11.4 - Air Conditioning and Pressurisation Flashcards
How does the ozone converter work
Catalytic reaction
How does coalescer-type water separators work
By encouraging the water to form large droplets that can be centrifuged out
In which part of the vapour cycle machine is the heat energy discharged to the atmosphere
Condenser
Which is true for an aircraft that is on the ground and pressurisation is in the ground mode
Outflow valves commanded to the fully open position
How is the pressure in an aircraft cabin regulated
By the outflow valves regulating the amount of air leaving the cabin
What happens in the pressurisation system at aircraft touchdown
The cabin pressure controllers swap rolls and the outflow valves are driven to the fully open position
What happens in the event of excess cabin positive pressure
Safety valves open to bleed away pressure
What happens when cabin is at 15000ft
The outflow valves are completely closed independent of the normal control system
Which circuit defends the air on system from the duct overheat in the event of component failure or mis control in manual mode
The protection circuits of the zone temperature control system
Which condition of air is ideal for a pneumatic system
Air at constant pressure and temperature
In which condition is the air arriving at the air conditioning packs normally
Approximately 200c at 45psi
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
A water separator is located upstream of the cooling pack
How is the quantity of air entering the cabin regulated
By the pack valve
Which climb mode of pressurisation is usually more comfortable for passengers
External mode
Which devices are installed to prevent damage to the structure in the event of sudden depressurisation of the aircraft
Equalisation valves allow pressure in various zones to equalise
How is ozone in the air supplied in the air conditioning system treated
Ozone converter incorporates a catalyst that converts ozone to harmless oxygen
What is the purpose of the bleed valve
To regulate engine bleed air supply
Which statement is true regarding cabin pressure controllers
There are 2 controllers, 1 active and 1 standby
From what do the cabin pressurisation systems safety devices protect the fuselage structure
From high positive and negative delta p
What cabin pressure is the cabin raised too during cabin pressure leak checks
Approximately 4psi
How many different air sources can be used to supply the air conditioning system in flight
2
What is the alternative source of the air conditioning system should engine bleed air become available during flight
APU
Why is there a requirement for the ventilation of the temperature sensors in the cabin zone
The ventilation delivers the cabin air to the sensor
What components does an air cycle machine comprise
A compressor, a turbine and a heat exchanger
Why would an OUTFLOW valve have 2 AC motor and 1 DC motor
Each pressure controller can control its own AC motor and if AC is not available the DC motor can control the valve
During a cabin pressure leakage test, why must all instructions be adhered to
Injury to personnel inside the cabin could occur as well as damage to pressure sensitive components
What circuit controls air conditioning ducts from potential overheat conditions
The protection circuit
What will occur if the cabin depressurises
The flight crew are warned to put on their oxygen masks
How does an air cycle machine cool the pneumatic flow
The air is cooled by one or more heat exchangers and the turbine which are operated by ram air
What is the purpose of a turbine bypass valve in the pack
It controls the mass of air flowing to the pack
What is the cabin altitude
The pressure inside the cabin in relation to sea level pressure
What is the purpose of the emergency Ram Air Inlet
It supplies fresh ambient air to the mixing unit when all packs fail in flight
If ice has built up in the condenser or the exit of the turbine, how is it cleared
Some air is bypassed around the heat exchangers and the air cycle machine though a temperature control valve and melts the ice
What type of valve is the pack valve
Venturi type
How is the pack valve operated
Electronically opened, spring loaded to close
How is the pack vale shut off function controlled
Fire handle, during engine start and from the pack switch
What is the minimum volumetric flow allowed per person by the ICAO regulations into the cabin
0.283m3/min
What are the two types of Air Cycle Machine
Oil lubricated and air lubricated
What operation does the Trim Air Valve perform
They control the bleed air directly fed into the mixing chamber
Wheat happens to the ram air doors during flight
They modulate to reduce both the ram air flow and drag
What are the components of a Vapour Cycle Machine
The refrigerant, the compressor, the condenser, the expansion valve and the Evaporator
What refrigerant has replaced R12
Tetrafluoroethane (R134a) which is classed as safer for the environment
Can R12 and R134a be mixed
No, nor can one be used in a system designed for the other
Where is the condenser in the system
Located downstream of the condenser and upstream of the expansion valve
What is inside the receiver dryer
Filters and desiccant material
How does air get into the evaporator
The evaporator is situated in such a way that cabin air is pulled into it by a fan
What drives the compressor
Modern compressors are either engine driven or driven by an electric motor
What are cabin temperature pick up units and duct temperature sensors
Thermistors
What is the temperature selector
A rheostat
In the venturi system, where does the humidifier get its water supply
Potable water supply
How much air normally filtered and recirculated
Up to 50%
Where is the cabin air normally exhausted from
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
Cabin pressurisation systems are designed to produce conditions of how many ft?
Approximately 8000ft or less
At what cabin altitude must people use oxygen
Flight crew 10,000ft
Passengers 15,000ft
Why do the regulations limit the maximum cabin altitude during flight to 8000ft
A compromise between acceptable environmental conditions and the structural stress applied to the fuselage
What is atmosphere pressure at sea level
1 atm
14.7 psi
29.92 Hg
1013.2 hPa
1013.2 mb
760 mm Hg
What is the rate of change in temperature with altitude in the troposphere
-2’C for every 1000 ft
What are the different modes of operation for cabin pressurisation
Isobaric mode - maintains altitude as set by aircrew
Differential - maintains cabin pressure to a constant pressure difference with ambient
Manual - used for trouble shooting
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
Switches from isobaric to differential mode
What is the normal cabin pressure rate of change
Normal climb - 500 fpm
Normal descending - 300 fpm
When do cabin safety valves open
When pressure differential is between 8 and 10 psi approximately
When do negative differential pressure valves open
When the outside pressure exceeds the inside by 0.5 - 1.0 psi
Can you release refrigerant into the atmosphere
R12 is illegal to release
R134a is illegal in some countries
What are the health implications of inhalation of R134a
Inhalation of high quantities of R134a vapour may cause cardiac irregularities, unconsciousness and death
What gauges are on the manifold
Low pressure 0 -150 psi with blue hose
High pressure 0 - 500 psi with red hose
How much pressure is required for a leak check
About 50psi
What are the normal pressures in the system
Low pressure 10 - 50 psi
High pressure 125 - 250 psi
How is bleed air leak monitored
Flight deck gauges
Overheat detection located near the ducts
Bleed are monitoring system detect loss of pressure
What would cause the pack overheat warning to be displayed
Outlet temp of more than 260c or outlet temp of more than 230c four times in one flight
