Air Conditioning & Pressurization Flashcards
Where are the packs located
rear fuselage
or
behind the aft pressure dome
Where does bleed air come from into the AC packs
Engines or the APU
What two different air sources are mixed in the mixer manifold?
Temperature-controlled air from the AC pack and recirculated cabin air
and if required hot bleed air
Can conditioned air from an external ground source be used?
Yes
Where does Fwd pack supply air to?
Flight compartment
Where does Aft pack supply air to?
Cabin
If either pack fails how is air supplied to flight compartment and/or cabin?
The remaining pack will supply air to both
What is PRSOVs
Pressure regulator and shut off valves
If one PRSOV is closed what happens to airflow
Airflow is halved
What percentage of air is directed to the cabin and flight compartment?
70/30
How many recirc fans serve each AC pack
One per each pack
Where are recirc fans located?
Aft of the pressure dome
What does the avionics-cooling fan do?
Draws air out of the avionics rack and discharges it under the floor
How do you turn on the avionics-cooling fan?
It is operational whenever DC power is on
How do you know if the avionics-cooling fan failure is present?
Indicated on the annunciation on the forward flight attendants panel.
What regulates the temperature in automatic mode?
Automatic Temperature Contoller
How does the Automatic Temperature Controller regulate temperature?
It compares the temperature with that of the selected value.
Desired temp is selected on the Automatic Temperature Controller.
The selected and sensed temperature is processed in it’s associated Automatic Temperature Controller which then signals the Pack Temperature Control Valve.
The Pack Temperature Control Valve then establishes the mixture of regulated and recirculated air for the compartment.
How can you maintain temperature if a malfunction occurs in the Automatic Temperature Control system?
Using the manual temperature control switches
What happens to the temperature control valves if the cabin or flight compartment duct hot lights illuminate?
Associated temperature control valves are automatically commanded to the full cool position regardless of AUTO or MAN operation.
If over temperature condition persists in flight compartment or cabin ducts, what action should flight crew take?
Turn the associated pack OFF
How does pressurization system control the cabin altitude?
The Cabin Pressure Controller modulates the Aft automatic outflow valves located on the aft pressure dome.
The regulation of this discharge of air from the cabin is how the pressurization/cabin altitude is maintiained.
How do the aft outflow valves operate?
One is controlled electro-pneumatically and the other is pneumatically slaved to the first one.
How many outflow valves are present in the aircraft?
3 outflow valves; 2 aft, 1 fwd.
What is the fwd outflow valve used for?
manual pressurization control and smoke removal
In automatic pressurization modes, which inputs are received by the cabin altitude computer?
Cabin and ambient pressure sensors
Weight on Wheels switch
Power lever position
Cabin altitude sensor
On ground, when does the cabin altitude descend slightly below ambient?
When
- All doors are closed
- Air conditioning packs are selected ON
- One or more bleed valve ON
When power levers are advanced for take off, cabin altitude descends to 140 feet below ambient.
BLEED HOT caution
Wing leading edge duct temperature exceeds 290 degrees Celcius
associated nacelle shut-off valve closes
When over temp condition ceases, caution light extinguishes and normal system operation is restored
CABIN PACK HOT
or
FLT COMPT PACK HOT
Pack compressor discharge duct temperature exceeds 207 degrees Celcius.
associated PRSOV to the pack closes
When over temp condition ceases, caution light extinguishes and normal system operation is restored
CABIN DUCT HOT
or
FLT COMPT DUCT HOT
Duct temperature exceeds 88 degrees Celcius.
associated pack temperature control valves are commanded to full cool position.
When temperature drops to 82 degrees Celcius, caution light extinguishes.
If caution light remains for over 20 seconds, pack temperature control valve may be faulty and pack should be shut down
What happens in electrical failure
HP shut-off valves are de-energized to prevent thermal any thermal hazard from the hot HP bleed air
PRSOVs must be energized to close and thus remain open (electrical failure so cannot be energized). In this case LP bleed air is allowed into the air conditioning system for temperature control and cabin pressurization.
When is ram air let in for ventilation?
When both air conditioning packs fail
Where is ram air duct located?
In the dorsal fin
How would you initiate full ventilation throughout the cabin and flight compartment
Turn the forward outflow valve selector clockwise 90 degrees
This opens the valve to ambient
When is manual pressurization used?
In the event of a loss of electrical power or a malfunction occurs in the automatic pressurization system which leads to the cabin pressure difference to exceed maximum pressure differential limits
What does selecting the MAN mode for pressurization do to the pressurization computer and aft outflow valves?
The pressurization computer is deactivated and the aft outflow valves are closed
What can you expect when you select MAN mode and the aft outflow valves close?
Cabin altitude decreases rapidly
Can the manual system be used with the automatic system functioning?
Yes.
What does selecting DUMP do to the aft outflow valves?
Opens them, preventing pressurization
