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DGCA Technical General · 116 questions

Aircraft Systems: DGCA Technical General Questions and Answers

116 practice questions on Aircraft Systems with answers and explanations, plus the key concepts and formulas, from the TrueHeading question bank.

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About this topic

Use this page to revise Aircraft Systems for the DGCA Technical General paper. Below are the key ideas first, then 12 practice questions with answers and explanations, picked from the 116 questions in the TrueHeading bank for this topic.

In short: Pressure applied to a confined fluid is transmitted equally in all directions.

Open the full set in the student zone to answer every question, track your accuracy and take timed mock tests.

Key concepts: Aircraft Systems

8 ideas to know cold.

Hydraulics: Pascal’s law?

Pressure applied to a confined fluid is transmitted equally in all directions.

P=FAP=\frac{F}{A}
  • Engine-driven or electric pumps, reservoir, accumulator, filters
  • Used for gear, flaps, brakes and flight controls

Pressurisation basics?

Bleed air is conditioned, then the outflow valve controls cabin pressure.

  • Cabin altitude is held at or below about 8000 ft
  • Safety valves protect against over- and negative pressure
  • Cabin altitude warning at about 10 000 ft; oxygen masks drop at about 14 000 ft

Aircraft electrical power?

Generators or alternators supply AC; transformer-rectifier units convert to DC.

  • Typical airliner: 115 V AC, 400 Hz and 28 V DC
  • Battery for starting and emergency
  • Constant-speed drive keeps frequency fixed

Ice protection?

Two approaches:

  • De-icing: removes ice, for example pneumatic boots
  • Anti-icing: prevents ice forming, using bleed air or electric heating
  • Fluid systems (TKS) use glycol

Oxygen systems?

Crew: gaseous. Passengers: chemical generators or gaseous, released when cabin altitude passes about 14 000 ft.

  • Oxygen and oil or grease never mix
  • Know where the generator or cylinder is

Describe the cabin pressurisation system.

Engine bleed air supplies the cabin; the outflow valve regulates the pressure; relief valves protect the structure.

Δp=pcabin−pambient\Delta p=p_{cabin}-p_{ambient}
  • Typical cabin altitude about 8 000 ft at cruise
  • Differential pressure max about 8–9 psi
  • Cabin altitude warning at 10 000 ft
  • Masks drop at 14 000 ft

What are the main hydraulic system components?

Reservoir, pump, accumulator, filter, relief valve, selector valve, actuator, fuses.

F=p×AF=p\times A
  • Fluid: incompressible, e.g. Skydrol (phosphate ester)
  • Pressure typically 3 000 psi
  • Force = pressure × area

Electrical system basics?

Generators (AC, 115 V/400 Hz), TRUs (AC→DC 28 V), batteries, buses, circuit breakers, RAT in emergency.

P=V×IP=V\times I
  • Power = V × I
  • Constant-speed drive keeps frequency steady
  • APU and external power on the ground

Practice questions: Aircraft Systems

Tap “Show answer” after you have tried each one.

Q1A hydraulic actuator operates at 1500 psi and its piston area is 5 in². The force produced is:

  1. 8625 lb
  2. 12000 lb
  3. 7500 lb
  4. 9375 lb
Show answer

Answer: C. 7500 lb

Force = pressure × area = 1500 × 5 = 7500 lb.

Q2A hydraulic actuator operates at 4000 psi and its piston area is 2 in². The force produced is:

  1. 10000 lb
  2. 7200 lb
  3. 9200 lb
  4. 8000 lb
Show answer

Answer: D. 8000 lb

Force = pressure × area = 4000 × 2 = 8000 lb.

Q3A 28 V DC circuit draws 8 A. The power consumed is:

  1. 168 W
  2. 246 W
  3. 224 W
  4. 190 W
Show answer

Answer: C. 224 W

P = V × I = 28 × 8 = 224 W.

Q4A 12 V DC circuit draws 10 A. The power consumed is:

  1. 192 W
  2. 72 W
  3. 102 W
  4. 120 W
Show answer

Answer: D. 120 W

P = V × I = 12 × 10 = 120 W.

Q5A 28 V supply drives a current of 4 A through a resistor. The resistance is:

  1. 7.0 Ω
  2. 9.8 Ω
  3. 8.0 Ω
  4. 7.7 Ω
Show answer

Answer: A. 7.0 Ω

R = V ÷ I = 28 ÷ 4 = 7.0 Ω.

Q68000 kg of fuel with a specific gravity of 0.85 occupies a volume of:

  1. 8470 litres
  2. 10350 litres
  3. 9410 litres
  4. 15060 litres
Show answer

Answer: C. 9410 litres

Volume = mass ÷ SG = 8000 ÷ 0.85 = 9412 litres.

Q7ISA pressure at 39 000 ft ≈ 197 hPa and at a cabin altitude of 8 000 ft ≈ 753 hPa. The differential pressure is approximately (psi):

  1. 8.1 psi
  2. 10.6 psi
  3. 4.0 psi
  4. 16.1 psi
Show answer

Answer: A. 8.1 psi

Differential = cabin pressure − ambient pressure; 1 psi = 68.95 hPa.

Q8A hydraulic actuator piston has an area of 1.5 in² and the system pressure is 3000 psi. The force produced is:

  1. 2 250 lbf
  2. 9 000 lbf
  3. 2 000 lbf
  4. 4 500 lbf
Show answer

Answer: D. 4 500 lbf

Force = pressure × area.

Q9An electrical load draws 10 A from a 115 V supply. The power consumed is:

  1. 115 W
  2. 1 150 W
  3. 2 300 W
  4. 11 500 W
Show answer

Answer: B. 1 150 W

P = V × I.

Q10A hydraulic priority valve:

  1. stops all hydraulic flow
  2. dumps fluid overboard
  3. ensures essential services get pressure first when pressure is low
  4. increases pressure to all systems
Show answer

Answer: C. ensures essential services get pressure first when pressure is low

Non-essential systems are isolated.

Q11Chemical oxygen generators for passengers produce oxygen for:

  1. about 12 to 22 minutes
  2. about 2 minutes
  3. about 1 minute
  4. about 2 hours
Show answer

Answer: A. about 12 to 22 minutes

Typically at least 12 minutes, enough to descend to a safe altitude.

Q12An inverter:

  1. converts DC to AC
  2. converts AC to DC
  3. reduces the current only
  4. increases the voltage
Show answer

Answer: A. converts DC to AC

It supplies AC from batteries in an emergency.

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More DGCA Technical General topics

Aerodynamics & Performance181 QFlight Controls & Stability38 QAirframe & Structures25 QPowerplant79 QPropellers32 QPitot Statics35 QBarometric Altimeters61 QRadio Altimeters37 QVertical Speed Indicators (VSI)32 QAirspeed Indicators24 QAirspeeds41 QMach55 QGyroscope52 QAttitude Indicators20 QTurn and Slip50 QINS, IRS and FMS32 QEFIS24 QAutoflight23 QFlight Director21 QEICAS / ECAM24 QEngine Instruments29 QTemperature Indicators34 QFuel Systems35 QCompass54 QWarning & Recording Systems33 QTCAS39 Q
All DGCA questionsCPL exam syllabusHow to prepareTechnical General formulas

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