DGCA Technical General: Pneumatics & Pressurisation Questions
134 exam-style Pneumatics & Pressurisation 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.
- Q1
The purpose of a ditching control valve is
- A Close the outflow valves
- B Open outflow valves
- C To allow rapid depressurisation
- D To dump the toilet water after landing
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Correct answer: A. Close the outflow valves
Operating the ditching control closes the outflow valves, along with other openings below the expected waterline, to seal the pressure hull against water entry and preserve buoyancy after alighting on water. It closes rather than opens the valves, and has nothing to do with depressurisation rate or waste systems.
- Q2
In a vapour cycle cooling system what is the purpose of the condenser
- A To remove moisture from the air by centrifugal action
- B To convert the refrigerant from a liquid to a gas
- C To convert the refrigerant from a gas to a liquid
- D To raise the pressure of the gas to allow efficient cooling
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Correct answer: C. To convert the refrigerant from a gas to a liquid
After the compressor raises the pressure of the hot refrigerant vapour, the condenser rejects that heat to the outside air, causing the refrigerant to change from a high-pressure gas back into a liquid ready to pass through the expansion valve. It is the evaporator that does the reverse, turning liquid into gas.
- Q3
Why are some aircraft pressurisation systems to referred to as bootstrap systems?
- ABecause they are air cycle machines.
- BBecause they are vapour cycle machines.
- CThey are activated by pull cords.
- DThey employ refrigerants.
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Correct answer: A. Because they are air cycle machines.
This Explanation is Coming Soon
- Q4
If cabin pressure is decreasing, the cabin VSI will indicate
- A Zero
- B Climb
- C Descent
- D Reducing pressure
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Correct answer: B. Climb
A cabin VSI reads rate of change of cabin altitude, so a falling cabin pressure means the cabin altitude is rising and the instrument indicates a climb. Decreasing pressure is equivalent to gaining altitude.
- Q5
The excess cabin altitude alerting system must operate to warn the crew at8,000ft
- A 8,000ft
- B 10,000ft
- C 13,000ft
- D14,000ft
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Correct answer: B. 10,000ft
The cabin altitude warning system must alert the crew when the cabin altitude reaches about 10,000 ft, the level at which supplemental oxygen becomes necessary, prompting them to act before hypoxia sets in.
- Q6
The ditching control valve?
- AOpens the outflow and inward relief valves.
- BCloses the outflow valves.
- CCloses the mass flow controller.
- DOpens the outflow valves.
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Correct answer: B. Closes the outflow valves.
This Explanation is Coming Soon
- Q7
In an air cycle air conditioning system what is the function of the ground-cooling fan.
- A To re-circulate air through the mix manifold
- B To draw cooling air over the turbine
- C To blow air into the compressor
- D To draw cooling air over the heat exchangers
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Correct answer: D. To draw cooling air over the heat exchangers
On the ground there is no ram airflow to carry away the heat rejected by the air-conditioning heat exchangers, so a ground-cooling fan is provided to draw cooling air over the heat exchangers and maintain their effectiveness while stationary.
- Q8
The heat exchanger in a bootstrap system?
- ACools both the bled air and the compressor outlet air.
- Bheat the incoming air.
- CCools the incoming air.
- DExtracts heat from the exhaust air before it is discharged overboard.
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Correct answer: A. Cools both the bled air and the compressor outlet air.
This Explanation is Coming Soon
- Q9
502.When air is pressurized by an engine driven compressor, it is also:
- ACooled
- B Heated
- CMoisturized
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Correct answer: B. Heated
Compressing air does work on it, and by the gas laws the pressure rise is accompanied by a large temperature rise, which is why engine-driven compressor or bleed air must be cooled before it is used in the cabin.
- Q10
If an aircraft maximum operating altitude is limited by the pressure cabin, this limit is due to
- AThe maximum positive pressure differential at maximum operating ceiling
- B The maximum positive pressure differential at maximum cabin altitude
- C The maximum number of pressurisation cycles
- D The maximum zero fuel mass at maximum pressure altitude
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Correct answer: B. The maximum positive pressure differential at maximum cabin altitude
When the maximum altitude is set by the pressure cabin, the limit is the maximum positive pressure differential the fuselage structure can withstand: as the aircraft climbs and the cabin is held at its target altitude, the difference between cabin and outside pressure grows until the structural differential limit is reached.
- Q11
If the pressure controller malfunctions during the cruise and the outflow valve opens what happens to: i) Cabin ROC ii) Cabin Alt iii) Differential pressure
- Ai) Increase ii) Decrease iii) Decrease
- B i) Decrease ii) Increase iii) Decrease
- C i) Increase ii) Increase iii) Decrease
- D i) Increase ii) Increase iii) Increase
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Correct answer: C. i) Increase ii) Increase iii) Decrease
If the controller fails and the outflow valve opens, air escapes faster than it is supplied, so the cabin pressure falls: the cabin rate of climb increases, the cabin altitude increases, and because the cabin pressure drops toward ambient the differential pressure decreases.
- Q12
If an aircraft suffers decompression what happens to the indications on a cabin VSI, cabin altimeter and differential pressure gauge
- A VSI up, altimeter up, differential pressure gauge down
- B VSI, altimeter, differential pressure gauge all unchanged
- C VSI down, altimeter up, differential pressure gauge down
- D VSI up, altimeter down, differential pressure gauge down
Show answer
Correct answer: A. VSI up, altimeter up, differential pressure gauge down
On decompression the cabin pressure falls toward ambient, so the cabin altitude rises: the cabin altimeter reads up and the cabin VSI shows a rapid climb (up), while the reduced difference between cabin and outside pressure makes the differential pressure gauge read down.
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