Air Conditioning & Pressurization

Question 1

Where are the packs located

Answer 1

rear fuselage
or
behind the aft pressure dome

Question 2

Where does bleed air come from into the AC packs

Answer 2

Engines or the APU

Question 3

What two different air sources are mixed in the mixer manifold?

Answer 3

Temperature-controlled air from the AC pack and recirculated cabin air
and if required hot bleed air

Question 4

Can conditioned air from an external ground source be used?

Answer 4

Yes

Question 5

Where does Fwd pack supply air to?

Answer 5

Flight compartment

Question 6

Where does Aft pack supply air to?

Answer 6

Cabin

Question 7

If either pack fails how is air supplied to flight compartment and/or cabin?

Answer 7

The remaining pack will supply air to both

Question 8

What is PRSOVs

Answer 8

Pressure regulator and shut off valves

Question 9

If one PRSOV is closed what happens to airflow

Answer 9

Airflow is halved

Question 10

What percentage of air is directed to the cabin and flight compartment?

Answer 10

70/30

Question 11

How many recirc fans serve each AC pack

Answer 11

One per each pack

Question 12

Where are recirc fans located?

Answer 12

Aft of the pressure dome

Question 13

What does the avionics-cooling fan do?

Answer 13

Draws air out of the avionics rack and discharges it under the floor

Question 14

How do you turn on the avionics-cooling fan?

Answer 14

It is operational whenever DC power is on

Question 15

How do you know if the avionics-cooling fan failure is present?

Answer 15

Indicated on the annunciation on the forward flight attendants panel.

Question 16

What regulates the temperature in automatic mode?

Answer 16

Automatic Temperature Contoller

Question 17

How does the Automatic Temperature Controller regulate temperature?

Answer 17

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.

Question 18

How can you maintain temperature if a malfunction occurs in the Automatic Temperature Control system?

Answer 18

Using the manual temperature control switches

Question 19

What happens to the temperature control valves if the cabin or flight compartment duct hot lights illuminate?

Answer 19

Associated temperature control valves are automatically commanded to the full cool position regardless of AUTO or MAN operation.

Question 20

If over temperature condition persists in flight compartment or cabin ducts, what action should flight crew take?

Answer 20

Turn the associated pack OFF

Question 21

How does pressurization system control the cabin altitude?

Answer 21

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.

Question 22

How do the aft outflow valves operate?

Answer 22

One is controlled electro-pneumatically and the other is pneumatically slaved to the first one.

Question 23

How many outflow valves are present in the aircraft?

Answer 23

3 outflow valves; 2 aft, 1 fwd.

Question 24

What is the fwd outflow valve used for?

Answer 24

manual pressurization control and smoke removal

Question 25

In automatic pressurization modes, which inputs are received by the cabin altitude computer?

Answer 25

Cabin and ambient pressure sensors Weight on Wheels switch Power lever position Cabin altitude sensor

Question 26

On ground, when does the cabin altitude descend slightly below ambient?

Answer 26

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.

Question 27

BLEED HOT caution

Answer 27

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

Question 28

CABIN PACK HOT or FLT COMPT PACK HOT

Answer 28

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

Question 29

CABIN DUCT HOT or FLT COMPT DUCT HOT

Answer 29

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

Question 30

What happens in electrical failure

Answer 30

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.

Question 31

When is ram air let in for ventilation?

Answer 31

When both air conditioning packs fail

Question 32

Where is ram air duct located?

Answer 32

In the dorsal fin

Question 33

How would you initiate full ventilation throughout the cabin and flight compartment

Answer 33

Turn the forward outflow valve selector clockwise 90 degrees | This opens the valve to ambient

Question 34

When is manual pressurization used?

Answer 34

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

Question 35

What does selecting the MAN mode for pressurization do to the pressurization computer and aft outflow valves?

Answer 35

The pressurization computer is deactivated and the aft outflow valves are closed

Question 36

What can you expect when you select MAN mode and the aft outflow valves close?

Answer 36

Cabin altitude decreases rapidly

Question 37

Can the manual system be used with the automatic system functioning?

Answer 37

Yes.

Question 38

What does selecting DUMP do to the aft outflow valves?

Answer 38

Opens them, preventing pressurization