B737-300/400 Air systems

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737-300/400737-300/400AIR SYSTEMSAIR SYSTEMS

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737-300/400 Pneumatic Schematic

Air Mix Manifold

To cowlTo cowlanti-iceanti-ice

99thth stage stageairair

55thth stage air stage air




9th stage modulating and shutoff

valve


valve

Pre-cooler Pre-cooler (fan air)(fan air)

To starterTo starter

Bleedvalve

Overboard

P T

Pre-cooler

T

Pre-cooler temp sensor

Start valveTo wing

anti-ice

T P

Bleedvalve

T


Overboard

Pre-coolerPre-cooler Pre-cooler

(fan air)(fan air)

To starterTo starter

To wing anti-ice Start valve

Deflector door

Ram air inlet

Turbofan valve Turbofan

LeftPACKvalve

To hydraulicreservoir

(“A” & “B”)

P

TurbofanTurbofan

valve

RightPACKvalve

Ram airexhaust louvers



(“A” & “B”)

Isolation valve

Deflector door

P

T

T

Riser to flight deck

From forward cargo compartment shroud

Recircfan

Ground air conditioning

To cabin (left sidewall riser)

TSupplyduct temp

To cabin (right sidewall riser)

T

T

Left ductpressure

Right ductpressure

T T

Right PACK

Cold Hot

Waterseparator

Air mixvalves

Left PACK

T T

ColdHot

Waterseparator

Air mixvalves

Towatertank

Ram air inlet door

Ram air inlet

Ram air inlet door

Ground pneumatic air(air start cart)

APUbleedvalve

APU

No. 1 engine No. 2 engine



No. 1 engine

The No. 1 engine supplies either 5th or 9th stage bleed air to the pneumatic manifold.

Bleed air from the 5th stage is normally utilized, while 9th

stage bleed air is utilized when the engine rpm is low.


Bleedvalve


valve




The engine anti-ice plumbing is prior to the engine bleed valve.

Therefore, engine anti-ice is available regardless of the position of the bleed valve

(open or closed).

No. 1 engine


Bleedvalve


valve





The left BLEED TRIP OFF light illuminates whenever the No. 1 engine pressure or temperature exceeds a predetermined limit, which in turn will automatically

close the bleed valve.

No. 1 engine


Bleedvalve


valve



P T



The pre-cooler temp sensor measures the temperature of the bleed air. If needed, it will

send an electrical signal to open the pre-cooler valve

which then allows fan air to cool the bleed air.

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




Bleed air is required to start an engine. This air may originate

from the APU, a ground source, or the other engine.

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T


To starterTo starterStart valve



Bleed air from the No. 1 engine is normally utilized for left wing

anti-ice. If bleed air from the No. 1 engine is not available,

bleed air from the No. 2 engine may be utilized if the isolation

valve is open.

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T



PLeft ductpressure Isolation valve

To left wing anti-ice



Pneumatic pressure for both “A” and “B” hydraulic

reservoirs may be taken from the left side of the pneumatic

manifold.


(“A” & “B”)

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)




T




APU bleed air enters the pneumatic manifold on the left

side of the isolation valve.

APUbleedvalve

APU

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T





(“A” & “B”)




Bleed air to the left Pressure and Air Conditioning Kit

(PACK) normally originates from the No. 1 engine. If the No. 1 engine bleed air is not

available, APU bleed air may be utilized.

Left PACK

LeftPACKvalve

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU


(“A” & “B”)




The air cycle machine (inside the PACK bay) consists of a compressor and a turbine. Its function is to assist in

cooling the bleed air. A temperature sensor measures bleed air exiting the compressor and a temperature sensor

measures bleed air entering the turbine. Either one of these sensors will illuminate

the PACK TRIP OFF light if the predetermined temperature is exceeded.

Left PACK

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve


(“A” & “B”)


T T



Ram air is also utilized to cool the bleed air. This is done via

two heat exchangers located in the PACK bay. When

necessary, the turbofan helps draw ram air into the system.

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve


(“A” & “B”)




The turbofan operates utilizing bleed air.

Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve


(“A” & “B”)




As the conditioned air exits the left PACK, it then enters the air

mix manifold where it combines with conditioned air from the right PACK. The air then travels into the cabin via

the left and right sidewall risers.

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve


(“A” & “B”)


ColdHot

Waterseparator

Air mixvalves



Some of the conditioned air from the left PACK is routed to

the flight deck. In this plumbing there are two

temperature sensors: one for the PACK TRIP OFF light and

one for the DUCT OVERHEAT light.


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)




The recirculation fan (RECIRC FAN) draws air from a shroud

above the forward cargo compartment and directs it

back into the air mix manifold. From there it is recirculated

back into the cabin

From shroud above forward cargo compartment

Recircfan


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)




The ground air conditioning hose is connected directly to

the air mix manifold, where it is then routed to the cabin via the

sidewall risers. Air from this hose is not processed by either

PACK.



T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan




The potable water tank has a capacity of approximately 20

U.S. gallons and is pressurized from the left side of the

pneumatic manifold.

Towatertank


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan





The No. 2 engine supplies either 5th or 9th stage bleed air to the pneumatic manifold.

Bleed air from the 5th stage is normally utilized, while 9th

stage bleed air is utilized when the engine rpm is low.

No. 2 engine


Bleedvalve



valve


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan



Towatertank



The engine anti-ice plumbing is prior to the engine bleed valve.

Therefore, engine anti-ice is available regardless of the position of the bleed valve

(open or closed).


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve

Towatertank





The right BLEED TRIP OFF light illuminates whenever the

No. 2 engine pressure or temperature exceeds a

predetermined limit, which in turn will automatically close

the bleed valve.


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


Towatertank


T P


737-300/400 Pneumatic SchematicRiser to flight

deck

T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


T PTo

watertank


The pre-cooler temp sensor measures the temperature of the bleed air. If needed, it will

send an electrical signal to open the pre-cooler valve

which then allows fan air to cool the bleed air.

Overboard


(fan air)(fan air)

T




Bleed air is required to start an engine. This air may originate

from the APU, a ground source, or the other engine.


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


T P

Overboard


(fan air)(fan air)

T


Towatertank





Bleed air from the No. 2 engine is normally utilized for right

wing anti-ice. If bleed air from the No. 2 engine is not

available, bleed air from the No. 1 engine may be utilized if the

isolation valve is open.

P

Right ductpressure

To right wing anti-ice


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


T P

Overboard


(fan air)(fan air)

T



Towatertank




Pneumatic pressure for both “A” and “B” hydraulic

reservoirs may be taken from the right side of the pneumatic

manifold.


(“A” & “B”)

P

Right ductpressure


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


T P

Overboard


(fan air)(fan air)

T



Towatertank





Bleed air to the right PACK normally originates from the

No. 2 engine. If the No. 2 engine bleed air is not

available, APU bleed air may be utilized if the isolation valve is

open.

Right PACK

RightPACKvalve

P

Right ductpressure


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


T P

Overboard


(fan air)(fan air)

T




(“A” & “B”)

Towatertank





The air cycle machine (inside the PACK bay) consists of a compressor and a turbine. Its function is to assist in cooling the bleed air. A temperature sensor measures bleed air exiting the compressor and a temperature sensor

measures bleed air entering the turbine. Either one of these sensors will illuminate the PACK TRIP OFF

light if the predetermined temperature is exceeded.

P

Right ductpressure


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


T P

Overboard


(fan air)(fan air)

T




(“A” & “B”)

Right PACK

RightPACKvalve

Towatertank



T T



Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Ram air is also utilized to cool the bleed air. This is done via

two heat exchangers located in the PACK bay. When

necessary, the turbofan helps draw ram air into the system.

P

Right ductpressure


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


T P

Overboard


(fan air)(fan air)

T




(“A” & “B”)

Right PACK

RightPACKvalve

T T

Towatertank





The turbofan operates utilizing bleed air.

Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door

P

Right ductpressure


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


T P

Overboard


(fan air)(fan air)

T




(“A” & “B”)

Right PACK

RightPACKvalve

T T

Turbofan


Towatertank





As the conditioned air exits the right PACK, it then enters the

air mix manifold where it combines with conditioned air

from the left PACK. The air then travels into the cabin via

the left and right sidewall risers.

Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door

P

Right ductpressure


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


T P

Overboard


(fan air)(fan air)

T




(“A” & “B”)

Right PACK

RightPACKvalve

T T

Turbofan


Towatertank



Cold Hot

Waterseparator

Air mixvalves



In the right sidewall riser plumbing there are two

temperature sensors: one for the PACK TRIP OFF light and

one for the DUCT OVERHEAT light.

Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door

P

Right ductpressure


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


T P

Overboard


(fan air)(fan air)

T




(“A” & “B”)

Right PACK

RightPACKvalve

T T

Turbofan


Cold Hot

Waterseparator

Air mixvalves

Towatertank



T

T



If necessary, ground pneumatic air may be connected to the aircraft to start an engine or

operate either PACK.

Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door

P

Right ductpressure


T

T

Air Mix Manifold


TSupplyduct temp


Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Left PACK

T T

No. 1 engine


Bleedvalve


valve



P T

Overboard


(fan air)(fan air)

T




APUbleedvalve

APU

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves


(“A” & “B”)


Recircfan


No. 2 engine


Bleedvalve



valve


T P

Overboard


(fan air)(fan air)

T




(“A” & “B”)

Right PACK

RightPACKvalve

T T

Turbofan


Cold Hot

Waterseparator

Air mixvalves

T

T

Towatertank



This concludes the review of the Pneumatic Schematic. The next section This concludes the review of the Pneumatic Schematic. The next section will discuss Bleed Air/Air Conditioning Controls and Indicators. Click will discuss Bleed Air/Air Conditioning Controls and Indicators. Click NextNext to continue. to continue.



Bleed Air/400 and Air ConditioningBleed Air/400 and Air Conditioning Controls and IndicatorsControls and Indicators

Forward Overhead PanelForward Overhead Panel


Bleed Air and Air ConditioningBleed Air and Air Conditioning Controls and IndicatorsControls and Indicators

DUAL BLEED Light:DUAL BLEED Light:Illuminated –Illuminated –Indicates that the potential of back-pressuring the Indicates that the potential of back-pressuring the APU exists. APU exists.

The following scenarios will result in illumination The following scenarios will result in illumination of the DUAL BLEED light:of the DUAL BLEED light:• No. 1 engine bleed air No. 1 engine bleed air switchswitch ON and APU bleed ON and APU bleed

air air valvevalve open. open.• No. 2 engine bleed air No. 2 engine bleed air switchswitch ON, APU bleed air ON, APU bleed air

valvevalve open, and isolation open, and isolation valvevalve open. open.



RAM DOOR FULL OPEN lights:RAM DOOR FULL OPEN lights:Illuminated –Illuminated –Respective ram air inlet door is in the full-open Respective ram air inlet door is in the full-open position.position.

See picture of See picture of left ram air inlet doorleft ram air inlet door

See picture of See picture of right ram air inlet doorright ram air inlet door



RECIRC FAN Switch:RECIRC FAN Switch:AUTO –AUTO –The recirculation fan is signaled to operate. The The recirculation fan is signaled to operate. The recirculation fan will recirculation fan will not operatenot operate if both PACK’s if both PACK’s are operating are operating andand either PACK switch is either PACK switch is positioned to HIGH.positioned to HIGH.

OFF –OFF –The recirculation fan is signaled OFF.The recirculation fan is signaled OFF.



Bleed Air Duct Pressure Indicator:Bleed Air Duct Pressure Indicator:• Indicates the pressure (psi) in the left and right Indicates the pressure (psi) in the left and right

pneumatic manifold.pneumatic manifold.• Two needles, “L” and “R”.Two needles, “L” and “R”.



Wing-Body OVHT TEST Switch:Wing-Body OVHT TEST Switch:Push –Push –• Tests the circuits for the wing-body overheat Tests the circuits for the wing-body overheat

system.system.• Illuminates both WING-BODY OVERHEAT lights.Illuminates both WING-BODY OVERHEAT lights.• Test may take up to five seconds to complete.Test may take up to five seconds to complete.



Air Conditioning PACK Switches (Left and Right):Air Conditioning PACK Switches (Left and Right):OFF –OFF –Respective PACK signaled OFF (PACK valve closes).Respective PACK signaled OFF (PACK valve closes).

AUTO –AUTO –• With both PACK’s operating, each PACK With both PACK’s operating, each PACK

regulates to the “low flow” mode (55 pounds/min.).regulates to the “low flow” mode (55 pounds/min.).• With only one PACK operating (in flight with With only one PACK operating (in flight with

trailing edge flaps “up”), the operating PACK trailing edge flaps “up”), the operating PACK regulates to the “high flow” mode (80 pounds/min.).regulates to the “high flow” mode (80 pounds/min.).• When only one PACK is operating and utilizing When only one PACK is operating and utilizing

the APU as the bleed air source (both engine bleed the APU as the bleed air source (both engine bleed air switches OFF), the operating PACK regulates to air switches OFF), the operating PACK regulates to the “high flow” mode (80 pounds/min.).the “high flow” mode (80 pounds/min.).

HIGH –HIGH –• Respective PACK regulates to the “high flow” mode Respective PACK regulates to the “high flow” mode

(80 pounds/min.).(80 pounds/min.).• While on the ground and operating one PACK with While on the ground and operating one PACK with

APU bleed air, the operating PACK regulates to the APU bleed air, the operating PACK regulates to the “APU high air flow” mode (100 pounds/min.). “APU high air flow” mode (100 pounds/min.).



ISOLATION VALVE Switch:ISOLATION VALVE Switch:CLOSE –CLOSE –Closes isolation valve.Closes isolation valve.

AUTO –AUTO –• Isolation valve will Isolation valve will closeclose if both BLEED switches if both BLEED switches

are positioned to ON and both PACK switches are are positioned to ON and both PACK switches are positioned to either AUTO or HIGH.positioned to either AUTO or HIGH.• Isolation valve will automatically Isolation valve will automatically openopen if any one of if any one of

the “four corner” switches (BLEED or PACK) are the “four corner” switches (BLEED or PACK) are positioned to OFF.positioned to OFF.

OPEN –OPEN –Opens isolation valve. Opens isolation valve.



Engine BLEED Air Switches (labeled “1” and “2”):Engine BLEED Air Switches (labeled “1” and “2”):OFF –OFF –Closes respective engine bleed air valve.Closes respective engine bleed air valve.

ON –ON –Opens respective engine bleed air valve when Opens respective engine bleed air valve when related engine is operating. related engine is operating.

Note: The engine bleed air valves are electrically Note: The engine bleed air valves are electrically activated and pneumatically operated, therefore activated and pneumatically operated, therefore bleed air from the respective engine is required for bleed air from the respective engine is required for the valve to remain open.the valve to remain open.



APU BLEED Air Switch:APU BLEED Air Switch:OFF –OFF –Closes APU bleed air valve.Closes APU bleed air valve.

ON –ON –Opens APU bleed air valve when APU is operating. Opens APU bleed air valve when APU is operating.

Note: The APU bleed air valve is electrically Note: The APU bleed air valve is electrically activated and pneumatically operated, therefore activated and pneumatically operated, therefore bleed air from the APU is required for the valve to bleed air from the APU is required for the valve to remain open.remain open.



PACK TRIP OFF Lights:PACK TRIP OFF Lights:Illuminated –Illuminated –• Respective PACK temperature or respective Respective PACK temperature or respective supply supply duct has duct has exceeded limits.exceeded limits.• Respective PACK valve automatically closes and Respective PACK valve automatically closes and

air mix valves drive to the “full-cold” position. air mix valves drive to the “full-cold” position.

Note: To reset (extinguish) the PACK TRIP OFF light Note: To reset (extinguish) the PACK TRIP OFF light and regain control of the PACK valve, the TRIP and regain control of the PACK valve, the TRIP RESET switch must be pushed.RESET switch must be pushed.

Note: The “full-cold” position of the air mix valves Note: The “full-cold” position of the air mix valves is defined as the cold air mix valve being full-open is defined as the cold air mix valve being full-open and the hot air mix valve being full-closed. and the hot air mix valve being full-closed.



WING-BODY OVERHEAT Lights:WING-BODY OVERHEAT Lights:Illuminated –Illuminated –• Left light indicates a bleed air duct leak in the left Left light indicates a bleed air duct leak in the left

pneumatic manifold.pneumatic manifold.• Right light indicates a bleed air duct leak in the Right light indicates a bleed air duct leak in the

right pneumatic manifold.right pneumatic manifold.



BLEED TRIP OFF Lights:BLEED TRIP OFF Lights:Illuminated –Illuminated –• Excessive bleed air temperature or pressure from Excessive bleed air temperature or pressure from

respective engine.respective engine.• Respective engine bleed air valve automatically Respective engine bleed air valve automatically

closes.closes.

Note: To reset (extinguish) the BLEED TRIP OFF Note: To reset (extinguish) the BLEED TRIP OFF light and regain control of the bleed valve, the TRIP light and regain control of the bleed valve, the TRIP RESET switch must be pushed.RESET switch must be pushed.



TRIP RESET Switch:TRIP RESET Switch:Push –Push –Will reset (extinguish) PACK TRIP OFF, BLEED TRIP Will reset (extinguish) PACK TRIP OFF, BLEED TRIP OFF and DUCT OVERHEAT lights, if condition that OFF and DUCT OVERHEAT lights, if condition that initiated the fault has been corrected.initiated the fault has been corrected.

Note: Lights remain illuminated until reset.Note: Lights remain illuminated until reset.



AIR TEMP Source Selector:AIR TEMP Source Selector:SUPPLY DUCT –SUPPLY DUCT –Selects the main distribution supply duct sensor. Selects the main distribution supply duct sensor. Air temperature at the sensor is then displayed on Air temperature at the sensor is then displayed on the air temperature indicator.the air temperature indicator.

Note: This sensor is located in the flight deck aft of Note: This sensor is located in the flight deck aft of the aft overhead panel.the aft overhead panel.

PASS CABIN –PASS CABIN –Selects passenger cabin sensor. Air temperature at Selects passenger cabin sensor. Air temperature at the sensor is then displayed on the air temperature the sensor is then displayed on the air temperature indicator.indicator.

Note: This sensor is located in the forward half of Note: This sensor is located in the forward half of the passenger cabin, aircraft right, on the underside the passenger cabin, aircraft right, on the underside of one of the overhead stowage compartments.of one of the overhead stowage compartments.



AIR MIX VALVE Indicators:AIR MIX VALVE Indicators:• Indicates position of the air mix valves (left Indicates position of the air mix valves (left

indicator is for the left PACK air mix valves; right indicator is for the left PACK air mix valves; right indicator is for the right PACK air mix valves).indicator is for the right PACK air mix valves).• Controlled automatically when the respective Controlled automatically when the respective

temperature selector is in AUTO.temperature selector is in AUTO.• Controlled manually when the respective Controlled manually when the respective temperature selector positioned to MANUAL.temperature selector positioned to MANUAL.



TEMP (Air Temperature) Indicator:TEMP (Air Temperature) Indicator:Indicates temperature at location selected by the Indicates temperature at location selected by the AIR TEMP source selector.AIR TEMP source selector.



DUCT OVERHEAT Lights:DUCT OVERHEAT Lights:Illuminated –Illuminated –• Bleed air in respective duct exceeds limits (left Bleed air in respective duct exceeds limits (left

DUCT OVERHEAT sensor located in the supply DUCT OVERHEAT sensor located in the supply duct leading to the flight deck; right DUCT duct leading to the flight deck; right DUCT OVERHEAT sensor located in the right sidewall OVERHEAT sensor located in the right sidewall riser leading to the passenger cabin).riser leading to the passenger cabin).• Respective PACK air mix valves drive to the Respective PACK air mix valves drive to the

“full-cold” position.“full-cold” position.

Note: To reset (extinguish) the DUCT OVERHEAT Note: To reset (extinguish) the DUCT OVERHEAT light and regain control of the air mix valves, the light and regain control of the air mix valves, the TRIP RESET switch must be pushed. TRIP RESET switch must be pushed.

Note: The “full-cold” position of the air mix valves Note: The “full-cold” position of the air mix valves is defined as the cold air mix valve being full-open is defined as the cold air mix valve being full-open and the hot air mix valve being full-closed.and the hot air mix valve being full-closed.



CONT CABIN & PASS CABIN Temperature Selectors: CONT CABIN & PASS CABIN Temperature Selectors: Two modes (AUTO & MANUAL) –Two modes (AUTO & MANUAL) –AUTO –AUTO –Left temperature selector allows an automatic Left temperature selector allows an automatic temperature controller to control the temperature of temperature controller to control the temperature of the control cabin (flight deck). Right temperature the control cabin (flight deck). Right temperature selector allows an automatic temperature controller selector allows an automatic temperature controller to control the temperature of the passenger cabin. to control the temperature of the passenger cabin.

MANUAL –MANUAL –The automatic temperature controller is bypassed The automatic temperature controller is bypassed and the air mix valves are now manually controlled.and the air mix valves are now manually controlled.

This concludes the review of the Bleed Air/Air Conditioning Controls and Indicators.This concludes the review of the Bleed Air/Air Conditioning Controls and Indicators.The next section will discuss the Cabin Pressurization Panel and various other panels.The next section will discuss the Cabin Pressurization Panel and various other panels.

Click Click NextNext to continue. to continue.


Cabin Pressurization PanelCabin Pressurization PanelControls and IndicatorsControls and Indicators




AUTO FAIL Light:AUTO FAIL Light:Illuminated –Illuminated –• Automatic pressurization control failure due to any Automatic pressurization control failure due to any

one of the following three conditions:one of the following three conditions: Loss of AC power for more than 15 secondsLoss of AC power for more than 15 seconds Excessive rate of cabin pressure change Excessive rate of cabin pressure change (+/- (+/- 1800 feet/min.)1800 feet/min.) Cabin altitude in excess of 13,875 feetCabin altitude in excess of 13,875 feet

• Control of pressurization automatically transfers to Control of pressurization automatically transfers to STANDBY mode.STANDBY mode.



OFF SCHED DESCENT Light:OFF SCHED DESCENT Light:Illuminated –Illuminated –Aircraft descends before reaching within 0.25 psi of Aircraft descends before reaching within 0.25 psi of the altitude which has been set in the FLT ALT the altitude which has been set in the FLT ALT indicator.indicator.



STANDBY Light:STANDBY Light:Illuminated –Illuminated –Pressurization system operating in the STANDBY Pressurization system operating in the STANDBY mode.mode.



MANUAL Light:MANUAL Light:Illuminated –Illuminated –Pressurization system operating in the MANUAL Pressurization system operating in the MANUAL mode.mode.



FLT ALT Indicator:FLT ALT Indicator:• Indicates selected cruise altitude.Indicates selected cruise altitude.• Selected cruise altitude is set prior to takeoff.Selected cruise altitude is set prior to takeoff.



FLT ALT Selector:FLT ALT Selector:Push and rotate to set planned cruise altitude in Push and rotate to set planned cruise altitude in FLT ALT indicator.FLT ALT indicator.

Note: If the flight altitude selector is depressed Note: If the flight altitude selector is depressed during the climb when operating in the AUTO mode, during the climb when operating in the AUTO mode, the automatic abort capability to the takeoff field the automatic abort capability to the takeoff field elevation will be lost.elevation will be lost.



LAND ALT Indicator:LAND ALT Indicator:• Indicates field elevation of the airport of intended Indicates field elevation of the airport of intended

landing.landing.• Field elevation of the airport of intended landing is Field elevation of the airport of intended landing is

set prior to takeoff.set prior to takeoff.



LAND ALT Selector:LAND ALT Selector:• Rotate to set field elevation of airport of intended Rotate to set field elevation of airport of intended

landing in LAND ALT indicator.landing in LAND ALT indicator.• Large diameter control sets 1000 foot increments.Large diameter control sets 1000 foot increments.• Small diameter control sets 10 foot increments.Small diameter control sets 10 foot increments.



CABIN RATE Selector:CABIN RATE Selector:DECR – DECR – Cabin altitude rate of change equals 50 feet/min.Cabin altitude rate of change equals 50 feet/min.

Index – Index – Cabin altitude rate of change equals 300 feet/min.Cabin altitude rate of change equals 300 feet/min.

INCR – INCR – Cabin altitude rate of change equals 2000 feet/min.Cabin altitude rate of change equals 2000 feet/min.

Note: Operates only with the pressurization mode Note: Operates only with the pressurization mode selector in STBY.selector in STBY.



CAB ALT Indicator:CAB ALT Indicator:• Indicates selected cabin altitude. Indicates selected cabin altitude. • Utilized when operating in the STANDBY mode.Utilized when operating in the STANDBY mode.



CAB ALT Selector:CAB ALT Selector:• Rotate to select desired cabin altitude.Rotate to select desired cabin altitude.• Large diameter control sets 1000 foot increments.Large diameter control sets 1000 foot increments.• Small diameter control sets 10 foot increments.Small diameter control sets 10 foot increments.



Main outflow VALVE Position Indicator:Main outflow VALVE Position Indicator:• Indicates position of main outflow valve.Indicates position of main outflow valve.• Operates in all three modes (AUTO, STANDBY, and Operates in all three modes (AUTO, STANDBY, and

MANUAL).MANUAL).



Main Outflow Valve Switch:Main Outflow Valve Switch:(spring-loaded to center)(spring-loaded to center)CLOSE –CLOSE –Closes main outflow valve electrically when the Closes main outflow valve electrically when the pressurization mode selector is in the MAN AC or pressurization mode selector is in the MAN AC or MAN DC position.MAN DC position.

OPEN –OPEN –Opens main outflow valve electrically when the Opens main outflow valve electrically when the pressurization mode selector is in the MAN AC or pressurization mode selector is in the MAN AC or MAN DC position.MAN DC position.



FLT/GRD Switch:FLT/GRD Switch:AUTO Mode –AUTO Mode –• GRD –GRD –

On the ground, drives the main outflow valve to the full-On the ground, drives the main outflow valve to the full-open position at a controlled rate and depressurizes the open position at a controlled rate and depressurizes the aircraft. After takeoff, switch is inhibited; function is the aircraft. After takeoff, switch is inhibited; function is the same as FLT position.same as FLT position.

• FLT –FLT –On the ground, pressurizes cabin to approximately 200 feet On the ground, pressurizes cabin to approximately 200 feet below takeoff field elevation. After takeoff, cabin pressure below takeoff field elevation. After takeoff, cabin pressure

is is automatically controlled in both the climb and automatically controlled in both the climb and decent phase decent phase as a function of airplane altitude. In as a function of airplane altitude. In the cruise phase, cabin the cruise phase, cabin pressure is held constant.pressure is held constant.

STANDBY Mode –STANDBY Mode –• GRD –GRD –

On the ground, drives the main outflow valve open at the On the ground, drives the main outflow valve open at the rate selected by the cabin rate selector. After takeoff, rate selected by the cabin rate selector. After takeoff,

switch switch is inhibited; function is the same as FLT position.is inhibited; function is the same as FLT position.

• FLT –FLT –Pressurizes the aircraft to the cabin altitude selected in the Pressurizes the aircraft to the cabin altitude selected in the cabin altitude indicator at the rate selected by the cabin rate cabin altitude indicator at the rate selected by the cabin rate selector.selector.



Pressurization Mode Selector:Pressurization Mode Selector:AUTO –AUTO –Pressurization system is controlled automatically.Pressurization system is controlled automatically.

STBY –STBY –Pressurization system is controlled utilizing the Pressurization system is controlled utilizing the STANDBY mode.STANDBY mode.

MAN AC –MAN AC –Pressurization system is controlled manually by the Pressurization system is controlled manually by the main outflow valve switch. Main outflow valve main outflow valve switch. Main outflow valve operates utilizing AC power. All auto and standby operates utilizing AC power. All auto and standby circuits are bypassed.circuits are bypassed.

MAN DC –MAN DC –Pressurization system is controlled manually by the Pressurization system is controlled manually by the main outflow valve switch. Main outflow valve main outflow valve switch. Main outflow valve operates utilizing DC power. All auto and standby operates utilizing DC power. All auto and standby circuits are bypassed.circuits are bypassed.

CHECK –CHECK –Tests auto failure function of the AUTO system.Tests auto failure function of the AUTO system.



Cabin/Flight Altitude Placard:Cabin/Flight Altitude Placard:Used to determine the setting for cabin altitude Used to determine the setting for cabin altitude (CAB ALT) when operating in the STANDBY and (CAB ALT) when operating in the STANDBY and MANUAL modes.MANUAL modes.



Cabin Altitude PanelCabin Altitude Panel


Cabin Altitude PanelCabin Altitude PanelCABIN ALT/DIFF PRESS Indicator:CABIN ALT/DIFF PRESS Indicator:Inner Scale (small white needle) –Inner Scale (small white needle) –Indicates cabin altitude in feet.Indicates cabin altitude in feet.

Outer Scale (large white needle) – Outer Scale (large white needle) – Indicates the difference between cabin pressure and Indicates the difference between cabin pressure and ambient pressure in psi (differential pressure).ambient pressure in psi (differential pressure).


Cabin Altitude PanelCabin Altitude PanelCABIN CLIMB Indicator:CABIN CLIMB Indicator:Indicates cabin rate of climb in feet/min.Indicates cabin rate of climb in feet/min.


Cabin Altitude PanelCabin Altitude Panel

Listen to the cabinListen to the cabinaltitude warning hornaltitude warning horn

ALT HORN CUTOUT:ALT HORN CUTOUT:Push –Push –Silences the intermittent cabin altitude warning horn.Silences the intermittent cabin altitude warning horn.

Note: Altitude warning horn sounds when the cabin Note: Altitude warning horn sounds when the cabin altitude reaches 10,000 feet. To reset this warning altitude reaches 10,000 feet. To reset this warning system, cabin must be brought back below system, cabin must be brought back below 10,000 feet.10,000 feet.

Note: The sound of the cabin altitude warning horn Note: The sound of the cabin altitude warning horn is the same sound as the takeoff configuration is the same sound as the takeoff configuration warning horn.warning horn.


Equipment Cooling PanelEquipment Cooling Panel



Equipment Cooling PanelEquipment Cooling PanelEQUIP COOLING Fan:EQUIP COOLING Fan:NORMAL –NORMAL –Normal cooling exhaust fan is activated. Normal cooling exhaust fan is activated.

ALTERNATE –ALTERNATE –Alternate cooling exhaust fan is activated.Alternate cooling exhaust fan is activated.

Note: Both cooling exhaust fans are located in the Note: Both cooling exhaust fans are located in the equipment and electronics (E&E) bay.equipment and electronics (E&E) bay.


Equipment Cooling PanelEquipment Cooling PanelEQUIP COOLING Fan OFF Light:EQUIP COOLING Fan OFF Light:Illuminated –Illuminated –No airflow from selected (normal or alternate) No airflow from selected (normal or alternate) cooling fan.cooling fan.

Note: If the OFF light illuminates when the aircraft is Note: If the OFF light illuminates when the aircraft is on the ground with one or both IRU’s powered, the on the ground with one or both IRU’s powered, the crew call horn (located in the nose wheel well) will crew call horn (located in the nose wheel well) will sound after a 19 second delay. This is to alert the sound after a 19 second delay. This is to alert the ground crew of an impending overheat condition in ground crew of an impending overheat condition in the IRU(s). The horn will sound until airflow is the IRU(s). The horn will sound until airflow is restored. restored.

This concludes the review of Air System Panels. The remainderThis concludes the review of Air System Panels. The remainderof the presentation will discuss the air system in greater detail.of the presentation will discuss the air system in greater detail.

Click Click NextNext to continue. to continue.


Bleed Air System

Air for the bleed air system may be supplied from four different sources:

engine No. 1, engine No. 2, APU, or ground pneumatic air. Prior to engine

start, either the APU or ground pneumatic air may be utilized as the bleed source

(the ground pneumatic air is usually only utilized when the APU is not available). After engine start, the engines are the

normal bleed source.

APUbleedvalve

APU

No. 1 engine



valve


No. 2 engine




valve



Bleed Air System

Engine bleed air is obtained from either the 5th or 9th stage of the high pressure compressor section. The 5th stage is

normally utilized for bleed air. During low engine rpm, the 5th stage may not be sufficient to meet system demands.

Therefore the 9th stage modulating and shutoff valve opens and 5th stage air is no

longer utilized.

APUbleedvalve

APU

No. 1 engine



valve


No. 2 engine




valve



Bleed Air System

During normal operations, the isolation valve isolates the left and right side of the pneumatic

manifold. With the isolation valve switch in AUTO, both BLEED switches ON, and both PACK

switches in AUTO or HIGH, the isolation valve is closed. The isolation valve will automatically open if either PACK or either BLEED switch is

positioned to OFF. The APU bleed air switch does not affect isolation valve position. The isolation

valve is AC powered.

APUbleedvalve

APU

No. 1 engine



valve


No. 2 engine




valve


Isolation valve


Bleed Air System

Each engine has its own bleed valve. The valve acts as a pressure regulator and shutoff valve (PRSOV). With electrical

power (DC) and the BLEED switch ON, the valve remains open as long as there is

enough engine bleed air pressure to keep it open (electrically activated,

pneumatically operated).

APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



Bleed Air System

If engine bleed air temperature or pressure exceeds a predetermined limit, the BLEED TRIP OFF light illuminates and the respective bleed

valve automatically closes. In this scenario, the TRIP RESET button must be pushed in order to regain control of the bleed valve and extinguish

the BLEED TRIP OFF light.APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve


P T T P


Bleed Air System

When open, the APU bleed valve allows bleed air to flow to the left side of the pneumatic manifold.

APU bleed air can access the right side of the pneumatic manifold if the isolation valve is open. Like the engine bleed vales, the APU bleed valve

is electrically (DC) activated, pneumatically operated.

APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve

P T T P



Bleed Air System

A wing-body overheat condition is caused by a bleed air leak somewhere in the left or right pneumatic manifold. The left pneumatic manifold has five overheat sensors and the right pneumatic manifold has three overheat sensors. Anytime a leak is

detected, the respective WING-BODY OVERHEAT light illuminates. The OVHT TEST button may be used to test the WING-BODY OVERHEAT lights.

Left engine strut sensor

Left inboard wing leading edge sensor

Left-hand airconditioning bay sensor

Keel beam sensor

Bleed duct from APU sensor

Right inboard wing leadingedge sensor

Right engine strut sensor

Right-hand air conditioningbay sensor


APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve


Air Conditioning System

Conditioned air for the cabin originates from the left and/or right PACK. Normally the left PACK utilizes bleed air from the No. 1 engine and the right PACK utilizes bleed air from the No. 2 engine. If necessary, APU bleed air may

be utilized to operate the left and/or right PACK. Ground pneumatic air may be utilized if

the APU is not available. A single PACK is capable of maintaining pressurization and acceptable temperatures throughout the

aircraft up to the maximum certified ceiling.

Left PACK Right PACK

RightPACKvalve

LeftPACKvalve



The ram air system provides ambient air to cool the bleed air. The cooling is

accomplished via two heat exchangers. Operation of the system is automatically

controlled by the PACK’s through operation of the ram air inlet door. The

ram air inlet door is in the full-open position when the aircraft is on the

ground, inflight with trailing edge flaps extended, or anytime the PACK

determines that is is necessary to maximize cooling of the bleed air.

Deflector door

Ram air inlet

Ram air inlet door


Deflector door

Ram air inlet

Ram air inlet door


APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

See picture of See picture of left ram air inlet doorleft ram air inlet door

See picture of See picture of right ram air inlet doorright ram air inlet door



A deflector door is installed near each ram air inlet to prevent slush or foreign

material from entering the ram air system while the aircraft is taxiing. The

deflector door is deployed when the aircraft is on the ground and is retracted

(faired) when the aircraft is in flight.

Deflector door

Ram air inlet

Ram air inlet door


Deflector door

Ram air inlet

Ram air inlet door


APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

See picture of See picture of left deflector doorleft deflector door

See picture of See picture of right deflector doorright deflector door


Turbofan valve

Turbofan valve

Deflector door

Ram air inlet

Ram air inlet door


Deflector door

Ram air inlet

Ram air inlet door



A turbofan is installed in each ram air system to augment the airflow by drawing ram air into the system.

Whenever a PACK is selected “ON,” an electrical signal (DC) is sent to the

turbofan valve to open. The valve will open if the aircraft is on the ground, or

inflight with trailing edge flaps extended. The turbofan operates utilizing bleed

air.

APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

Turbofan Turbofan


Turbofan valve

Turbofan valve


As bleed air enters a PACK, it is processed by an air cycle machine

(ACM) and two heat exchangers. The now processed air exits the PACK and flows to the air mix manifold where it combines with processed air from the other PACK. The air continues to the

cabin via the left and right sidewall risers. Some of the conditioned air from the left PACK is routed to the flight deck.

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Air Mix Manifold




APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves

Cold Hot

Waterseparator

Air mixvalves

Click here to see how bleedClick here to see how bleedair flows through a PACKair flows through a PACK


Turbofan valve

Turbofan valve


There are two air mix valves (hot and cold) associated with each PACK. They

are butterfly type valves that are connected via a common shaft. The

bleed air that flows through the cold air mix valve is processed by the PACK for cooling of the aircraft. The bleed air that flows through the hot air mix valve is not processed by the PACK. This air instead

bypasses the cooling cycle and eventually joins with the air that has

been processed by the PACK.

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Air Mix Manifold




APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves

Cold Hot

Waterseparator

Air mixvalves


Turbofan valve

Turbofan valve


With the temperature selectors in the AUTO mode, the air mix valves are

operated by an automatic temperature controller. With the temperature

selectors in the MANUAL mode, the automatic temperature controller is bypassed and the air mix valves are operated manually. Anytime a PACK valve closes, the respective air mix valves are driven to the “full-cold”

position. This aids in start up of the cooling cycle produced by the ACM.

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Air Mix Manifold




APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves

Cold Hot

Waterseparator

Air mixvalves


Turbofan valve

Turbofan valve


The ACM is composed of a compressor and a turbine that are connected via a

common shaft. The temperature of the bleed air is measured as air is discharged from the compressor, and also prior to air

entering the turbine. If either sensor detects bleed air temperature exceeding a

predetermined limit, the PACK valve closes, the air mix valves drive “full-cold,” and the PACK TRIP OFF light illuminates.

The TRIP RESET button must be pushed to extinguish the light and reset the system.

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Air Mix Manifold




APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves

Cold Hot

Waterseparator

Air mixvalves

T T T T


Turbofan valve

Turbofan valve

Air Conditioning SystemDeflector door

Ram air inlet

Ram air inlet door


Turbofan

Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Air Mix Manifold




APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves

Cold Hot

Waterseparator

Air mixvalves

T T T T

T

T

A bleed air temperature sensor is located in the riser leading to the flight deck and also in the right sidewall riser leading to the cabin. These sensors determine if there is an overheat condition in the

ducts. If either sensor detects bleed air temperature exceeding a predetermined limit, the air mix valves drive “full-cold,”

and the DUCT OVERHEAT light illuminates. The TRIP RESET button must

be pushed to extinguish the light and reset the system.


Turbofan valve

Turbofan valve


As stated in the previous slide, a DUCT OVERHEAT results in the air mix valves driving to the “full-cold” position. This

forces the PACK to produce cold air only. If this does not result in a lower air

temperature in the duct and air temperature instead continues to

increase, an additional temperature sensor signals the PACK valve to close. When the PACK valve closes, the air mix

valves drive “full-cold” and the PACK TRIP OFF light illuminates.

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Air Mix Manifold




APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves

Cold Hot

Waterseparator

Air mixvalves

T T T T

T

T

T

T


Turbofan valve

Turbofan valve


A ground air conditioning hose may be connected to the underside of the

aircraft fuselage. This preconditioned air flows directly into the air mix

manifold, up the sidewall risers and into the cabin. This air is not processed by

either PACK.

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Air Mix Manifold




APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves

Cold Hot

Waterseparator

Air mixvalves

T T T T

T

T

T

T



Turbofan valve

Turbofan valve


With both PACK's operating and both PACK switches positioned to AUTO, the PACK's provide “low flow” air. During single PACK operation, the operating

PACK automatically provides “high flow” air in order to maintain the necessary

ventilation rate. The automatic switching from “low flow” to “high flow” is

inhibited when the aircraft is on the ground or inflight with trailing edge flaps extended. This ensures adequate engine

power for single engine operation.

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Air Mix Manifold




APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves

Cold Hot

Waterseparator

Air mixvalves

T T T T

T

T

T

T



Turbofan valve

Turbofan valve


If a PACK switch is positioned to HIGH, that PACK will provide “high flow” air.

Additionally, it is possible to achieve “APU high air flow” when utilizing the APU as the bleed source. This only occurs while on the ground with the operating PACK switch positioned to

HIGH. This mode is designed to provide maximum airflow when the APU is the

only source of bleed air.

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Air Mix Manifold




APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves

Cold Hot

Waterseparator

Air mixvalves

T T T T

T

T

T

T



Turbofan valve

Turbofan valve


An AC powered recirculation fan is installed to help reduce the PACK load and engine bleed air demand. This is

accomplished by the fan drawing cabin air and electronics & equipment (E&E) air into a collector shroud located above the

forward cargo compartment. The fan then recirculates the air by routing it into

the mix manifold where it is directed back into the cabin.

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Air Mix Manifold




APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves

Cold Hot

Waterseparator

Air mixvalves

T T T T

T

T

T

T



Recircfan


Turbofan valve

Turbofan valve


The recirculation fan is signaled to operate when the RECIRC FAN switch is

positioned to AUTO. The recirculation fan will not operate if both PACK’s are operating and either PACK switch is

positioned to HIGH.

Deflector door

Ram air inlet

Ram air inlet door


Turbofan

Deflector door

Ram air inlet

Ram air inlet door

Turbofan


Air Mix Manifold




APUbleedvalve

APU

Bleedvalve

Bleedvalve

No. 1 engine



valve


Isolation valve

No. 2 engine




valve



RightPACKvalve

LeftPACKvalve

ColdHot

Waterseparator

Air mixvalves

Cold Hot

Waterseparator

Air mixvalves

T T T T

T

T

T

T



Recircfan


Pressurization SystemPressurization SystemCabin pressurization is controlled during all ground and flight phases by the Cabin Pressure Control Cabin pressurization is controlled during all ground and flight phases by the Cabin Pressure Control System (CPCS). The CPCS components includes the cabin pressurization panel, one pressure controller System (CPCS). The CPCS components includes the cabin pressurization panel, one pressure controller for both AUTO and STANDBY mode operation (located in E&E bay), cabin altitude panel, forward outflow for both AUTO and STANDBY mode operation (located in E&E bay), cabin altitude panel, forward outflow valve, main outflow valve, and multiple pressurization relief valves. Cabin pressure is maintained by valve, main outflow valve, and multiple pressurization relief valves. Cabin pressure is maintained by positioning the main outflow valve to regulate the airflow from the air conditioning system.positioning the main outflow valve to regulate the airflow from the air conditioning system.


Pressurization SystemPressurization SystemFour separate pressurization modes may be selected: AUTO, STANDBY, MANUAL AC, and MANUAL DC. Four separate pressurization modes may be selected: AUTO, STANDBY, MANUAL AC, and MANUAL DC. The AUTO mode is the normal mode of operation. It utilizes the pressure controller and the AUTO The AUTO mode is the normal mode of operation. It utilizes the pressure controller and the AUTO portion of the cabin pressurization panel. The STANDBY mode is the backup to the AUTO mode and is portion of the cabin pressurization panel. The STANDBY mode is the backup to the AUTO mode and is semiautomatic. It utilizes the pressure controller and the STANDBY portion of the cabin pressurization semiautomatic. It utilizes the pressure controller and the STANDBY portion of the cabin pressurization panel. If the AUTO mode and STANDBY mode are not available, the MANUAL mode is available and is panel. If the AUTO mode and STANDBY mode are not available, the MANUAL mode is available and is entirely pilot-controlled. The pilot has a choice between MAN AC control, or MAN DC control.entirely pilot-controlled. The pilot has a choice between MAN AC control, or MAN DC control.


Pressurization SystemPressurization SystemIn the AUTO mode of operation, aircraft altitude is sensed directly from the static ports, and barometric In the AUTO mode of operation, aircraft altitude is sensed directly from the static ports, and barometric corrections come from the Captain’s altimeter. In the STANDBY mode of operation, aircraft altitude is corrections come from the Captain’s altimeter. In the STANDBY mode of operation, aircraft altitude is sensed electrically from an air data computer, and barometric corrections come from the First Officer’s sensed electrically from an air data computer, and barometric corrections come from the First Officer’s altimeter. Barometric corrections are necessary to ensure that cabin pressure and landing field pressure altimeter. Barometric corrections are necessary to ensure that cabin pressure and landing field pressure are approximately the same at the time of landing.are approximately the same at the time of landing.


Pressurization SystemPressurization SystemCabin air outflow is controlled by the main outflow valve, forward outflow valve, and the automatic flow Cabin air outflow is controlled by the main outflow valve, forward outflow valve, and the automatic flow control valve. During flight with differential pressure greater than 2.5 psi, the automatic flow control control valve. During flight with differential pressure greater than 2.5 psi, the automatic flow control valve is closed and therefore the majority of air is exhausted out the main and forward outflow valves. A valve is closed and therefore the majority of air is exhausted out the main and forward outflow valves. A small amount of air is also exhausted through toilet and galley vents, miscellaneous fixed vents, and by small amount of air is also exhausted through toilet and galley vents, miscellaneous fixed vents, and by seal leakage.seal leakage.

The main outflow valve can be actuated by either an AC or DC motor. The AC motor is utilized when the The main outflow valve can be actuated by either an AC or DC motor. The AC motor is utilized when the pressurization system is in the AUTO or MAN AC modes. The DC motor is utilized when the pressurization system is in the AUTO or MAN AC modes. The DC motor is utilized when the pressurization system is in the STANDBY or MAN DC modes. AC motor speed is faster than DC motor pressurization system is in the STANDBY or MAN DC modes. AC motor speed is faster than DC motor speed. A majority of the air that is circulated throughout the cabin is drawn out the foot-level grills, then speed. A majority of the air that is circulated throughout the cabin is drawn out the foot-level grills, then around the aft cargo compartment for heating, and exhausted overboard out the main outflow valve.around the aft cargo compartment for heating, and exhausted overboard out the main outflow valve.

The forward outflow valve assists in maintaining cabin pressure. However, the main purpose of the The forward outflow valve assists in maintaining cabin pressure. However, the main purpose of the forward outflow valve is to discharge warm air that has circulated around the forward cargo compartment forward outflow valve is to discharge warm air that has circulated around the forward cargo compartment for heating. The valve is open when the main outflow valve is open more than 4.5 degrees, and is closed for heating. The valve is open when the main outflow valve is open more than 4.5 degrees, and is closed when the main outflow valve is within 0.5 degrees being closed. In addition, the forward outflow valve is when the main outflow valve is within 0.5 degrees being closed. In addition, the forward outflow valve is closed anytime the recirculation fan is operating, regardless of the main outflow valve position. The closed anytime the recirculation fan is operating, regardless of the main outflow valve position. The forward outflow valve does not modulate; it is either fully open or fully closed.forward outflow valve does not modulate; it is either fully open or fully closed.

Two positive pressure relief valves are installed to prevent cabin-to-ambient differential pressure from Two positive pressure relief valves are installed to prevent cabin-to-ambient differential pressure from exceeding 8.65 psi. The valves operate independently of each other and any other aircraft system.exceeding 8.65 psi. The valves operate independently of each other and any other aircraft system.

The negative pressure relief valve is installed to prevent a negative cabin-to-ambient differential pressure The negative pressure relief valve is installed to prevent a negative cabin-to-ambient differential pressure which may result in damage to the aircraft. The valve opens when differential pressure equals –1.0.which may result in damage to the aircraft. The valve opens when differential pressure equals –1.0.

See picture ofSee picture ofmain outflow valve main outflow valve

See picture ofSee picture offorward outflow valve forward outflow valve

See picture of positive See picture of positive pressure relief valves pressure relief valves

See picture of negative See picture of negative pressure relief valvepressure relief valve


Pressurization SystemPressurization SystemAUTO Mode OperationAUTO Mode Operation

When operating in the AUTO mode (pressurization mode selector in AUTO), two values must be set on When operating in the AUTO mode (pressurization mode selector in AUTO), two values must be set on the cabin pressurization panel prior to takeoff: FLT ALT (cruse altitude) and LAND ALT (destination the cabin pressurization panel prior to takeoff: FLT ALT (cruse altitude) and LAND ALT (destination airport elevation). While on the ground, ambient pressure is an automatic input into the pressure airport elevation). While on the ground, ambient pressure is an automatic input into the pressure controller.controller.

Prior to takeoff with the FLT/GRD switch positioned to GRD, the main outflow valve drives to the full-open Prior to takeoff with the FLT/GRD switch positioned to GRD, the main outflow valve drives to the full-open position and the cabin remains unpressurized. When the FLT/GRD switch is positioned to FLT, the position and the cabin remains unpressurized. When the FLT/GRD switch is positioned to FLT, the controller signals the main outflow valve to modulate toward closed, slightly pressurizing the cabin to controller signals the main outflow valve to modulate toward closed, slightly pressurizing the cabin to approximately 200 feet below takeoff elevation. This pressurization while still on the ground ensures that approximately 200 feet below takeoff elevation. This pressurization while still on the ground ensures that the transition to pressurized flight is more gradual. It also allows the pressurization system to better the transition to pressurized flight is more gradual. It also allows the pressurization system to better respond to ground effect pressure changes during takeoff.respond to ground effect pressure changes during takeoff.



Once airborne, the pressure controller maintains a proportional differential pressure between cabin and Once airborne, the pressure controller maintains a proportional differential pressure between cabin and aircraft altitude. By increasing cabin altitude at a rate which is proportional to the aircraft climb rate, the aircraft altitude. By increasing cabin altitude at a rate which is proportional to the aircraft climb rate, the change in cabin altitude is held to the minimum rate required.change in cabin altitude is held to the minimum rate required.



The OFF SCHED DESCENT light illuminates if the aircraft begins to descend prior to reaching within The OFF SCHED DESCENT light illuminates if the aircraft begins to descend prior to reaching within 0.25 psi of the altitude set in the FLT ALT indicator. Because the altitude in the FLT ALT indicator was 0.25 psi of the altitude set in the FLT ALT indicator. Because the altitude in the FLT ALT indicator was never achieved, the pressure controller retains information regarding takeoff field elevation and will never achieved, the pressure controller retains information regarding takeoff field elevation and will therefore program the cabin to normally depressurize back to the airport of origin without any further therefore program the cabin to normally depressurize back to the airport of origin without any further pilot inputs. This feature is especially beneficial if the aircraft is returning to the airport of origin.pilot inputs. This feature is especially beneficial if the aircraft is returning to the airport of origin.



If the aircraft is If the aircraft is returning to the airport of originreturning to the airport of origin during an OFF SCHED DESCENT, it is recommended not during an OFF SCHED DESCENT, it is recommended not to change the altitude set in the FLT ALT indicator (e.g. setting current aircraft altitude). If the FLT ALT to change the altitude set in the FLT ALT indicator (e.g. setting current aircraft altitude). If the FLT ALT indicator is set to current aircraft altitude, the automatic abort capability to the takeoff field elevation will indicator is set to current aircraft altitude, the automatic abort capability to the takeoff field elevation will be lost. Landing field elevation of the origin airport would then have to be set in the FLT ALT indicator in be lost. Landing field elevation of the origin airport would then have to be set in the FLT ALT indicator in order to properly depressurize. Setting current altitude in the FLT ALT indicator does, however, order to properly depressurize. Setting current altitude in the FLT ALT indicator does, however, extinguish the OFF SCHED DESCENT light. extinguish the OFF SCHED DESCENT light.

If the aircraft is If the aircraft is notnot returning to the airport of origin during a OFF SCHED DESCENT, the LAND ALT returning to the airport of origin during a OFF SCHED DESCENT, the LAND ALT indicator must be set to the new landing field elevation.indicator must be set to the new landing field elevation.

Note: The automatic abort capability to the takeoff field elevation will also be lost if the FLT ALT selector Note: The automatic abort capability to the takeoff field elevation will also be lost if the FLT ALT selector is depressed during the climb.is depressed during the climb.



The cruise mode is activated when the aircraft climbs to within 0.25 psi of the altitude set in the FLT ALT The cruise mode is activated when the aircraft climbs to within 0.25 psi of the altitude set in the FLT ALT indicator. During cruise above 28,000 feet, the pressure controller maintains a maximum differential indicator. During cruise above 28,000 feet, the pressure controller maintains a maximum differential pressure of 7.8 psi. During cruise below 28,000 feet, the pressure controller maintains a maximum pressure of 7.8 psi. During cruise below 28,000 feet, the pressure controller maintains a maximum differential pressure of 7.45 psi. Deviations from flight altitude may cause the differential pressure to differential pressure of 7.45 psi. Deviations from flight altitude may cause the differential pressure to vary as the pressure controller modulates the main outflow valve to maintain a constant cabin altitude.vary as the pressure controller modulates the main outflow valve to maintain a constant cabin altitude.



The descent mode is activated when the aircraft descends to 0.25 psi below the altitude set in the FLT The descent mode is activated when the aircraft descends to 0.25 psi below the altitude set in the FLT ALT indicator. During descent, the pressure controller maintains a proportional differential pressure ALT indicator. During descent, the pressure controller maintains a proportional differential pressure between cabin and aircraft altitude. The cabin will depressurize to an altitude which is slightly lower than between cabin and aircraft altitude. The cabin will depressurize to an altitude which is slightly lower than the altitude which is set in the LAND ALT indicator (landing field elevation). This slightly pressurized the altitude which is set in the LAND ALT indicator (landing field elevation). This slightly pressurized landing ensures that rapid changes in altitude during approach will result in minimum cabin pressure landing ensures that rapid changes in altitude during approach will result in minimum cabin pressure changes.changes.



Once on the ground, positioning the FLT/GRD switch to GRD drives the main outflow valve full-open and Once on the ground, positioning the FLT/GRD switch to GRD drives the main outflow valve full-open and depressurizes the aircraft. Having the main outflow valve full open also prevents the equipment cooling depressurizes the aircraft. Having the main outflow valve full open also prevents the equipment cooling fan from depressurizing the aircraft to a negative pressure.fan from depressurizing the aircraft to a negative pressure.



The AUTO FAIL light will illuminate for any one of the following three conditions:The AUTO FAIL light will illuminate for any one of the following three conditions:• Loss of AC power for more than 15 secondsLoss of AC power for more than 15 seconds• Excessive rate of cabin pressure change (+/- 1800 feet/min.)Excessive rate of cabin pressure change (+/- 1800 feet/min.)• Cabin altitude in excess of 13,875 feetCabin altitude in excess of 13,875 feet

When the AUTO FAIL light illuminates, the pressure controller automatically switches to the STANDBY When the AUTO FAIL light illuminates, the pressure controller automatically switches to the STANDBY mode and the STANDBY light illuminates. Positioning the pressurization mode selector to STBY will mode and the STANDBY light illuminates. Positioning the pressurization mode selector to STBY will extinguish the AUTO FAIL light.extinguish the AUTO FAIL light.


Pressurization SystemPressurization SystemSTANDBY Mode OperationSTANDBY Mode Operation

To operate in the STANDBY mode, simply position the pressurization mode selector to STBY. This action To operate in the STANDBY mode, simply position the pressurization mode selector to STBY. This action signals the pressure controller to operate in the STANDBY mode and also illuminates the STANDBY light. signals the pressure controller to operate in the STANDBY mode and also illuminates the STANDBY light.

Prior to takeoff with the FLT/GRD switch positioned to GRD, the main outflow valve drives to the full-open Prior to takeoff with the FLT/GRD switch positioned to GRD, the main outflow valve drives to the full-open position and the cabin remains unpressurized. When the FLT/GRD switch is positioned to FLT, the position and the cabin remains unpressurized. When the FLT/GRD switch is positioned to FLT, the controller signals the main outflow valve to modulate toward closed in an attempt to pressurize the cabin controller signals the main outflow valve to modulate toward closed in an attempt to pressurize the cabin to the altitude set in the CAB ALT indicator. The CAB ALT indicator should be set to 200 feet below to the altitude set in the CAB ALT indicator. The CAB ALT indicator should be set to 200 feet below takeoff field elevation. This pressurization while still on the ground ensures that the transition to takeoff field elevation. This pressurization while still on the ground ensures that the transition to pressurized flight is more gradual. It also allows the pressurization system to better respond to ground pressurized flight is more gradual. It also allows the pressurization system to better respond to ground effect pressure changes during takeoff.effect pressure changes during takeoff.

For this “demonstration flight” in For this “demonstration flight” in the STANDBY mode, the following the STANDBY mode, the following elevations/altitudes are assumed:elevations/altitudes are assumed:

Takeoff field elevation:Takeoff field elevation: 1,700 feet1,700 feetCruise altitude:Cruise altitude: 30,000 feet30,000 feetLading field elevation:Lading field elevation: 1,300 feet1,300 feet



Once airborne, the pilot should reference the cabin/flight altitude placard. The CAB ALT indicator should Once airborne, the pilot should reference the cabin/flight altitude placard. The CAB ALT indicator should then be set to the isobaric cabin altitude, based on the proposed cruise altitude and differential pressure. then be set to the isobaric cabin altitude, based on the proposed cruise altitude and differential pressure. For example, if the proposed cruise altitude is 30,000 feet, then the CAB ALT indicator should be set to For example, if the proposed cruise altitude is 30,000 feet, then the CAB ALT indicator should be set to 5,100 feet. 5,100 feet.

The cabin rate selector should also be set to the desired cabin rate of pressure change. Recall that DECR The cabin rate selector should also be set to the desired cabin rate of pressure change. Recall that DECR has a rate of change equal to 50 feet/min., the index has a rate of change equal to 300 feet/min., and INCR has a rate of change equal to 50 feet/min., the index has a rate of change equal to 300 feet/min., and INCR has a rate of change equal to 2000 feet/min.has a rate of change equal to 2000 feet/min.





When descent begins, the CAB ALT indicator should be set to 200 feet below landing field elevation. This When descent begins, the CAB ALT indicator should be set to 200 feet below landing field elevation. This slightly pressurized landing ensures that rapid changes in altitude during approach will result in slightly pressurized landing ensures that rapid changes in altitude during approach will result in minimum cabin pressure changes.minimum cabin pressure changes.





Once on the ground, positioning the FLT/GRD switch to GRD drives the main outflow valve full-open and Once on the ground, positioning the FLT/GRD switch to GRD drives the main outflow valve full-open and depressurizes the aircraft. Having the main outflow valve full open also prevents the equipment cooling depressurizes the aircraft. Having the main outflow valve full open also prevents the equipment cooling fan from depressurizing the aircraft to a negative pressure.fan from depressurizing the aircraft to a negative pressure.


Pressurization SystemPressurization SystemMANUAL Mode OperationMANUAL Mode Operation

To operate in the MANUAL mode, simply position the pressurization mode selector to either MAN AC or To operate in the MANUAL mode, simply position the pressurization mode selector to either MAN AC or MAN DC. This action signals the pressure controller to operate in the MANUAL mode and also MAN DC. This action signals the pressure controller to operate in the MANUAL mode and also illuminates the MANUAL light. illuminates the MANUAL light.

Operation in the MANUAL mode assumes that both the AUTO and STANDBY modes have failed. By Operation in the MANUAL mode assumes that both the AUTO and STANDBY modes have failed. By using the main outflow valve switch, the pilot modulates the position of the main outflow valve to using the main outflow valve switch, the pilot modulates the position of the main outflow valve to maintain the desired cabin pressure. MAN AC utilizes the AC motor, while MAN DC utilizes the DC motor. maintain the desired cabin pressure. MAN AC utilizes the AC motor, while MAN DC utilizes the DC motor. AC motor speed is faster than DC motor speed. Position of the main outflow valve may be observed in AC motor speed is faster than DC motor speed. Position of the main outflow valve may be observed in the main outflow valve position indicator. the main outflow valve position indicator.


Cabin Pressure Control System Schematic

Conditioned air from overheadand sidewall outlets

Static ports

Negative pressure

relief valve

Main outflow valve

Positive pressure relief valve

Positive pressure relief valve

Air/Groundsafety sensor

Forward outflow valve

Auto transfer to STANDBY mode

ADC

Cabinsenseport

DC AC

Altimeter barometric settings

CA FO

Static ports


Equipment Cooling

The equipment cooling system cools electronic equipment in the flight deck and E&E bay. The cooling system consists of an exhaust duct and two fans

(normal and alternate). The exhaust duct collects warm air from the instrument panels, circuit breaker panels, and E&E bay racks.

Main instrument panel cooling duct

Normal exhaust fan

Alternate exhaust fan

To shroud underneath forward cargo compartment

Automatic flow control valve

Circuit breaker panel cooling duct

E&E bay cooling ducts

E&E exhaust port


Main instrument panel cooling duct

Normal exhaust fan

Alternate exhaust fan

To shroud underneath forward cargo compartment

Automatic flow control valve

Circuit breaker panel cooling duct

E&E bay cooling ducts

E&E exhaust port

Equipment Cooling

If differential pressure is less than 2.5 psi, the automatic flow control valve is open and the warm exhaust air is discharged overboard via the E&E exhaust port. The E&E exhaust port is located on the underside of the fuselage, aft of the nose gear. If differential pressure is greater than 2.5 psi, the automatic flow control valve closes and the warm air is redirected to a shroud underneath the

forward cargo compartment. The air now flows to the lining of the compartment, where radiant heat is utilized for forward compartment heating. None of the warm air enters the compartment

during this process. The air now collects in a shroud above the compartment. From the shroud, the air is either exhausted overboard through the forward outflow valve or, if the recirculation fan

is operating, the air is drawn into the recirculation fan and directed back into the cabin.

See picture ofSee picture ofE&E exhaust port E&E exhaust port

Warm air being drawn into the

cooling ducts by the exhaust fan

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B737-300/400 Air systems

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Transcript of B737-300/400 Air systems