11.04 Air Con and Cabin Pressure

Question 1

The pack valve is responsible for what?

Answer 1

The amount of air entering the cabin

Question 2

What is the sequence of the coolant through a vapour cycle machine?

Answer 2

• Expansion valve (V cold)
• Evaporator (heated by cabin air)
• Compressor (compressed)
• Condenser (cooled by ambient air)

Question 3

In an air cycle machine system, how is the supply air cooled?

Answer 3

Initially by the heat exchangers and then finally by the turbine

Question 4

If the pack valve air supply fails what would occur to the pack valve?

Answer 4

Closes under spring pressure

Question 5

What would be the effect on the ram air doors if the ACM bypass valve operates?

Answer 5

• Ram air doors operate in opposition to bypass valve position
• Bypass valve open = max heat, ram air doors close
• Bypass vale close = max cool, ram air doors open

Question 6

Briefly describe how coalescer type water separators work

Answer 6

• Water heavier than air
• Coalescer increases size of water droplets
• Swirl vanes centrifugally force air out into collector

Question 7

How many cabin pressure controllers are in a system and when will they operate?

Answer 7

• Two

- One operating and one in standby

Question 8

What will happen with the controllers on touchdown and what will be the result?

Answer 8

The controllers swap over roles ready for the next flight

Question 9

How is protection of the structure from positive pressurisation damage provided?

Answer 9

Positive pressure relief valves which operate at a set pressure above max differential

Question 10

What pressures are likely to activate the pressurisation protection? (3)

Answer 10

• Over pressure
• Negative pressure
• Excessive cabin altitude

Question 11

What would happen to the outflow valve is the cabin altitude reaches 15000ft?

Answer 11

They should close automatically

Question 12

Which protection circuit of what control system would defend against duct overheat?

Answer 12

Overheat circuit in the zone controller

Question 13

Why is the aircraft pre-pressurised before take off?

Answer 13

• Stabilises the aircraft
• Checks for leaks
• Prevent pressure fluctuations during rotation as airflow hits valves

Question 14

What devices are provided in case there is a depressurisation across zones?

Answer 14

• Equalisation valves

- Blowout doors and panels