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