. Lock the elevator on the ground

Explanation

The trim tab deflects in the opposite sense to the control surface and generates a small aerodynamic moment that holds the surface in the desired position without continuous pilot force. It allows hands-off flight at the selected speed and configuration.

Question 14Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

A balance tab differs from an anti-balance tab in that a balance tab:

  1. Is used only on the rudder
  2. Deflects in the opposite direction to the control surface, reducing stick force Correct answer.
  3. Deflects in the same direction as the control surface
  4. Works only when the aircraft is on the ground

Explanation

A balance tab is linked so that it moves opposite to the main surface, creating a moment that assists the pilot and lightens control forces. An anti-balance tab moves with the surface and increases the force, giving feel and preventing over-controlling.

Question 15Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

Flaps are normally extended for take-off and landing in order to:

  1. Increase the maximum lift coefficient and reduce the stalling speed Correct answer.
  2. Increase the never-exceed speed
  3. Increase the rate of climb at high altitude
  4. Reduce the wing bending moment to zero

Explanation

Flaps increase wing camber and often wing area, raising the maximum lift coefficient so that the aircraft can fly slower and use shorter runways. The price is higher drag and a lower limiting speed with flaps extended.

Question 16Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

A Fowler flap differs from a simple plain flap because it:

  1. Deflects upward to dump lift
  2. Is fitted only on the horizontal stabiliser
  3. Only changes the wing camber
  4. Moves aft on tracks as well as down, increasing both camber and wing area Correct answer.

Explanation

A Fowler flap translates rearward on tracks before deflecting downward, so it increases wing chord and area as well as camber. The combination gives a larger lift increment than a plain flap for the same deflection angle.

Question 17Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

Spoilers are used in flight primarily to:

  1. Destroy lift and increase drag, allowing a steeper descent without excessive speed Correct answer.
  2. Replace the elevator for pitch control
  3. Reduce the wing dihedral effect
  4. Increase lift at low speed

Explanation

Spoilers are panels on the upper wing surface that disrupt the smooth airflow, reducing lift and adding drag. In flight this permits a steeper descent at a given speed, and on the ground they dump lift to improve braking.

Question 18Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

A pilot rolls the aircraft to the right with ailerons and notices the nose yawing left. The most appropriate corrective action is to:

  1. Apply back pressure on the elevator
  2. Retract the flaps
  3. Apply right rudder Correct answer.
  4. Apply left rudder

Explanation

The left yaw is adverse yaw, which opposes the intended right roll, so coordinated flight requires rudder into the turn, that is right rudder. Failing to correct it produces a slipping flight path and increased drag.

Question 19Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

A stabilator differs from a conventional horizontal stabiliser with a separate elevator because a stabilator:

  1. Uses the whole horizontal surface as a movable pitch control Correct answer.
  2. Is mounted vertically on the fin
  3. Only operates when the flaps are extended
  4. Is fixed and cannot move

Explanation

A stabilator is an all-moving horizontal tail in which the entire surface pivots to change pitch, giving strong pitch authority. Because the whole surface moves, an anti-balance tab or geared tab is often fitted to provide acceptable control feel.

Question 20Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

A variable-incidence horizontal stabiliser is used on some aircraft so that:

  1. The rudder can act as a speed brake
  2. The aircraft can be trimmed in yaw
  3. The aircraft can be trimmed in pitch without holding elevator deflection Correct answer.
  4. The wing angle of attack can be changed in flight

Explanation

Changing the incidence of the whole stabiliser alters the tail load directly, so the aircraft can be trimmed for different speeds and flap settings without a permanent elevator deflection. This reduces drag and pilot workload compared with elevator-only trim.

Question 21Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

A mass balance weight ahead of a control surface hinge is fitted in order to:

  1. Reduce the stick force in a steady turn
  2. Increase the effectiveness of the trim tab
  3. Prevent the control surface from being locked by the wind on the ground
  4. Move the surface centre of gravity to or ahead of the hinge, reducing flutter tendency Correct answer.

Explanation

Flutter occurs when aerodynamic, elastic and inertia forces couple; bringing the surface centre of gravity forward to the hinge line removes the inertia driving force from the coupling. The weight therefore improves flutter resistance rather than control feel.

Question 22Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

In a semi-monocoque fuselage, the skin is stiffened by stringers mainly to:

  1. Prevent the skin from buckling under compression and shear Correct answer.
  2. Increase the weight of the structure
  3. Allow the fuselage to bend freely without load
  4. Provide mounting points for the seats

Explanation

Thin skin has low buckling strength in compression and shear, so longitudinal stringers divide it into smaller panels and raise the buckling stress. The stiffened skin can then carry its share of the bending and shear loads.

Question 23Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

Which statement about the wing torsion box is correct?

  1. It is formed by the front and rear spars together with the upper and lower skin Correct answer.
  2. It is the space between the wing tip and the aileron
  3. It is a non-structural fairing over the flap tracks
  4. It consists only of the trailing-edge flaps

Explanation

The torsion box is the closed cell bounded by the front and rear spars and the upper and lower wing skins. Its closed section is very efficient at resisting the torsional loads produced by the wing's aerodynamic centre being ahead of its flexural axis.

Question 24Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

An aircraft is fitted with a T-tail. Compared with a conventional tail, one consequence is that:

  1. The elevator becomes unnecessary
  2. The horizontal stabiliser may be affected by wing wake at high angles of attack Correct answer.
  3. The horizontal stabiliser is always immersed in propeller slipstream
  4. The fin carries no loads

Explanation

With the horizontal surface at the top of the fin, it can enter the wing wake or be shielded at high angles of attack, which may reduce elevator effectiveness and cause a deep-stall tendency. The fin must also be stronger because it carries the tail loads at its tip.

Question 25Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

Differential aileron travel is incorporated in a wing to:

  1. Make both ailerons deflect by the same amount
  2. Allow the ailerons to act as flaps
  3. Prevent the ailerons from moving at high speed
  4. Increase the up-going aileron deflection relative to the down-going one, reducing adverse yaw Correct answer.

Explanation

By rigging the up-going aileron to deflect more than the down-going one, the extra drag on the rising wing is reduced and the lift increase on the descending wing is limited, so adverse yaw is diminished. The roll response becomes better coordinated.

Question 26Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

In a typical light aeroplane, the secondary flight controls include:

  1. Ailerons, elevators and trim tabs
  2. Elevators, rudder and flaps
  3. Flaps, trim tabs and spoilers Correct answer.
  4. Ailerons, elevators and rudder

Explanation

Secondary flight controls are those that modify the aerodynamic characteristics of the aircraft but are not used as the primary means of controlling the flight path. They include flaps, trim tabs, spoilers and leading-edge devices. Primary controls are the ailerons, elevator and rudder.

Question 27Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

A wing is constructed with two main spars, ribs and a stressed skin. The primary function of the ribs is to:

  1. Act as a torsion box to resist twisting of the wing
  2. Carry the bending loads along the span of the wing
  3. Provide a mounting point for the engine and landing gear
  4. Maintain the aerofoil shape and transfer loads between the skin and the spars Correct answer.

Explanation

Ribs are transverse members that give the wing its aerofoil profile and support the skin, transmitting aerodynamic and inertial loads to the spars. They also help maintain the stability of the skin in compression. Bending loads are primarily carried by the spars, while the torsion box is formed by the spars and skin.

Question 28Airframe structures: fuselage, wings, empennage, primary and secondary flight controls

An aircraft has a wing with a high aspect ratio and a semi-monocoque fuselage. During a gust encounter, the wing bends upwards. The bending moment at the wing root is primarily resisted by:

  1. The upper and lower wing skins acting with the spars Correct answer.
  2. The ribs alone
  3. The fuselage frames alone
  4. The stringers in the fuselage

Explanation

In a semi-monocoque wing, the bending moment is carried by the spar caps and the wing skins, which act together as a beam. The upper skin is in compression and the lower skin in tension during upward bending. Ribs and fuselage frames do not carry the primary wing bending loads.

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

On a transport-category aircraft hydraulic system, what is the primary purpose of the reservoir pressurisation?

  1. To increase the output pressure of the engine-driven pump
  2. To cool the fluid by expanding it into the reservoir
  3. To prevent pump cavitation at altitude and keep fluid supplied to the pump inlet Correct answer.
  4. To automatically replenish the system after a leak

Explanation

Reservoir pressurisation, usually by bleed air or a hydraulic accumulator, maintains a positive head at the pump inlet. This suppresses cavitation and ensures a continuous fluid supply when ambient pressure falls with altitude. It does not raise system operating pressure, which is set by the pump and relief valve.

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

An engine-driven hydraulic pump is described as a variable-displacement, pressure-compensated type. What does the compensator do when system pressure reaches the set value?

  1. It opens the reservoir return and dumps all pump output
  2. It increases pump displacement to raise pressure further
  3. It destrokes the pump so displacement falls to match demand Correct answer.
  4. It stops the pump drive shaft from rotating

Explanation

A pressure compensator senses outlet pressure and moves the swashplate or yoke to reduce stroke as the set pressure is approached. Displacement therefore falls to whatever is needed to hold pressure, wasting little energy. The drive shaft keeps turning and the pump does not dump full flow overboard.

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

What is the function of a hydraulic system accumulator?

  1. To convert hydraulic pressure into mechanical rotary motion
  2. To measure and display system pressure in the cockpit
  3. To filter particulate contamination from the return line
  4. To store pressurised fluid for peak demand and damp pressure surges Correct answer.

Explanation

An accumulator contains a gas charge separated from the hydraulic fluid by a bladder, diaphragm or piston. It stores energy for short peak demands, smooths pressure pulses and can supply limited emergency operation. It is not a filter, actuator or gauge.

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

Before servicing a hydraulic system fitted with a bladder-type accumulator, what precaution is essential?

  1. Relieving hydraulic pressure so the fluid side is depressurised Correct answer.
  2. Heating the fluid to reduce its viscosity
  3. Overfilling the reservoir to displace trapped air
  4. Fully discharging the gas precharge to atmosphere

Explanation

The gas precharge keeps the fluid side under pressure even with the pumps off. Hydraulic pressure must be relieved before any component is opened, or fluid will be ejected under pressure. Venting the gas charge is a separate step only needed when the accumulator itself is removed.

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

In a hydraulic system, what is the purpose of the pressure relief valve?

  1. To limit maximum system pressure by returning excess flow to the reservoir Correct answer.
  2. To prevent reverse flow from the actuators back to the pump
  3. To maintain a constant flow rate to the actuators regardless of load
  4. To isolate a failed branch of the system automatically

Explanation

The relief valve opens at a preset pressure and bypasses excess fluid to return, protecting components from overpressure. It is a safety device and normally stays closed in cruise. Flow regulation and reverse-flow prevention are duties of other valves.

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

A hydraulic system uses a selector valve to extend a double-acting actuator. What happens to the fluid on the retract side of the piston?

  1. It is trapped and compressed against the piston
  2. It returns to the reservoir through the return line Correct answer.
  3. It is pumped back into the pressure line to assist the pump
  4. It is vented overboard through a drain mast

Explanation

A selector valve directs pressure to one side of the piston while connecting the other side to return. The displaced fluid flows back to the reservoir, completing the circuit. Fluid is not vented overboard, and the retract side is not left trapped.

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

What is the primary role of a hydraulic fuse in an aircraft system?

  1. To limit the rate of pressure rise during pump start
  2. To melt at a set temperature and release pressure
  3. To isolate a line that has lost fluid, limiting leakage after a downstream failure Correct answer.
  4. To filter fine contamination from the pressure line

Explanation

A hydraulic fuse senses excessive flow, as occurs when a downstream line ruptures, and closes to isolate the damaged section. This conserves fluid and preserves pressure for the remaining services. It does not respond to temperature, contamination or pressure rise rate.

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

An aircraft has a hydraulic system with a priority valve supplying the flight controls and the landing gear. During gear extension the pressure begins to fall. How does the priority valve respond?

  1. It reduces flow to the flight controls so the gear receives full flow
  2. It restricts flow to the landing gear to protect the flight controls Correct answer.
  3. It opens the relief valve to dump pressure overboard
  4. It shuts off both services until pressure recovers

Explanation

A priority valve gives the essential service, here the flight controls, first call on available flow. If pressure drops, flow to the lower-priority gear circuit is reduced or cut off. This preserves control authority at the expense of slower gear operation.

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

A hydraulic pump produces 10 litres per minute at 200 bar. Ignoring losses, what hydraulic power is being delivered?

  1. About 200 kW
  2. About 0.33 kW
  3. About 3.3 kW Correct answer.
  4. About 33 kW

Explanation

Hydraulic power equals pressure multiplied by flow rate. Using SI units, 200 bar is 20 MPa and 10 L/min is 1.67 x 10^-4 m3/s, giving about 3.3 kW. This confirms that pressure alone does not define power without the flow term.

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

Why are hydraulic systems on large aircraft commonly duplicated into two or more independent circuits?

  1. To simplify the cockpit indication requirements
  2. To reduce the total quantity of fluid carried
  3. To allow the use of smaller diameter tubing throughout
  4. To provide redundancy so a single failure does not remove all hydraulic power Correct answer.

Explanation

Multiple independent systems, each with its own reservoir and pump source, ensure that a leak or pump failure in one circuit leaves others available. Critical services are distributed across the systems. This redundancy adds weight and complexity but greatly improves safety.

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

What does a hydraulic system pressure gauge in the cockpit actually indicate?

  1. The position of the actuator pistons
  2. The pressure at the pump outlet or manifold, sensed by a transducer Correct answer.
  3. The temperature of the fluid in the return line
  4. The quantity of fluid remaining in the reservoir

Explanation

A pressure gauge displays the pressure sensed at a chosen point, usually the pump outlet or system manifold, via a pressure transducer and indicator. Quantity, temperature and actuator position have their own separate indications. The gauge does not measure flow.

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

During cruise, the hydraulic system low-pressure warning illuminates briefly and then extinguishes. Which action is most appropriate?

  1. Ignore it because transient warnings are always spurious
  2. Note it and monitor the system indications, referring to the checklist if it recurs Correct answer.
  3. Immediately shut down the associated pump
  4. Open the reservoir bleed to restore pressure

Explanation

A brief transient may be caused by pump changeover or a momentary demand peak, but it must not be dismissed. The crew should monitor pressure, quantity and temperature and consult the checklist if the warning repeats. Immediate shutdown or bleeding is not justified by a single transient.

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

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

  1. To permit flow in one direction only and prevent reverse flow Correct answer.
  2. To sequence the operation of two actuators
  3. To relieve excess pressure to the return line
  4. To regulate flow to a constant value regardless of pressure

Explanation

A check valve is a one-way valve that allows free flow in the intended direction and blocks reverse flow. It protects pumps and components from backflow and holds pressure in selected lines. Flow regulation, relief and sequencing are separate functions.

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

A hydraulic reservoir is fitted with a vent line to atmosphere. What is the main reason for this on a low-pressure, unpressurised system?

  1. To allow the reservoir to breathe as fluid level changes and prevent a vacuum or overpressure Correct answer.
  2. To cool the fluid by forced convection
  3. To allow fluid to escape if the reservoir is overfilled
  4. To supply air to the hydraulic pump for priming

Explanation

As actuators move, fluid leaves and returns to the reservoir, changing the level and the air volume above it. The vent equalises pressure with the atmosphere so the pump inlet is not starved and the reservoir is not stressed. A separate overflow drain handles overfilling.

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

In a closed-centre hydraulic system, what is the state of the selector valve when no actuation is commanded?

  1. The actuator is free to move under external load
  2. Both actuator ports are blocked and pump flow is near zero Correct answer.
  3. Pressure is continuously bypassed to the reservoir
  4. Both actuator ports are connected to return

Explanation

Closed-centre valves block the actuator ports in the neutral position, so no flow passes and the pump destrokes to hold pressure with minimal energy use. Open-centre systems instead bypass flow to return when idle. Blocking the ports also locks the actuator in position.

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

What is the main consequence of air entering a hydraulic system?

  1. Increased fluid viscosity and slower actuation
  2. Higher system pressure because air is compressible
  3. Spongy actuation, cavitation and possible pump damage Correct answer.
  4. Automatic purging of the system through the reservoir

Explanation

Entrained air is compressible, so actuator response becomes spongy and delayed. As it passes through the pump it can cause cavitation, noise, vibration and erosion damage. Air must be removed by bleeding and the source of ingress found.

Question 45Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system indications

A hydraulic fluid is described as having a high viscosity index. What does this mean?

  1. It has a high flash point
  2. Its viscosity changes relatively little with temperature Correct answer.
  3. It has a high resistance to contamination
  4. Its viscosity is high at all temperatures

Explanation

The viscosity index expresses how much viscosity changes with temperature. A high index means the fluid's viscosity stays comparatively stable from cold start to operating temperature. It says nothing about absolute viscosity, contamination resistance or flash point.

Question 46Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system indications

A hydraulic actuator moves slowly and erratically while system pressure remains normal. Which cause is most consistent with these symptoms?

  1. A blocked return filter causing high back pressure
  2. A pressure transducer with a calibration error
  3. A failed pressure relief valve stuck open
  4. Internal leakage past the actuator piston seals Correct answer.

Explanation

Normal pressure at the manifold with slow, erratic movement suggests flow is bypassing the piston internally rather than reaching the load. Worn or damaged piston seals allow fluid to leak across the actuator, reducing effective force and speed. A relief valve stuck open would show low pressure instead.

Question 47Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system indications

Why is a hydraulic system usually fitted with both a main system relief valve and a thermal relief valve?

  1. The main relief protects the actuators while the thermal relief protects the reservoir only
  2. The main relief protects against pump overpressure while the thermal relief relieves fluid expansion when the system is isolated Correct answer.
  3. The main relief handles return-line pressure while the thermal relief protects the pump
  4. The thermal relief replaces the main relief during cold weather

Explanation

The main relief valve limits pressure generated by the pump during operation. When the system is shut down and isolated, trapped fluid can warm and expand, so a thermal relief valve releases the excess and prevents line or component damage. The two devices protect against different threats.

Question 48Hydraulic systems: reservoirs, pumps, accumulators, valves, actuators and system indications

What is the function of a hydraulic flow-control valve in a system supplying an actuator that must move at a steady rate?

  1. To limit the maximum pressure in the actuator line
  2. To maintain a constant flow to the actuator despite pressure variations Correct answer.
  3. To store fluid for peak demand
  4. To prevent reverse flow when the actuator is parked

Explanation

A flow-control valve regulates the volume of fluid passing per unit time, so actuator speed stays steady even as load pressure changes. Pressure limiting, reverse-flow prevention and energy storage belong to relief valves, check valves and accumulators respectively.

Question 49Pneumatic and air-conditioning/pressurisation systems

On a typical transport-category aircraft, the cabin pressurisation system is designed primarily to do which of the following?

  1. Maintain cabin altitude within physiologically acceptable limits at high aircraft altitude Correct answer.
  2. Provide ram airflow for avionics cooling during ground operations
  3. Supply heated air to the wing leading edges for anti-icing
  4. Regulate fuel tank inerting pressure during climb and descent

Explanation

Pressurisation exists to keep the cabin at a breathable equivalent altitude while the aircraft operates far higher, typically holding cabin altitude below about 8000 ft. Structural differential pressure limits and occupant comfort both constrain the schedule. Heating, anti-icing and tank inerting are separate functions served by other systems.

Question 50Pneumatic and air-conditioning/pressurisation systems

Bleed air taken from a low-pressure engine compressor stage is normally supplemented by high-pressure stage air because:

  1. Low-stage bleed pressure falls below the required delivery pressure at low engine thrust settings Correct answer.
  2. High-stage air is cooler and therefore needs less precooling before use
  3. High-stage bleed is used only when the APU is unavailable
  4. Low-stage bleed contains more oil contamination than high-stage bleed

Explanation

At low power settings the low-pressure port cannot deliver the pressure needed by the pneumatic system, so a pressure-regulating and shut-off valve switches to the high-stage port. At high power the low-stage port is used to limit bleed temperature and engine performance penalties. The switch is driven by pressure availability, not by oil contamination or APU status.