11.4 Air Conditioning And Pressurisation Flashcards
What do pneumatic systems deal with on aircraft
They deal with compressed or pressurised gas as a source of power.
Typically the gas used is air
On aircraft what would pneumatic power or energy be used for
Engine starting, cabin pressurisation, air conditioning, wing de-icing, water reservoirs and hydraulic reservoir pressurisation
What two variables need to be as constant as possible in a pneumatic system to support the different consumers effectively
Pressure and temperature
What is the main air source on jet aircraft
The engine compressor provides enough air for combustion purposes and also the pneumatic system
What is compressed air which has come from the engines called?
Bleed air
When on the ground the aircraft can be supplied by external air.
How would it be delivered
Via high pressure ground connectors
As the engines thrust varies what is needed to keep a constant pressure for the pneumatic consumers
A pressure regulator
What is the engine pressure regulator also known as
The bleed valve
What is used to protect the HP compressor from back flow when it bleeds air
A check valve
What type of valves are used for APU bleed air supply
No pressure regulator valve is needed but a shut off valve called the APU bleed valve is used to provide or shut off bleed air from the APU.
A check valve is also used to prevent back pressure
What is used to cool bleed air from the engines
A pre cooler
Where does the air for the pre cooler come from?
A duct directly from the fan air
What is used to allow more or restrict the amount of fan air to pass the pre cooler
A fan air valve
What is used to connect all engines bleed air and APU bleed air
Cross Bleed manifold
What is used to isolate left to right wing ducts on the manifold
A cross bleed valve
How do the pneumatic ducts detect leaking
They are monitored by a leak detection system
How would you control the pneumatic system or users
Manually via pneumatic control panel in the cockpit or automatically via the pneumatic controller
What is a pneumatic controller
To monitor pressure and temperature, detect leaks and monitor the operation of pneumatic components
There is one per engine
What condition would you be effected from if you climbed to high altitude in an aircraft which is unpressurisedk
You would be affected by Hypoxia
In passenger aircraft what is the purpose of cabin pressurisation
Keeping passengers comfortable
What does pressure differential mean
The difference in pressure between cabin/cockpit and outside of the aircraft
What provides pressurisation to the cabin, flight deck, cargo and avionics compartments
The air conditioning system
What main areas are not pressurised
Landing gear bays, the radomes and tail cone
Can different aircraft zones be heated individually heated
Yes
What 5 things must the air con system ensure that air is ?
- Fresh
- Clean
- At a comfortable temperature
- At the correct humidity
- At the correct pressure
What are the regulation relating to freshness on board
Regulations say on average ad acceptable amount of fresh air supplied should be 0.283 cubic meters per person per minute
According to regulations how often should air be exchanged
3-5 mins
What are used to keep air clean and safe
Air filters and ozone converters
What is the comfortable temperature range for air temp
18-30 degrees Celsius
What temperature air holds more water warm or cold
Warm
What two things is pressurisation a compromise between
Passenger comfort and structural strength
What are cabins usually pressurised to
8000ft
What is the cabin pressure regulated by
Outflow valves
The temperature of air delivered to the zones is regulated in two steps, what are they
Pack controllers control the temperature the air leaves the pack and zone controllers regulate the amount of trim air is mixed with the cold air
Where are the pack and zone controllers located
The avionics compartment
What are the 3 types of cooling device on an aircraft
- Heat exchanger
- Vapour cycle machine
- Air cycle machine
What process is heat exchanged in a heat exchanger
Conduction
When are vapour cycle machines used
When bleed air is not available
What type of aircraft would you find a vapour cycle machine
Small propeller aircraft, aircraft with out APU or older aircraft
What is a pack valve and what is it also known as
A flow control valve. It is spring operated and determines how much air goes into the cabin
It is also known as pack flow control valve or FCV
What must ALWAYS be done before you put on the pack switch
Follow a checklist
What is the density of air at 8000ft
0.96 kg/m3
What is the most efficient ways air con systems save energy
By adjusting the airflow to the number of consumers
When the pack selector is selected to normal what % of airflow is the cabin receiving
100%
When the pack selector is in the high position what % of air is being delivered to the cabin
More than 100%
When the pack selector is in the LO position what % of air is the cabin receiving
80%
What is the main advantage of the two heat exchangers being mounted together
Only one cooling duct is necessary
What are the 3 main components of the air cycle machine
- Compressor
- Turbine
- Fan
How is the air cycle machine lubricated
There is no need for lubrication as it uses air bearings
What are air cycle machines also known as
Boot strap air cycle machines
How can you adjust the temperature in the pack
By using the turbine bypass valve built in
What is a turbine bypass valve also called
Temperature control valve
How is the turbine bypass valve operated
Always electrically
What type of valve is the turbine bypass valve
A butterfly type with a manual override which also operates as a position indicator
What is ram air used for
It is used as cooling air
What are the ram air inlets and outlets called
RAI (ram air inlet) and ram air exit
What type of inlet is the ram air inlet
NACA type
Why would a fan be needed in the ram air system
The fan is located on the common shaft of the turbine and the compressor
The fan is used on the ground as there is no ram air effect
As it is on the common shaft, if the packs are on the fan is turning
Why must water be removed from the air con system
As temperatures can fall as low as -50 could cause freezing and damage
Where does water separating occur
The water separator in the cooling pack
What are the two ways water can be separated
High pressure loop or low pressure loop
Depending on manufacturer
What is the purpose of the jet pump
It sprays the condensed water into the ram air inlet duct. This condensed water increases the cooling efficiency of the heat exchanger
What causes the droplets to collect in the drain sump of the water separator
Centrifugal force
In a high pressure loop what is used to detect icing of the condenser
Differential pressure and anti ice valve
How many pack controllers does an air con pack have
1 main and 1 redundancy
What are the 3 minimum required sensors in a pack
- Compressor discharge temperature sensor
- Pack discharge temperature sensor
- Compressor overheat switch
What does the pack controller monitor
The pack flow control valve position and sends it to the EICAS or ECAM indication
How is the ram air inlet door measured
With limit switches and a position potentiometer
How is optimum pack outlet temperature achieved
It is achieved by the pack controller modulating the bypass valve, the ram inlet door and the ram outlet door
In flight, for maximum cooling, what is the position of the ram inlet doors and the bypass valve
Ram air doors are open and the bypass valve is fully closed
What are the 3 examples of failures that occur in a pack
- Controller failure
- Compressor overheat
- Bypass valve failure
If the compressor overheat sensor detects a temperature which is close to overheat what would be done to increase cooling
The ram air doors would be opened further
Would type of message would indicate in the cockpit as a result of an overheat
A FAULT on the pack switch, they pilot would have to turn off the pack and use the backup pack
Where does the treated cold air go after the packs have done their job
A mixing unit which distributes it to the aircrafts different zones
What is another term for a mixing unit
Plenum chamber
What is mixed in the mixer unit
Fresh air from the packs and discharged cabin air
What is the passengers individual air supply system called
The gasper system
What is the system called that is carried out by the mixer unit. (Mixing fresh pack air with discharged cabin air)
The recirculation system
What is the purpose of the recirculation fans
The fans suck discharged cabin air from under the floor area, clean it with filters and feed it into the mixing unit
How would you get conditioned air on the ground if the packs are not used
You can supply conditioned air directly to the mixing unit via a ground connector port
If all packs fail in flight what would be done to ensure that the passengers would still have air to breathe
Open the emergency ram air inlet.
It has an electrical actuator that extends the inlet flap into the ambient airflow
What parameters can affect cabin temperature
- The ambient temperature
- Radiation from the sun
- Cabin insulation
- Heat from equipment
- Heat from passengers
- Temperature and rate that air is supplied to the cabin
To allow for individual control of all zone temperatures what is required
A trim air system
What is the purpose of pack valves
They are flow control and shut off valves
With regards to automatic temperature control, what’s is the name of the computer that controls the temperature for that zone
The zone controller
What is the ‘Anticipator’
a special temperature rate sensor found in some circuits
What protects the system from duct overheat in the event of manual mode or component malfunctions
The protection circuits
What type of sensors are used in the temperature zone system
Thermistor type
What must be done for the sensors to read the temperature accurately
They must be ventilated, usually done by an electrical fan
What are the typical indications on an air conditioning page in the flight deck
- Actual cabin temperature
- Actual duct temperature
- Actual trim air valve position
On the control panel what button is used to reset the trim air system
HOT air
What are the main ventilation systems on aircraft
- For galleys and lavatories (remove humid and stale air)
- Cargo compartments (used especially when carrying live cargo)
There is also a separate system for equipment cooling
What 4 subcategories does cargo ventilation fall in to
- Non ventilated cargo
- Ventilated and heated cargo
- Ventilated and unseated cargo
- Air conditioned cargo
What happens to the air in a ventilated cargo compartment
It travels through exit grills and through the cargo hold. The air is then extracted by fans and dumped overboard by outflow valves
In a ventilated cargo compartment what must be done in the case of a fire
Two motor operated isolation valves must close to prevent airflow and starve the fire
What are the two methods of heating a heated and ventilated cargo bay
- Bleed air
- Electric heater
What are the two temperature selections that can be made for a heated cargo bay
7 degrees or 21 degrees
What would happen if an overheat in a cargo compartment occurs
An overheat circuit is activated and the light on the heat cargo aft button will illuminate arming the extinguishers
Where does the air come from for the air conditioned cargo bay
Most comes from the cabin through an inlet isolation valve
What removes air from the galleys and lavatories
Extraction fans
For equipment cooling valves are used to carry air flow what would happen in the case of smoke
Extra valves are opened and an override valve
When pressurising the cabin what rate or pressurisation and depressurisation should the aircraft not exceed
Positive cabin rate should not exceed 500ft/min
Negative cabin rate should not exceed 300ft/min
Protection functions must become active when when there is an excess in cabin altitude or excessive differential pressure.
What 3 things must happen at different altitudes
> At 10,000ft - Flight crew gets a warning to put on oxygen masks
> At 14,000ft - Oxygen masks automatically deploy in the cabin
> At 15,000ft - The outflow valves must close automatically
What are the positive pressure relief valves for
To prevent structural stress on the aircraft. The re must be 2 safety valves and they are usually located on the aft pressure bulkhead
What is used to prevent pressure differences in cargo bay areas
Spring loaded flapper valves will open at a predetermined value
What are the 3 modes that the pressurisation of the aircraft works on
- Automatic
- Semi automatic
- Manual
What is the main input that is required when in semi automatic mode (Pressurisation)
The landing field elevation must be entered manually
When would you have to select manual pressurisation mode
When both pressure controllers fail in flight.
Manual mode will require manually controlling outflow valves with a toggle switch
What is the ditching button used for
To isolate the cabin from water entering during an emergency landing on sea (outflow valves close)
What position are the outflow valves when the aircraft is on the ground
Fully open to avoid accidental cabin pressurisation
The equipment cooling valves are also open
What controls cabin pressurisation in automatic mode
The cabin pressure controller
When the aircraft leaves the ground what activates ground mode
Air ground logic
In inertial climb mode the cabin controller calculates the cabin rate in proportion with aircraft altitude ( so they go up linear together I.e when at 40,000ft the max cabin altitude is reached on 8,000ft). What is this mode also called
Proportional mode
What mode of pressurisation is more comfortable for passengers
The external climb mode
The external climb mode controller calculates a smooth and constant cabin rate
After touchdown, which is detected by the ground air logic the controller switches back to ground mode, what should also happen
Outflow valves should go to fully open
In aircraft with 2 cabin pressure controllers what should happen to them after every flight
They swap roles. The primary becomes the standby and vice versa
How many forms of power do the outflow valves have
2 AC and 1 DC
When pressure controller one is primary it will use AC1
When pressure controller 2 is primary it will use AC2
When selected to manual DC is used to ensure power is available in emergency
Before carrying out a cabin pressure leakage test what must be done
To prevent damage pressure sensitive equipment must be removed I.e computers with pressure ports, oxygen regulators and masks, sensitive pressure switches, fluid tanks like water tanks and auxiliary fuel tanks
When doing a cabin pressurisation leak test what ATA chapter in the AMM must be read
Chapter 5
