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DGCA Technical General: Hydraulics Questions

162 exam-style Hydraulics questions for the DGCA Technical Generalpaper (CPL & ATPL). The first 12 are free below with answers and explanations — sign up free to practise all of them with progress tracking.

  1. Q1

    Modern aircraft hydraulic systems use?

    • AMineral based fluid.
    • BSynthetic fluids.
    • CAlcohol based fluids.
    • DVegetable based fluids.
    Show answer

    Correct answer: B. Synthetic fluids.

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  2. Q2

    In a modern airliner what is hydraulic fluid used

    • A Synthetic
    • B Mineral
    • C Mineral/alchohol
    • D Vegetable
    Show answer

    Correct answer: A. Synthetic

    Modern airliners use a synthetic phosphate-ester based hydraulic fluid, chosen chiefly for its fire-resistant properties compared with the flammable mineral-based fluids used in older and lighter aircraft.

  3. Q3

    What type of hydraulic fluid is used in a modern passenger jet aircraft

    • A Mineral based
    • B Phosphate ester based
    • C Vegetable based
    • D Water based
    Show answer

    Correct answer: B. Phosphate ester based

    Modern passenger jets use a phosphate-ester based synthetic hydraulic fluid because of its fire-resistant qualities, unlike the flammable mineral-based fluids found in older aircraft.

  4. Q4

    A shuttle valve is used to?

    • ASwitch from one supply to another.
    • BSwitch from one service to another .
    • COperate components in sequence.
    • DMove components backwards and forwards.
    Show answer

    Correct answer: A. Switch from one supply to another.

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  5. Q5

    Hydraulic pressure typically used in the system of large transport aircraft is

    • A2000 - 3000psi
    • B 3000 - 4000psi
    • C 1000 - 2000psi
    • D 4000 - 5000psi
    Show answer

    Correct answer: B. 3000 - 4000psi

    Large transport aircraft hydraulic systems traditionally operate at around 3000 psi, so a working range of about 3000 to 4000 psi covers these installations. This pressure gives powerful, compact actuation of flight controls, gear and brakes.

  6. Q6

    Hydraulic fluid

    • ANeeds no special treatment
    • B Is harmful to eyes and skin
    • C Is a fire hazard
    • D Is harmful to eyes and skin, and is also a fire hazard
    Show answer

    Correct answer: D. Is harmful to eyes and skin, and is also a fire hazard

    Hydraulic fluid is both a health and a fire hazard: it irritates and can damage the eyes and skin on contact, and it will burn, so it must be handled with appropriate protection and care.

  7. Q7

    One of the reasons for pressurising hydraulic reservoirs is to?

    • APrevent pump cavitation.
    • BPrevent the collection of bubbles in the reservoir.
    • CPrevent the ingress of moisture into the fluid.
    • DReduce the pressure rise necessary in the pump.
    Show answer

    Correct answer: A. Prevent pump cavitation.

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  8. Q8

    A device in a hydraulic system which acts in the same way as a diode in an electrical circuit is a:

    • A Restrictor valve
    • B Sequence valve
    • C Fuse
    • D One way check valve
    Show answer

    Correct answer: D. One way check valve

    A one-way (non-return) check valve allows hydraulic fluid to flow in one direction only and blocks flow in the reverse direction, exactly as a diode passes current one way and blocks it the other.

  9. Q9

    Hydraulic reservoirs are pressurised?

    • ABy ground crew before flight.
    • BUsing air from the air conditioning packs.
    • CUsing engine bleed air from gas turbine engines.
    • DUses a dedicated air compressor unit.
    Show answer

    Correct answer: C. Using engine bleed air from gas turbine engines.

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  10. Q10

    What is the purpose of hydraulic sequence valve?

    • ATo activate the shuttle valve
    • BTo sequence certain events
    • C To activate fire shut off valve
    Show answer

    Correct answer: B. To sequence certain events

    A sequence valve withholds fluid from one actuator until another has completed its stroke, guaranteeing that operations happen in the correct order, for example undercarriage doors opening fully before the gear extends.

  11. Q11

    A shuttle valve is used to

    • A Restrict the rate of operation of a system
    • B Select the most suitable system pressure
    • C Allow two supplies to be available to a service
    • DTo allow a constant volume pump to idle
    Show answer

    Correct answer: C. Allow two supplies to be available to a service

    A shuttle valve automatically connects a service to whichever of two supply sources is delivering pressure, typically the normal and the emergency or alternate system. This ensures the service always has a supply available even if one source fails.

  12. Q12

    A hydraulic fuse?

    • AMinimises loss of fluid in the event of a hose failure.
    • BPrevent excessive fluid flow rates when jacks become unloaded.
    • Climits the rate at which services operate.
    • DPermits gravity lowering of landing gear.
    Show answer

    Correct answer: A. Minimises loss of fluid in the event of a hose failure.

    This Explanation is Coming Soon

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More DGCA Technical General topics

DC Electrics (401)Aerofoils, Lift & Drag (301)AC Electrics (301)Gas Turbines — Principles & Construction (271)Climbing & Turning Flight (221)Flying Controls (213)Piston Engines (207)Propellers (193)Stability & Control (172)Stalling (165)Structures (160)High-Speed Flight (151)