Air Con & Pressurisation Flashcards
Where are the air conditioning packs located?
In the main landing gear fairings
Work independently of each other
What pack supplies the flight deck/cabin?
Left pack - flight deck
Right pack - cabin
In the event of a failure one pack can supply both compartments
What is the Air Cycle Machine?
One on each side of the aircraft
Adjusts the air to the proper temperature for the cabin and flight deck
Air then flows to a mixing chamber located under the floor and is mixed with ambient cabin air
How is air distributed to the cabin?
From the mixing chamber through overhead ducts which route the air to eyeball vents
How is air evacuated from the cabin?
Through guides along the floor of the left cabin side
Part of the air is recirculated through the cabin via fans
The remainder is exhausted overboard through outflow valves located on underside of the fuselage
How is the loo ventilated?
Through a vent line
Airflow is generated by cabin differential pressure
How is cabin pressurisation maintained?
By constricting the amount of air that is exhausted overboard
Outflow valves are located on the bottom side of the aft fuselage
What is the normal flow mode?
Constant 22 psi of pressure delivered to the packs
When pb is pushed out
What is the high flow mode?
When pb is pushed in
Delivers 30 psi
HIGH caption illuminated in blue on the pb
What is the primary heat exchanger?
Located in a ram air duct in the landing gear fairing
Exhaust located on the bottom of the landing gear fairing, just forward of the landing gear
If there is insufficient airflow, a ground turbo fan will draw air from the ground inlet
When will the turbofan shut off valve automatically open?
when speed is less than or equal to 150 kt and landing gear extended or retracted for less than 10 minutes
Closed anytime the airspeed is greater than 150 kts as this produces sufficient airflow over heat exchanger
If an engine is experiencing low oil pressure, the turbo fan valve on the opposite side will automatically open
What does the compressor section do after the primary heat exchanger?
Increases the pressure and temperature of the partially cool bleed air
Then flows through a secondary heat exchanger for additional heat extraction
How is temperature control achieved?
Bleed air is mixed with the air produced by the expansion turbine
What does the temperature selector use to control the temperature when pb selected in?
- the temp selected on the selector
- the temp in the pack supply duct
- the aircraft skin temp
- associated compartment ambient temp
What is the temperature limit in manual mode?
88 degrees
If this is reached or exceeded, a limiter will gradually close the temp control valve to allow more air into the duct
When will you get an OVHT warning?
When the duct temp exceeds 92 degrees
Single chime
Master caution
AIR on CAP
When will the pack valve automatically close?
If the temp exceeds 204 degrees
When will the pack valve automatically close?
If the temp exceeds 204 degrees
What happens in the mixing chamber?
Mixes the air produced by the air conditioning pack with air drawn from the cabin
One mixing chamber per pack
What do the recirculation fans do?
Located in the under floor area just ahead of the wheel wells
Draw air through the floor vents and circulate air through the cabin while keeping the floor temp comfortable
Powered by the DC utility bus
Fan rotation speed depends on position of associated temp control valve - varies between 1500 and 2200 RPM
Will automatically run at full speed if temp is less than 18 degrees
When will you get a recirculation fan FAULT?
- fan speed less than 900 RPM
- associated electrical motor overheats
Where is ventilated using ambient air?
- flight deck
- forward cargo compartment
- electric and electronic equipment racks
Direction of air is controlled by two valves - under floor valve and overboard valve
How are the flight instruments cooled?
Air is drawn forward through the flight deck into ducting by an extract fan
Used to cool flight instruments, floor mounted batteries and electronics racks
When will the ventilation extract fan operate at high/low speeds?
Low speed - if temp is below 20 degrees
Full speed - if temp is above 52 degrees
Fan speed will vary with temp if it is between these two values
What is the purpose of the extract air flow lever?
Located on the right maintenance panel
Closes the extract air flow valve in order to stop air from flowing forward through the flight deck in case smoke is detected in the forward cargo compartment
What happens to the extract fan during engine start?
Will stop for 120 seconds to avoid pressure shocks
FAULT light on exhaust mode pb will illuminate
What does the overboard valve do?
Allows air to be discharged overboard
Controls the operation of the under floor valve
Overboard valve switch should be in the auto position to allow proper operation of the under floor valve
What happens if the exhaust mode pb is pushed in
Aicraf on ground and engine 1 has low oil pressure or is not running - overboard valve will be fully open and under floor valve fully closed and extract fan will run continuously
What happens if the aircraft is on the ground with number 1 engine running
Extract fan will run continuously, overboard valve fully closed and under floor valve fully open
How is pressurisation achieved?
- controlling the amount of air that is exhausted overboard
- cabin and flight deck pressurised through both the left and right packs
What are the outflow valves?
- control cabin pressurisation and cabin rate of change
- one electro-pneumatic valve and one pneumatic valve
- bottom aft portion of fuselage just forward of the aft entry door
What is the automatic mode?
The pneumatic valve slaved to the electro pneumatic valve by interconnected vacuum tube, which allows both valves to operate simultaneously
What pressure will the outflow valve open?
If cabin pressure differential exceeds 6.35 psi
If differential pressure exceeds 0.5 psi, a non-return line will open the outflow valve to relieve the negative pressure differential
What does the pressurisation controller use to calculate cabin elevation?
- departure field elevation
- destination field elevation
- existing cabin altitude
- aircraft flight altitude
Uses info from ADC 1 + captains altimeter
What happens if ADC 1 fails?
Pressurisation controller will use ADC 2 and a baro setting of 29.92
Crew will need to input the landing airport pressure altitude into the landing elevation window of the controller
What powers the electro-pneumatic valve?
Requires electrical power in order to operate
Loss of power or loss of signal from the pressurisation controller will cause the valve to close automatically
Powered by DC emer bus
How can you place the system in automatic mode?
When the MODE SEL button on the CAB PRESS panel is pressed in
MAN RATE knob must be in the NORM position
How is manual mode selected and indicated?
Releasing out the MODE pb
MAN caption illuminates in the pb
Digits in the landing elevation window will extinguish and the electro-pneumatic outflow valve close
What is manual mode?
MAN RATE knob is used to directly control the pneumatic outflow valve
Can select a rate of change from -1500 to +2500 FPM
MAN RATE knob should be set to 9 to 10 position to avoid a pressure bump when transitioning from auto to manual
What range of landing elevation can be set?
-1500 to +9900 feet in 100 foot increments
What is the maximum cabin rate of climb?
550 feet per minute
What is the maximum cabin differential pressure?
6 psi
What will be the cabin altitude if the aircraft is at FL250?
6740 ft
What is the max cabin rate of descent?
400 fpm
What does the pressurisation controller target in a descent?
Landing field elevation that was set during the pre flight, minus 300 ft
What is the max cabin rate of climb after touchdown?
550 fpm
What is the automatic return feature?
If you need to return to the departure airport after take off, pressurisation controller will use the departure airfield elevation minus 300 ft as target altitude for landing
Available until the aircraft climbs 3500 ft above departure airfield elevation
How can you change the maximum rate of descent?
By pressing the DESCENT RATE pb on the AUTO PRESS control panel
What will happen to the right pack valve after the pb is pressed?
It will open after a 6 sec delay for passenger comfort
When will the FAULT caption on the pack valve pb illuminate?
- associated pack valve position disagrees with the commanded position
- overheat downstream of the pack compressor (pack valve will be latched closed)
When should you not open the overboard valve?
If the differential pressure exceeds 1 psi
Opening the valve in flight could result in a depressurisation of the cabin and a possible collapse of the overboard duct
What is the position of the overboard/underfloor valves in flight?
Overboard valve will be partially open to allow differential pressure to provide necessary suction to provide cooling airflow in the compartments
Underfloor valve will be closed
Extract fan will be off
When will the exhaust mode pb FAULT light illuminate
- failure of extract fan
- fan overheat (more than 90 degrees)
When will the FAULT light illuminate on the avionics panel?
When the overboard valve is not in the commanded position
Will not illuminate if the overboard valve switch is in the FULL close position
- in ground with low oil pressure on eng 1 - if not full open
- on ground with eng 1 running/inflight - if the valve is fully open
When will the MODE SEL FAULT light illuminate?
In the event of a failure of the digital pressurisation controller
What does the DITCH position do?
Closes both outflow valves - two electric motors maintain them closed, powered by DC emer bus
Prevents water from entering the fuselage
What is the guarded dump pb used for?
To dump cabin pressure
When pressed, the digital pressurisation controller is disabled and electrical signal will fully open the electro-pneumatic valve and in turn the pneumatic valve
Only available in automatic mode
What is the indication of a successful test?
- alternating 18800 and -8800 in the landing elevation window
- FAULT on pressurisation mode pb
- test function inhibited in flight
What warning will you get if the cabin alt exceeds 10,000 ft?
- master warning
- CRC
- EXCESS ALT on CAP
What is the max differential pressure for landing?
0.35 psi
What is the max operating altitude with one bleed system operative?
20,000 ft
