11.4 - Air Conditioning and Pressurisation

Question 1

How does the ozone converter work

Answer 1

Catalytic reaction

Question 2

How does coalescer-type water separators work

Answer 2

By encouraging the water to form large droplets that can be centrifuged out

Question 3

In which part of the vapour cycle machine is the heat energy discharged to the atmosphere

Answer 3

Condenser

Question 4

Which is true for an aircraft that is on the ground and pressurisation is in the ground mode

Answer 4

Outflow valves commanded to the fully open position

Question 5

How is the pressure in an aircraft cabin regulated

Answer 5

By the outflow valves regulating the amount of air leaving the cabin

Question 6

What happens in the pressurisation system at aircraft touchdown

Answer 6

The cabin pressure controllers swap rolls and the outflow valves are driven to the fully open position

Question 7

What happens in the event of excess cabin positive pressure

Answer 7

Safety valves open to bleed away pressure

Question 8

What happens when cabin is at 15000ft

Answer 8

The outflow valves are completely closed independent of the normal control system

Question 9

Which circuit defends the air on system from the duct overheat in the event of component failure or mis control in manual mode

Answer 9

The protection circuits of the zone temperature control system

Question 10

Which condition of air is ideal for a pneumatic system

Answer 10

Air at constant pressure and temperature

Question 11

In which condition is the air arriving at the air conditioning packs normally

Answer 11

Approximately 200c at 45psi

Question 12

Considering the very low temperature of the air leaving the air cycle machine. How is it possible to prevent water from freezing in the system

Answer 12

A water separator is located upstream of the cooling pack

Question 13

How is the quantity of air entering the cabin regulated

Answer 13

By the pack valve

Question 14

Which climb mode of pressurisation is usually more comfortable for passengers

Answer 14

External mode

Question 15

Which devices are installed to prevent damage to the structure in the event of sudden depressurisation of the aircraft

Answer 15

Equalisation valves allow pressure in various zones to equalise

Question 16

How is ozone in the air supplied in the air conditioning system treated

Answer 16

Ozone converter incorporates a catalyst that converts ozone to harmless oxygen

Question 17

What is the purpose of the bleed valve

Answer 17

To regulate engine bleed air supply

Question 18

Which statement is true regarding cabin pressure controllers

Answer 18

There are 2 controllers, 1 active and 1 standby

Question 19

From what do the cabin pressurisation systems safety devices protect the fuselage structure

Answer 19

From high positive and negative delta p

Question 20

What cabin pressure is the cabin raised too during cabin pressure leak checks

Answer 20

Approximately 4psi

Question 21

How many different air sources can be used to supply the air conditioning system in flight

Answer 21

2

Question 22

What is the alternative source of the air conditioning system should engine bleed air become available during flight

Answer 22

APU

Question 23

Why is there a requirement for the ventilation of the temperature sensors in the cabin zone

Answer 23

The ventilation delivers the cabin air to the sensor

Question 24

What components does an air cycle machine comprise

Answer 24

A compressor, a turbine and a heat exchanger

Question 25

Why would an OUTFLOW valve have 2 AC motor and 1 DC motor

Answer 25

Each pressure controller can control its own AC motor and if AC is not available the DC motor can control the valve

Question 26

During a cabin pressure leakage test, why must all instructions be adhered to

Answer 26

Injury to personnel inside the cabin could occur as well as damage to pressure sensitive components

Question 27

What circuit controls air conditioning ducts from potential overheat conditions

Answer 27

The protection circuit

Question 28

What will occur if the cabin depressurises

Answer 28

The flight crew are warned to put on their oxygen masks

Question 29

How does an air cycle machine cool the pneumatic flow

Answer 29

The air is cooled by one or more heat exchangers and the turbine which are operated by ram air

Question 30

What is the purpose of a turbine bypass valve in the pack

Answer 30

It controls the mass of air flowing to the pack

Question 31

What is the cabin altitude

Answer 31

The pressure inside the cabin in relation to sea level pressure

Question 32

What is the purpose of the emergency Ram Air Inlet

Answer 32

It supplies fresh ambient air to the mixing unit when all packs fail in flight

Question 33

If ice has built up in the condenser or the exit of the turbine, how is it cleared

Answer 33

Some air is bypassed around the heat exchangers and the air cycle machine though a temperature control valve and melts the ice

Question 34

What type of valve is the pack valve

Answer 34

Venturi type

Question 35

How is the pack valve operated

Answer 35

Electronically opened, spring loaded to close

Question 36

How is the pack vale shut off function controlled

Answer 36

Fire handle, during engine start and from the pack switch

Question 37

What is the minimum volumetric flow allowed per person by the ICAO regulations into the cabin

Answer 37

0.283m3/min

Question 38

What are the two types of Air Cycle Machine

Answer 38

Oil lubricated and air lubricated

Question 39

What operation does the Trim Air Valve perform

Answer 39

They control the bleed air directly fed into the mixing chamber

Question 40

Wheat happens to the ram air doors during flight

Answer 40

They modulate to reduce both the ram air flow and drag

Question 41

What are the components of a Vapour Cycle Machine

Answer 41

The refrigerant, the compressor, the condenser, the expansion valve and the Evaporator

Question 42

What refrigerant has replaced R12

Answer 42

Tetrafluoroethane (R134a) which is classed as safer for the environment

Question 43

Can R12 and R134a be mixed

Answer 43

No, nor can one be used in a system designed for the other

Question 44

Where is the condenser in the system

Answer 44

Located downstream of the condenser and upstream of the expansion valve

Question 45

What is inside the receiver dryer

Answer 45

Filters and desiccant material

Question 46

How does air get into the evaporator

Answer 46

The evaporator is situated in such a way that cabin air is pulled into it by a fan

Question 47

What drives the compressor

Answer 47

Modern compressors are either engine driven or driven by an electric motor

Question 48

What are cabin temperature pick up units and duct temperature sensors

Answer 48

Thermistors

Question 49

What is the temperature selector

Answer 49

A rheostat

Question 50

In the venturi system, where does the humidifier get its water supply

Answer 50

Potable water supply

Question 51

How much air normally filtered and recirculated

Answer 51

Up to 50%

Question 52

Where is the cabin air normally exhausted from

Answer 52

Most aircraft this exhaust is extracted from the lower compartments after of the wings by outflow valves and fwd of the wings by the recirculation fans

Question 53

Cabin pressurisation systems are designed to produce conditions of how many ft?

Answer 53

Approximately 8000ft or less

Question 54

At what cabin altitude must people use oxygen

Answer 54

Flight crew 10,000ft Passengers 15,000ft

Question 55

Why do the regulations limit the maximum cabin altitude during flight to 8000ft

Answer 55

A compromise between acceptable environmental conditions and the structural stress applied to the fuselage

Question 56

What is atmosphere pressure at sea level

Answer 56

1 atm 14.7 psi 29.92 Hg 1013.2 hPa 1013.2 mb 760 mm Hg

Question 57

What is the rate of change in temperature with altitude in the troposphere

Answer 57

-2’C for every 1000 ft

Question 58

What are the different modes of operation for cabin pressurisation

Answer 58

Isobaric mode - maintains altitude as set by aircrew Differential - maintains cabin pressure to a constant pressure difference with ambient Manual - used for trouble shooting

Question 59

When in isobaric mode, what happens if the aircraft climbs beyond a certain altitude and maintains the cabin altitude selected my result in a differential pressure above what the fuselage was designed

Answer 59

Switches from isobaric to differential mode

Question 60

What is the normal cabin pressure rate of change

Answer 60

Normal climb - 500 fpm Normal descending - 300 fpm

Question 61

When do cabin safety valves open

Answer 61

When pressure differential is between 8 and 10 psi approximately

Question 62

When do negative differential pressure valves open

Answer 62

When the outside pressure exceeds the inside by 0.5 - 1.0 psi

Question 63

Can you release refrigerant into the atmosphere

Answer 63

R12 is illegal to release R134a is illegal in some countries

Question 64

What are the health implications of inhalation of R134a

Answer 64

Inhalation of high quantities of R134a vapour may cause cardiac irregularities, unconsciousness and death

Question 65

What gauges are on the manifold

Answer 65

Low pressure 0 -150 psi with blue hose High pressure 0 - 500 psi with red hose

Question 66

How much pressure is required for a leak check

Answer 66

About 50psi

Question 67

What are the normal pressures in the system

Answer 67

Low pressure 10 - 50 psi High pressure 125 - 250 psi

Question 68

How is bleed air leak monitored

Answer 68

Flight deck gauges Overheat detection located near the ducts Bleed are monitoring system detect loss of pressure

Question 69

What would cause the pack overheat warning to be displayed

Answer 69

Outlet temp of more than 260c or outlet temp of more than 230c four times in one flight