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Module 13 EASA Part 1 > 13.11.2 Air Conditioning > Flashcards

13.11.2 Air Conditioning Flashcards

1
Q

What are the four sources of air supplies for the air conditioning system on an aircraft?

A

Gas turbine compressors

Engine driven blowers

APU compressors

Ambient ram air inlets

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2
Q

What is the first stage of cooling in an air conditioning system?

A

Primary heat exchanger

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3
Q

What is the alternative name for the air cycle machine?

A

Cold air unit

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4
Q

How can the mix valve be controlled in the event of failure of the temperature regulator?

A

Manually using the temperature selector switch

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5
Q

What causes a signal to drive the mix valve to change positions when the temperature selector switch is in the ‘auto’ position?

A

Control bridge circuit with reference resistance from switch on one arm and cabin temperature sensor on the other arm

When unbalanced, a signal is developed

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6
Q

What is the purpose of the anticipation and limit sensors in the ducting to the cabin?

A

Modulate any rapid changes as a result of unbalanced bridge

Prevents sudden blasts of hot or cold air

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7
Q

What happens when the heat in the duct reaches 90°C?

A

Moves the mix valve to fully cold

Duct overheat light illuminates

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8
Q

How can the system be returned to normal following a temperature of 90°C?

A

Pushing the reset button

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9
Q

Under what condition does the other thermal switch protect the air conditioning duct from overheating?

A

Should control electrical power be lost

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10
Q

In the air conditioning system, what does the 120°C switch operate?

A

Pack valve closing

Illuminating the pack trip off light

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11
Q

Under what other conditions, other than the 120°C overheat switch being activated, will the pack valve close due to overheat?

A

If the air cycle machine compressor discharge overheat switch is actuated

or

If the air cycle machine turbine inlet overheat switch is actuated

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12
Q

At what temperature will the air conditioning pack deliver air to the different aircraft zones?

A

Pack output temperature will be to the lowest zone temperature selected

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13
Q

On long haul flights, what is the relative humidity kept at using humidifiers?

A

30%

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14
Q

How does a humidifier operate?

A

Potable water jet impinges at right angles on the high pressure air jet

Water becomes atomised

Air becomes uniformly saturated

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15
Q

Why is the recirculating air entering the mixing chamber made to swirl?

A

Ensures that the recirculated air and the fresh conditioned air are thoroughly mixed

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16
Q

In the recirculation fan, what are the relative quantities of fresh air to recirculated cabin air?

A

60% fresh

40% recirculated cabin air

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17
Q

What are the symptoms of ozone exposure?

A

Chest pain

Coughing

Shortness of breath

Fatigue

Headaches

Nasal congestion

Eye irritation

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18
Q

How does an ozone converter work?

A

Separates ozone from the air and by catalytic action of the substance contained within the converter, converts ozone to oxygen

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19
Q

What type of noble metal is used in a ozone converter?

A

Palladium

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20
Q

What is the principle of vapour cycle cooling?

A

Latent heat

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21
Q

What are the basic components of a basic vapour cycle cooling system?

A

Receiver dryer

Thermostatic expansion valve

Evaporator

Compressor

Condenser

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22
Q

How is the amount of refrigerant put into a system determined?

A

By weight rather than volume

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23
Q

How is refrigerant normally put into the system?

A

In its vapour form after the system has been evacuated and is still under vacuum

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24
Q

What must be done when opening the refrigerant system?

A

All the refrigerant must be recovered using special equipment

Not permitted to release the refrigerant into the atmosphere

25
Q

What must be done if a refrigeration system has been opened?

A

It must be evacuated before it is recharged

26
Q

What properties must refrigerants used in aircraft installations have?

A

Non–flammable

Non–explosive

Non–toxic, both in pure state and when mixed in air

The refrigerant must not react unfavourably with lubricating oils used within the system

Ideally the lubricating oil should be miscible with the refrigerant

Non–corrosive

27
Q

What refrigerant are aircraft systems being modified to use or designed for?

A

Refrigerant R–134a

28
Q

What are the three principles of air cycle cooling?

A

Surface heat exchange

Expansion

Energy conversion

29
Q

Where does the fuel in combustion heaters come from?

A

Aircraft fuel tanks

30
Q

What is the medium that is heated in a combustion heater?

A

Ram air

31
Q

Why is ram air kept at a positive pressure?

A

To prevent noxious gases from entering the cabin

32
Q

What is the purpose of the ‘whirling’ flame produced in the combustion chamber?

A

Ensures even burning of the fuel and heating of the chamber walls

33
Q

In a combustion heater, what is the purpose of the limit switch?

A

First line of defence against overheat

Closes fuel valve, opens it again once the overheat condition is removed

34
Q

In a combustion heater, what is the purpose of the overheat switch and how does it differ from the limit switch?

A

If the temperature continues to rise past that which would normally operate the limit switch

Shut the combustion heater down and cannot be restarted in flight

35
Q

What continues to operate in a combustion heater, even though the fuel valve is closed?

A

Spark plug and combustion blower

36
Q

What does CAP 747 GR11 require about combustion heaters?

A

Intervals not exceeding 500 operating hours, or 2 years, whichever is sooner, combustion heaters and their exhaust systems must be completely dismantled and inspected

37
Q

Which valve must open to allow engine bleed air into the air conditioning system?

A

Electro–pneumatic pack valves

38
Q

Which valves allow hot bleed air to bypass the cold air unit?

A

Mix valve

1.7°C valve

39
Q

What is the name of the system which allows passengers to be individually cooled?

A

Gasper outlets

40
Q

How is cooling achieved through the heat exchangers when the aircraft is on the ground?

A

A turbo fan induces air to flow across the heat exchangers

41
Q

How is the temperature in the duct between the compressor and the secondary heat exchanger controlled?

A

Ram air temperature sensor

42
Q

State the two ways the turbine of the ACM achieves cooling?

A

Pressure drop

Heat energy converted to mechanical energy

43
Q

How is the water extractor prevented from freezing?

A

Temp sensor control 35°F (1.7°C) valve

Valve will allow by–pass warm air past the ACM into the inlet of the water separator

Prevents moisture freezing

44
Q

Which three sensors would trip the pack valve?

A

ACM compressor discharge overheat switch

ACM turbine inlet overheat switch

120°C thermal switch

45
Q

What would cause the mix valve to motor to fully cold?

A

90°C duct overheat thermal switch

46
Q

What might cause the compressor discharge overheat sensor to operate?

A

A problem with the ram air inlet which has an effect on the primary heat exchanger

47
Q

What is the purpose of a three wheel air cycle machine?

A

Incorporates a fan which is used to induce airflow across the heat exchangers by its own action

48
Q

What two things would happen if the water extractor became blocked with ice?

A

Indicator piston moves from the white area into the red coloured area of the indicator cap

Safety relief valve operates to ensure the flow of air into the cabin

49
Q

In a displacement blower system, which two components control the amount of air in the system?

A

Excess air is spilled off by opening or closing a spill valve

Mass flow controller controls the spill valve

50
Q

What is the purpose of the choke valve in the displacement blower system?

A

Restricts the flow, thus producing a pressure rise to increase the air temperature

51
Q

What is latent heat?

A

Quantity of heat which causes a change in state of a substance without changing the temperature

52
Q

Which components control the amount of liquid refrigerant entering the evaporator?

A

Thermostatic expansion valve

Temperature bulb

53
Q

What state is the refrigerant in when it enters the evaporator?

A

Mostly in liquid form

54
Q

Besides driving the refrigerant around the system, what other function does the compressor provide?

A

Lowers the pressure in the evaporator

Supplies refrigerant to the condenser at a pressure and temperature at which it can be easily condensed back into liquid

Raises the pressure of the refrigerant

55
Q

What state is the refrigerant in when it enters the condenser?

A

Hot gas

56
Q

What is the function of the receiver dryer?

A

Reservoir of the system

57
Q

Within the manifold set, what are the colours of the hoses for the high side, the low side and the centre hose?

A

High side – red

Low side – blue

Centre hose – yellow

58
Q

In a combustion heater, what would happen if the normal thermostat in the system failed?

A

There is a limit switch

Closes fuel valve until overheat condition is corrected

59
Q

Why does the low side hose indicate a pressure below that of atmosphere?

A

It is the vacuum side

Module 13 EASA Part 1 (20 decks)

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