11.4 - Air Conditioning Flashcards
1
Q
What resources of air are there on an aircraft? (2 in flight and on ground, 1 on ground only)
A
- Engine bleed air
- Auxiliary power unit
- High pressure ground connectors
2
Q
What 3 types of air can be taken from the engine?
A
- Fan air
- Intermediate Pressure
- High pressure
3
Q
What does the check valve on the intermediate pressure stage protect against, and when is it used?
A
Protects the compressor from back flow (compressor stalls), when air is being taken from the high pressure stage
4
Q
What does the fan air valve do?
A
Allows more or less fan air to pass the precooler
5
Q
Through what 2 methods (one manual, one automatic), is control of the pneumatic system achieved?
A
- Pneumatic control panel in flight deck
- Pneumatic controller
6
Q
How many pneumatic controllers is there on each engine bleed air system?
A
One on each engine
7
Q
What areas of the aircraft does the air conditioning pressurise? [4]
A
- Passenger compartment
- All cargo compartments
- Flight deck
- Avionic compartments
8
Q
How often must cabin air be exchanged to ensure freshness?
A
Every 3 - 5 minutes
9
Q
What 2 devices are fitted to keep air clean?
A
- Air filters
- Ozone converters (at high altitudes)
10
Q
What is the permitted temperature range to ensure passenger comfort?
A
18-30 degrees C
11
Q
Why is water separated from the air? (2 reasons)
A
- Prevents parts and valves freezing
- Stops fog and water droplets forming in the cabin
12
Q
What is considered the ideal cabin altitude?
A
8000 feet
13
Q
What valve regulates the flow of bleed air from the pneumatic system into the air conditioning system?
A
Pack valves
14
Q
What do air conditioning packs do to pneumatic bleed air?
A
Cool it to a basic temperature
15
Q
What does the mixing unit, mix?
A
Cool air from the packs with recirculated cabin air
16
Q
What is trim air?
A
A certain amount of hot air that comes from up stream of the packs that makes the final adjustment to the temperature of the air leaving the mixing unit
17
Q
What do pack controllers regulate?
A
The temperature of cold air leaving the pack
18
Q
What 3 functions do zone controllers have?
A
- Regulate the amount of trim air mixed with cold air from the packs
- Regulate temperature by comparing actual cabin temperature with selected zone temperature set by flight crew
- Define the temperature of the cooler air and send this info to the pack controller
19
Q
Where are there air conditioning packs, valves and mixing units located on the aircraft?
A
In the centre wing box area
20
Q
What are the 3 types of cooling device found on the aircraft?
A
- Heat exchanger
- Air cycle machine
- Vapour cycle machine
21
Q
What is the disadvantage of heat exchangers?
A
They do not have sufficient power to cool all of the cabin air, especially on the ground
22
Q
When are Vapour cycle machines used?
A
When engine bleed air is not available
23
Q
What does a pack check valve do?
A
Prevents backflow into the pack when the pack is shutdown
24
Q
What type of valve is a pack valve and how is it controlled? [2]
A
- Venturi-type butterfly valve
- Controlled by a Solenoid
25
How is a pack valve operated and how is it held closed? [2]
- Pneumatically operated
| - Spring loaded to closed position
26
In what 3 situations is the Pack Valve controlled to close? (Shut-off function)
- When the fire handle is pulled
- During engine start
- When the pack switch is operated
27
What indicates if a Pack valve is fully open or closed?
An in built micro-switch
28
What does the Pack Valve manual override allow?
The pack valve to be locked in the closed position
29
What happens to the Pack Valve when the electrical power supply is lost?
It opens automatically (fail-safe philosophy)
30
If an aircraft is fully loaded with passengers, what setting is selected on the Push button on the flight deck air conditioning panel?
Hi flow (Pack Valve opens further)
31
If an aircraft is not fully loaded with passengers, what setting is selected on the Push button on the flight deck air conditioning panel?
Low Flow (Pack Valve closes partially)
32
On aircraft capable of selecting High, Medium and LO airflow, what is the percentage of airflow supplied to the cabin for each?
- High=Over 100%
- Medium=100%
- LO=80%
33
How many heat exchangers do modern Packs have?
2
34
What is the advantage of mounting heat exchangers close together?
Only one cooling duct is necessary
35
What are the 3 primary components of an air cycle machine?
- Compressor
- Turbine
- Fan
36
Why is lubrication of air cycle machines limited?
They use air bearings
37
What does the Bypass valve in the pack do?
Adjusts temperature in the pack by determining the air mass to the turbine
38
What type of valve is the bypass valve in the pack?
Butterfly type (with a manual override)
39
How is the bypass valve in the pack always operated?
Electrically by the Pack controller
40
What happens to the bypass valve in the pack if turbine outlet temperature is too high?
It closes more
41
What happens to the bypass valve in the pack if turbine outlet temperature is too low?
It opens more
42
What does the position of the ram air door effect?
The cooling effect of the heat exchangers
43
What 3 positions can the ram air door be in?
- Open
- Modulating
- Closed
44
What type of intake is the ram air inlet?
NACA type air intake
45
What is used to open and close ram air inlet and exit doors?
Electrically driven actuators
46
Why is a fan required as part of the ram air system?
For ground use as there is no ram effect
47
Which two systems can be used to separate water?
- High Pressure loop
| - Low Pressure loop
48
Where is separated water sent?
To the ram air inlet duct to increase heat exchanger cooling efficiency
49
What is the first step of low pressure water separation?
Air passes through a coalescer which combines the water particles into droplets. The air is circulated by swirl vanes and the droplets are forced centrifugally into the collector to be drained away.
50
What is built in to the coalescer in case it becomes clogged with dirt or ice?
A pressure relief valve that allows air to bypass the coalescer
51
How is ice formation on the coalescer prevented?
By controlling air temperature to the water separator
52
What is a water aspirator and what does it do?
A type of jet pump mounted at the heat exchanger cooling air inlet that sprays separated water into the airflow
53
Where are the Pack controllers normally located?
In the electric and electronic compartment
54
What are the 3 sensors that must be built into a pack as a minimum?
- Compressor discharge temperature sensor
- Pack discharge temperature sensor
- Compressor overheat switch
55
How does the pack controller influence the bypass valve?
Sends signals for it to open or close more depending on the temperature required
56
How is ram air inlet door position measured?
By limit switches and a position potentiometer
57
What 4 things does the pack controller receive signals from?
- Pack flow control valve
- Bypass Valve
- Ram air inlet door
- Ram air exit door
58
What does the zone controller do during normal operation?
Receives information from sensors in the cabin and then sends the required pack temperature demand to the pack controller
59
What are 3 example failure conditions that can occur in the pack?
- Compressor failure
- Compressor overheat
- Bypass Valve failure
60
What happens if a pack controller fails?
The backup pack controller takes over
61
What happens if the Compressor overheat sensor detects a temperature exceeding prescribed values?
Ram air doors open further, if this fails to reduce temperature, the pack controller reduces airflow through the pack by controlling the flow control valve towards the closed position, reducing airflow and temperature as a result
62
What does the Mixing unit do?
Let’s Pack Air mix with recirculated cabin air and directs mixed air through the primary supply ducts to the different aircraft zones
63
How is Air from the mixer unit distributed around the aircraft?
Flows along primary supply ducts located horizontally along the fuselage then through riser ducts located vertically along the fuselage then through outlets in the cabin into each zone
64
What are the two methods of supplying air to the flight deck?
- Take air direct from the pack before the mixer unit
| - Take Air from the mixer unit via a separate supply duct so it only supplies fresh conditioned air
65
What is an individual passenger air supply system known as?
A Gasper system
66
What do recirculating fans do?
Suck discharged cabin air from the underfloor area, clean it with filters and feed it back to the mixing unit
67
Where are electric heaters located in the flight deck and in the cabin? [2]
- On some air outlets in the flight deck
| - In passenger cabin to heat fuselage
68
What does the emergency ram air inlet do and when is it used? [2]
- Extends via electrical actuator to guide fresh ambient air into the mixing unit
- Used only if all packs fail
69
What is the trim air valve?
An electrically operated valve that controls the amount of hot trim air that is mixed with the cold supply air
70
What is installed in a trim air system to minimise the effect of pressure changes from the trim air valves?
A pressure regulating valve
71
What happens when the trim air pressure regulating valve closes?
All trim air valves also close
72
Where are zone temperature sensors installed?
In the cabin ceiling area
73
What are the 3 indications in a typical air conditioning systems page?
- Actual cabin temp measured by temp sensors in the cabin
- Actual duct temp measured by duct temp sensors
- Actual trim air valve position measured by potentiometers in the valve
74
What is the ‘HOT AIR’ push button on the control panel used for?
To switch on or reset the trim air system
75
What are the 4 different ventilation types of cargo compartment?
- Non-Ventilated Cargo compartment
- Ventilated and heated Cargo compartment
- Ventilated and Unheated Cargo compartment
- Air conditioned Cargo compartment
76
How are the lavatory and galley ventilated? [3]
- Cabin air enters through a grill in the door
- Air is extracted through a ceiling duct
- Small amount of fresh conditioned air comes from a separate duct in the cabin distribution system
77
What is a skin heat exchanger?
A duct or duct system directly under the aircraft skin. Warm air flows through and is cooled by the cold skin at high altitudes
78
When the equipment cooling system works automatically, what are it’s two normal modes?
- Inboard: Exhaust Air goes to underfloor area or forward Cargo compartment
- Outboard: Exhaust Air goes out of the aircraft (normally used on the ground)
79
How is electrical equipment cooled in outboard mode?
By ambient air from outside the aircraft which enters through skin air inlet valve and exits via the extractor valve. Or by cabin air if ambient air is cold enough to damage the equipment
80
When does an equipment cooling override operation occur and what must the crew do?
- When the equipment cooling system has a component failure or smoke is detected
- The crew must manually operate the cooling system
81
What does the low flow detector in the equipment cooling system do?
Detects a low flow situation caused by a damaged fan for example and sends this information to the equipment cooling system computer which displays a caution message on the ECAM or EICAS display
82
How is pressure on an aircraft regulated?
By one or more outflow valves that limit the air leaving the aircraft
83
What happens before cabin altitude reaches 10,000ft?
Flight crew receives a warning to put on oxygen masks
84
What happens when cabin altitude reaches 14,000ft?
Oxygen masks are automatically released from the passenger cabin ceiling
85
What happens when cabin altitude reaches 15,000ft?
Outflow valves close automatically, independent of the normal control signal to try and maintain pressure
86
What safety measure is in place to protect the aircraft from structural damaged caused by increased differential pressure?
At least 2 safety valves (aka positive pressure relief valves) that open on a spring when differential pressure exceeds an allowable value (around 8.5psi) and closes once diff pressure is back in limits
87
What is negative differential pressure and why is it so dangerous? [2]
- When ambient pressure is higher than cabin pressure
| - Dangerous because the fuselage is only constructed to withstand positive differential pressure
88
How is negative differential pressure prevented?
By a negative pressure relief valve that opens as soon as ambient pressure exceeds cabin pressure
89
What function do equalisation valves serve?
Preventing differential pressure building up between sealed cargo compartments and the cabin and damaging the walls
90
What safety measure activates in the event of a rapid pressure change between compartments that exceeds the limits of the equalisation valve?
Blow out panels that blow out of their frames to equalise pressure quickly
91
What 3 modes does the cabin pressurisation system operate in?
- Automatic
- Semi-automatic
- Manual
92
What controls cabin pressurisation in automatic and semi-automatic mode?
One of the two redundant Cabin Pressure Controllers (CPCs)
93
What happens if both cabin pressure controllers fail?
The crew gets a failure message and must select the manual mode
94
How do the crew control pressurisation in manual mode?
Using a toggle switch that is spring loaded to neutral to directly control the outflow valves
95
What happens when the crew press the ditching push button?
All valves below the flotation line of the aircraft and all pack valves close to prevent water from entering
96
How does the cabin pressure controller calculate altitude?
- Receives Pressure from the air data system or static port
| - Converts Pressure into altitude
97
What is a barometric correction?
An adjustment made to the altitude calculated by the cabin pressure controller based off pressure influencing weather conditions
98
How is a barometric correction signal selected? [2]
- Automatically by the flight management or air data system
| - Manually selected on the pressurisation panel
99
When does the pressurisation system start the ‘pre-pressurisation mode’?
When take off is initiated or, on certain aircraft, when the aircraft accelerates to a certain speed
100
What happens during pre-pressurisation?
The cabin pressure is increased, taking the cabin altitude to below the actual altitude to stabilise the fuselage and test for leaks
101
How does pressurisation occur in internal climb mode?
Cabin altitude is Raised proportionally to the actual altitude so maximum cabin altitude (8000ft) will be reached when the aircraft reaches its maximum flight altitude (40,000ft for example)
102
How does pressurisation occur in external climb mode?
The controller calculates a smooth and consistent cabin rate which is more comfortable for the passengers based on information from the flight management system
103
What 2 abnormal conditions can stop external climb mode?
- No flight management data available (switches to internal mode)
- The pilot interrupts the climb and descends (activates abort mode)
104
What occurs during abort mode?
Cabin altitude is automatically decreased to the value for landing at the target airport, decreasing pilot workload during unplanned flight abortion
105
When does the pressure controller switch to cruise mode?
When the aircraft reaches the top of climb or when the pilot stops the climb earlier (due to advice from ATC etc.)
106
What happens during cruise mode?
Cabin altitude is regulated to a determined level, usually the cabin altitude with the maximum differential pressure to enhance passenger comfort
107
What does the safety margin in cruise mode allow?
Cabin altitude to remain constant even when the aircraft makes small altitude changes
108
What additional data from the flight management computer does the controller require when external descent mode is enabled? [2]
- landing field elevation
| - time to arrival at airport
109
What is the final cabin altitude calculated to in descent mode?
100-200ft below field elevation (same reason as pre-pressurisation)
110
When is internal descent mode used and what does it involve? [2]
- When no flight management system data is available
| - Field elevation must be selected manually
111
What happens to the pressurisation mode if touch down is detected by the air ground logic?
It automatically switches to ground mode and the outflow valves fully open, depressurising the aircraft over a defined time period
112
What occurs in aircraft with 2 cabin pressure controllers on touch down?
The controller in command switches, the standby becomes the active and vice versa
113
What are the 2 main components of a safety valve with an over pressure and negative pressure relief function
- Controller assembly
| - Diaphragm assembly (normally pressed by a spring into the valve body)
114
What happens to a safety valve during normal operation?
It is kept closed by a spring force, assisted by cabin pressure, ensuring no cabin air can flow to ambient and vice versa
115
What happens to the safety valve when the positive differential pressure limit is exceeded?
The controller assembly vents the control chamber to ambient, decreasing pressure above the diaphragm. This allows cabin pressure to lift the diaphragm and releases excess cabin pressure to ambient
116
What happens to the safety valve during negative differential pressure?
The higher ambient pressure lifts the diaphragm, allowing ambient air to enter the cabin and equalise the pressure
117
During a cabin leak check how much is the cabin pressurised above the ambient pressure?
4psi
118
What precautions must be taken before and during a cabin leak to avoid damaging pressure sensitive equipment? [3]
- Remove Pressure Sensitive equipment like the oxygen regulator and masks where possible
- Either remove computers with cabin pressure ports or close the ports
- Fill water tanks to protect them from pressure damage
119
What general safety precautions must be taken when doing a pressure leak test? [4]
- Inform other personnel
- Put up safety barriers
- Station someone outside to monitor the aircraft and flight deck personnel
- Switch on the aircraft beacon lights
120
What can indicate that the cabin is pressurised on some aircraft?
A red warning light on the door will illuminate
