B757  

 Air Systems 

DO NOT USE FOR FLIGHT 

2.20 Air Systems-Air Conditioning System DescriptionAir Conditioning IntroductionThe air conditioning system supplies conditioned bleed air and recirculated cabin air at a controlled temperature throughout the airplane. The system supplies conditioned air to the flight deck shoulder heaters.The system supplies ventilation for the cabin:

• lavatories• galleys• individual passenger seat gaspers.

Pack control, zone temperature control, cabin air recirculation, fault detection, and overheat protection are all automatic.The airplane is divided into three temperature zones: the flight deck and two cabin zones.

Air Conditioning PacksTwo identical air conditioning packs cool bleed air from the engines, APU, or high pressure air from a ground source. Bleed air is precooled before entering the pack. The packs are controlled by two identical pack controllers. Pack output is automatically increased during high pack demand periods (to compensate for a failed pack or recirculation fan), or limited during high bleed air demand periods (such as with an engine inoperative).

Air Conditioning Automatic ModeWith the pack selector in the AUTO position, pack output temperature is determined by the cabin temperature controller. Zone temperature is then satisfied by the zone temperature controllers using trim air.

Air Conditioning Standby ModeWith the pack selector in the standby mode, pack output temperature is determined by the position of the pack selector:

• N (normal) – constant, moderate temperature• C (cool) – full cold• W (warm) – full warm.

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Ground Conditioned Air OperationWhen a ground source of conditioned air is available, it may be used to supply conditioned air directly to the cabin distribution system, eliminating the need for pack operation.

Pack Non–Normal OperationPack control, fault detection, and overheat protection are all automatic.The pack INOP light illuminates and the EICAS advisory message L or R PACK TEMP displays for all pack control system faults and overheats.When an automatic control system fault or a pack outlet overheat is detected, the pack continues to operate in an uncontrolled, degraded condition, requiring crew interaction.The pack valve closes and the pack is shut down automatically when an internal pack overheat is detected. The PACK OFF light illuminates and the EICAS advisory message L or R PACK OFF displays in addition to the PACK TEMP indications.If the INOP light remains illuminated after selecting STBY, the fault is a pack overheat. After the pack has cooled, an attempt to restore pack operation may be made by pushing the PACK RESET switch.

Air DistributionConditioned air from the packs flows into a mix manifold where it mixes with air from two recirculation fans. Recirculation fans maintain overall cabin air circulation while allowing a reduction of cabin air ventilation, permitting the packs to be operated at a reduced flow. The mixed air is then ducted into the cabin.The flight deck receives 100% fresh conditioned air from the left pack only and is maintained at a slightly higher pressure than the passenger cabin. This prevents smoke from entering the flight deck. When the left pack is inoperative, the flight deck receives air from the mix manifold.The left recirculation fan draws air through the forward E/E system and returns it to the mix manifold. Air that moves from the cabin to the lower deck either exhausts overboard through the outflow valve or is drawn into the right recirculation fan and returns to the mix manifold.The right recirculation fan can be turned off for several minutes to provide a more rapid exchange of air. The left recirculation fan should not be turned off as this causes the overboard exhaust valve to latch open. Maintenance action is required to reset the OVBD EX VAL OPEN status message.

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The recirculation fan INOP light illuminates and the EICAS advisory message L or R RECIR FAN displays whenever a recirculation fan fails or the switch is off. A slight increase in fuel consumption occurs for each fan that is off.

Temperature ControlThe airplane is divided into three temperature control compartments:

• flight deck• forward cabin• aft cabin.

The pack controllers regulate the pack output air temperature to satisfy the temperature requirement of the compartment requiring the coolest air. Hot trim air from the bleed air system is added through trim air valves to control the temperature in each of the other compartments. Each temperature control compartment has an associated temperature control.A compartment INOP light illuminates and the EICAS advisory message FLT DECK TEMP, FWD CABIN TEMP, or AFT CABIN TEMP displays to indicate:

• zone temperature controller failure• zone selector is in the OFF position• trim air switch is OFF

Temperature Control With Loss of Trim Air SystemDuring operation with the trim air system off, the packs attempt to maintain all compartments at an average temperature. The trim air OFF light illuminates and the EICAS advisory message TRIM AIR displays when a TRIM AIR switch is off.

Shoulder and Foot HeatersFlight crew shoulder heat is provided by electric heaters in the ducts that supply conditioned air to the side windows. Foot heat is provided by electric heating elements only, with no airflow. The high setting for both shoulder and foot heat is available in flight only.

Forward Equipment Cooling SystemForward equipment cooling supplies cooling air to the equipment in the forward equipment racks and the flight deck avionics. The system has a supply fan that draws cooling air from the cabin and forces it through the equipment racks and avionics. The air is then exhausted into the air conditioning mix manifold by the left recirculation fan. If the differential pressure is low, the overboard exhaust valve automatically opens and most of the air is exhausted overboard.

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An auxiliary fan automatically operates to provide cooling for essential avionics and electrical equipment if the alternate supply fan has been selected but both supply fans are inoperative. However, non–essential avionics and electrical equipment are subject to imminent failure. The auxiliary fan can be powered by the hydraulic driven generator.On the ground, the OVHT light illuminates, the EQPT OVHT message displays and the ground crew call horn sounds if insufficient cooling airflow is detected.

Equipment SmokeThe equipment cooling SMOKE light illuminates and the EICAS advisory message FWD EQPT SMOKE displays when smoke is detected in the equipment cooling system.The following items, which may be observed in the flight deck, occur automatically to help evacuate the smoke:

• one or both recirculation fans turn off• one or both air conditioning packs switch to high flow• the overboard exhaust valve is latched open.

When smoke is no longer detected, the recirculation fans and air conditioning packs automatically return to normal operation.

Cargo Heat SystemCargo compartment heating and ventilation is completely automatic. There are no controls or indicators in the cockpit.

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Air Conditioning System Schematic

OFFOFFC C

AFT CABAUTO

FWD CABAUTO

PACKOFF

INOP

INOP

COMPT TEMP

INOP INOP

RESET

R PACKL PACK

TRIM AIR L R

RESET

RECIRCFAN

MIX MANIFOLD

PNEUMATICSUPPLY

PNEUMATICSUPPLY

AUTOOFF N

C

W

STBY

AUTOOFF N

C

W

STBY

AIR

PACK AIR

EXHAUST AIR

MIX MANIFOLD

TRIM AIR

PACKOFF

INOP

OFFC

FLT DKAUTO

ON

INOP

ON

INOP

ON

OFF

WWW

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2.30 Air Systems-Pressurization System DescriptionPressurization IntroductionCabin pressurization is controlled by adjusting the discharge of conditioned cabin air through the outflow valve. Positive pressure relief valves and negative pressure relief doors protect the fuselage against excessive pressure differential.The pressurization system has automatic and manual operating modes.

Pressurization System Automatic OperationThe pressurization system is in the automatic mode when the cabin altitude mode selector is set to AUTO 1 or AUTO 2. If the selected auto mode fails, control is automatically switched to the other auto mode.In the automatic mode, the pressurization system uses ambient pressure data from the air data system in conjunction with the selected cabin auto rate, the takeoff altitude and the indicated landing altitude to calculate the cabin pressurization schedule.

TakeoffFor takeoff, the system supplies a small positive pressurization to cause a smooth cabin altitude transition.

ClimbDuring climb, cabin altitude increases on a schedule related to the takeoff field elevation, airplane altitude, and the selected auto climb rate limit.If the maximum cabin pressure differential is reached, cabin climb rate becomes a function of airplane climb rate, while maintaining the maximum differential pressure.

CruiseShortly after the airplane levels off, the system enters the cruise mode. The landing altitude and the scheduled cabin altitude are compared and the higher of these two is selected for the cruise cabin altitude. If necessary, the cabin climbs to the cruise cabin altitude at one–half the auto rate or descends to the cruise cabin altitude at the auto rate.The cruise cabin altitude does not change for minor altitude variations. A significant altitude change causes the system to re–enter the climb mode or to enter the descent mode.

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Descent and LandingDuring descent, cabin altitude decreases to slightly below the selected landing altitude. This ensures that the airplane lands pressurized. Landing altitude barometric pressure correction comes from the captain’s altimeter.At touchdown, the outflow valve opens to depressurize the airplane.

Non–Normal IndicationsIf the cabin altitude climbs above 10,000 feet, the CABIN ALT and CABIN ALTITUDE lights illuminate and the EICAS warning message CABIN ALTITUDE displays. The lights extinguish and the EICAS message blanks when the cabin altitude descends below 8,500 feet.The AUTO INOP light illuminates and the EICAS caution message CABIN AUTO INOP displays when automatic pressurization control fails or when cabin altitude MODE SELECT is MAN. Manual operation is required if the automatic system fails.Only the automatic mode is equipped with an aneroid switch that automatically closes the outflow valve when the cabin altitude exceeds 11,000 feet. The manual mode has no auto closure feature.To operate the pressurization system manually:

• set the cabin altitude MODE SELECT to MAN• hold the cabin altitude MANUAL control to CLIMB to move the outflow

valve toward open and cause the cabin altitude to climb• hold the cabin altitude MANUAL control to DESCEND to move the

outflow valve toward closed and cause the cabin altitude to descend.

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2.40 Air Systems-Bleed Air System DescriptionBleed Air IntroductionBleed air can be supplied by the engines, APU, or a ground air source.Bleed air is used for:

Engine Bleed Air SupplyEngine bleed air comes from either the high pressure (HP) or the low pressure (LP) engine compressor sections. LP air is used during high power setting operations. HP air is used during descent and other low power setting operations.The engine bleed air valves are armed when the engine bleed air switches are selected ON. The valves are pressure actuated and remain closed until engine bleed air pressure is sufficient to cause forward flow. The valves may close when the APU is starting either engine. The valves may close when ground pneumatic air is connected or during periods of low engine bleed air demand, such as when the air conditioning packs are OFF. The engine bleed air OFF light illuminates and the EICAS advisory message L or R ENG BLEED OFF displays when the engine bleed air valve is closed.The HI STAGE light illuminates and the EICAS advisory message L or R ENG HI STAGE displays when engine bleed air pressure is excessive and the high pressure bleed air valve automatically locks closed.The engine BLEED light illuminates and the EICAS Caution message L or R ENG BLEED VAL displays if the engine bleed air temperature is excessive.

APU Bleed Air SupplyAPU bleed air is used primarily during ground operations for air conditioning pack operation and engine starting. In flight, APU bleed air is available up to approximately 17,000 feet.The check valve in the APU supply line prevents reverse flow of bleed air from the duct into the APU. The APU bleed air VALVE light illuminates and the EICAS advisory message APU BLEED VAL displays when the APU Bleed Valve position disagrees with the commanded position.

• air conditioning• pressurization• engine start

• wing and engine anti–ice• hydraulic reservoir

pressurization.

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Ground Pneumatic Air SupplyExternal connectors are provided to connect a ground source of high pressure air directly to the bleed air duct. Check valves prevent reverse flow of bleed air from the bleed air duct to the connectors.

Bleed Air Duct SystemThe duct pressure indicator displays the pressure in the left and right bleed air ducts.The isolation valve separates the bleed air ducts into isolated segments. The isolation valve is normally closed except for engine start or single bleed source operation.The isolation VALVE light illuminates and the EICAS advisory message BLEED ISLN VAL displays when the isolation valve position disagrees with the commanded position.The DUCT LEAK light illuminates and the EICAS caution message L or R BLD DUCT LEAK displays when a high temperature bleed air leak is detected.

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Bleed Air System Schematic

DUCTLEAK

BLEED

HI STAGE

DUCTLEAK

BLEED

HI STAGE

60 80

20 0

DUCTPRESSPSI

40

PANEL FLOW LINESFLOW LINES NOT ON PANEL

APU

LP

HPSTARTER

OFF

VALVE

OFF

VALVE

ISOLATION

R ENGL ENG APU

BLEED AIR

ANTI-ICE

GROUNDPNEUMATIC

GROUNDPNEUMATIC

L PACK R PACK

L WING ANTI-ICE HYDRAULIC RESERVOIRS

LP

HP

ENGINE

R WING ANTI-ICE HYDRAULIC RESERVOIRS

STARTER

ANTI-ICEENGINE

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DUCTLEAK

BLEED

HI STAGE

DUCTLEAK

BLEED

HI STAGE

60 80

20 0

DUCTPRESSPSI

40

PANEL FLOW LINESFLOW LINES NOT ON PANEL

APU

LP

HP

STARTER

OFF

VALVE

OFF

VALVE

ISOLATION

R ENGL ENG APU

BLEED AIR GROUNDPNEUMATICGROUND

PNEUMATIC

L PACK R PACK

L WING ANTI-ICE HYDRAULIC RESERVOIRS

LP

HP

R WING ANTI-ICE HYDRAULIC RESERVOIRS

STARTER

ENGINEANTI-ICE

ENGINEANTI-ICE

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2.50 Air Systems-EICAS MessagesAir Systems EICAS MessagesThe following EICAS messages can be displayed.

Message Level Light Aural Condition

APU BLEED VAL Advisory VALVE APU bleed valve position disagrees with the commanded position.

L BLD DUCT LEAK

R BLD DUCT LEAK

Caution DUCT LEAK

Beeper A high temperature bleed air leak is detected.

BLEED ISLN VAL Advisory VALVE Bleed isolation valve position disagrees with the commanded position.

CABIN ALTITUDE Warning CABIN ALTITUDE,CABIN ALT

Siren Cabin altitude excessive.

CABIN AUTO INOP Caution AUTO INOP

Beeper Automatic pressurization control has failed or the cabin altitude mode selector is in manual.

AFT CABIN TEMP

FWD CABIN TEMP

Advisory INOP A fault in the zone temperature controller or trim air switch OFF.

L ENG BLEED OFF

R ENG BLEED OFF

Advisory OFF Engine bleed air valve is closed for a system fault.

L ENG BLEED VAL

R ENG BLEED VAL

Caution BLEED Beeper Engine bleed air temperature excessive.

L ENG HI STAGE

R ENG HI STAGE

Advisory HI STAGE Engine bleed system pressure is excessive and the high pressure bleed air valve has automatically locked closed.

EQPT OVHT Advisory OVHT Forward equipment cooling system inoperative.

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Message Level Light Aural Condition

FWD EQPT SMOKE Advisory SMOKE Smoke detected in the forward equipment cooling ducts.

FLT DECK TEMP Advisory INOP Duct overheat, fault in the zone temperature controller, or trim air switch off.

L PACK OFF

R PACK OFF

Advisory PACK OFF Pack valve is closed.

L PACK TEMP

R PACK TEMP

Advisory INOP Automatic control system fault or overheat.

L RECIR FAN

R RECIR FAN

Advisory INOP Fan is failed or not operating.

TRIM AIR Advisory OFF Trim air switch off.

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2.10 Air Systems-Controls and IndicatorsAir Conditioning System

Air Conditioning Control Panel

OVERHEAD PANEL

YBTS

W

C

NAUTO

OFF

RESETR PACK

RESETL PACK

LTRIM AIR

WOFFCOFF WOFFCWC

AUTOAFT CAB

AUTOFWD CAB

AUTOFLT DK

OFFOFFPACKPACK

INOPINOP

ONON

INOP

INOP

ON

OFF INOP

COMPT TEMP

INOPINOP

RECIRC FANR

YBTS

W

C

NAUTO

OFF

9

10

11

1

2

3

4

5

6

78

1 Compartment Temperature (COMPT TEMP) IndicatorsDisplays actual temperature sensed in the compartment.

2 Compartment Temperature Inoperative (INOP) LightsIlluminated (amber) –

• fault in the zone temperature controller• the Compartment Temperature Control is OFF• the trim air switch is OFF.

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3 Compartment Temperature ControlsAUTO –

• provides automatic compartment temperature control• rotating the control toward C (cool) or W (warm) sets the desired

temperature between 18 degrees C and 30 degrees C.OFF –

• closes the compartment trim air valve• the compartment temperature INOP light illuminates.

4 TRIM AIR SwitchON – the trim air valve is commanded open.Off (ON not visible) – the trim air valve is commanded closed.

5 Trim Air OFF LightIlluminated (amber) – the TRIM AIR switch is off.

6 PACK RESET SwitchesPush – resets an overheated pack if the pack has cooled to a temperature below the overheat level.

7 Pack Inoperative (INOP) LightsIlluminated (amber) –

• the pack is overheated• fault in the automatic control system.

8 PACK OFF LightsIlluminated (amber) – the pack valve is closed.

9 PACK Control SelectorsOFF – closes the pack valve.AUTO – the pack is automatically controlled.STBY–

• N (normal) – regulates the pack outlet temperature to a constant, moderate temperature

• C (cool) – sets the pack to full cold operation• W (warm) – sets the pack to full warm operation.

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10 Recirculation Fan (RECIRC FAN) Switches• ON – the recirculation fan operates• Off (ON not visible) – the recirculation fan does not operate.

11 Recirculation Fan Inoperative (INOP) LightsIlluminated (amber) –

• the recirculation fan is failed or not operating• the RECIRC FAN switch is off.

Shoulder and Foot Heaters

1 FOOT HEATERS Switch• HIGH – the under–floor electric heater operates on high setting (in flight

only).• LOW – the under–floor electric heater operates on low setting.• OFF – the under–floor electric heater is not operating.

2 SHOULDER HEATERS Switch• HIGH – the electric heater adds heat at high setting to the conditioned air

flowing at shoulder level (in flight only).• LOW – the electric heater adds heat at low setting to the conditioned air

flowing at shoulder level.• OFF – the electric heater is not operating (no heat added to the

conditioned air flowing at shoulder level.).

LOW

HI

OFF

HI

OFF

HEATERS

SHOULDER

FOOT

LOW

LEFT AND RIGHT SIDEWALL

1

2

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Equipment Cooling Panel

1 Equipment Cooling SMOKE LightIlluminated (amber) – smoke is detected in the forward equipment cooling ducts.

2 Alternate (ALTN) Equipment Cooling SwitchALTN –

• activates the alternate supply fan• activates the auxiliary fan, if the alternate supply fan fails.

3 Equipment Cooling Overheat (OVHT) LightIlluminated (amber) –

• insufficient airflow (on the ground)• the supply fan is inoperative• the alternate supply fan is inoperative.

SMOKE ALTN

EQUIP COOLING

OVHT

OVERHEAD PANEL

1 23

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Pressurization System

Cabin Altitude Controls

1 Cabin Altitude MANUAL ControlSpring – loaded to center.Controls cabin outflow valve position with the Cabin Altitude Mode Selector in manual (MAN) mode.CLIMB – moves outflow valve toward open.DESCEND – moves outflow valve toward closed.

2 Outflow VALVE Position IndicatorOP – Open.CL – Closed

3 Landing Altitude (LDG ALT) IndicatorFeet.Displays selected landing altitude.

4 Landing Altitude (LDG ALT) SelectorRotate – sets landing altitude indicator.

OVERHEAD PANEL

MODE SELECTAUTO 2

AUTO 1 MAN

LDG ALT

MIN MAXDESCEND

CLIMBMANUAL AUTO RATEVALVE

OP

CL

CABIN ALTITUDE CONTROL

AUTO INOP

00340

1

2

3

4

5

6

7

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5 Cabin Altitude AUTO RATE ControlRotate –

• sets limit for cabin altitude rate of climb or descent during auto control• index mark establishes approximately 500 fpm climb and 300 fpm

descent.

6 AUTO Inoperative (INOP) LightIlluminated (amber) –

• AUTO 1 and AUTO 2 cabin altitude control functions are inoperative• MAN mode is selected.

7 Cabin Altitude MODE SELECTORAuto 1 –

• activates Auto 1 cabin altitude control for automatic operation• outflow valve positioned automatically.

Auto 2 –• activates Auto 2 cabin altitude control for automatic operation• outflow valve positioned automatically.

MAN (Manual) –• outflow valve position is controlled by the cabin altitude MANUAL

control• AUTO INOP light illuminates.

Cabin Altitude Indicators

PRESS DIFF

.125 PSITO/LDGLIMIT:

ALTITUDECABIN

01 2

2125201510 8 6

420

10

86

4

20

1000FPM X

1000FT X

PSIDIFF ALT RATE

CABIN

OVERHEAD PANEL

1

2

3

4

5

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1 Cabin Differential Pressure IndicatorPounds per square inch (psi).

2 Cabin AltitudeFeet x 1,000.

3 Cabin Altitude RateFeet per minute (fpm x 1,000).

4 Cabin Altitude LightIlluminated (red) –

• cabin altitude exceeds 10,000 feet• extinguishes when cabin altitude descends below 8,500 feet.

5 Pressure Differential (PRESS DIFF) Limit PlacardSpecifies differential pressure limitation for takeoff and landing.

Cabin Altitude (CABIN ALT) Light

1 Cabin Altitude LightIlluminated (red) –

• cabin altitude exceeds 10,000 feet• extinguishes when cabin altitude descends below 8,500 feet.

ALTCABIN

CENTER FORWARD PANEL

1

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Copyright © The Boeing Company. See title page for details.

2.10.8 D632N001-200

Bleed Air System

Bleed Air Control Panel

1 Duct Pressure (DUCT PRESS) IndicatorsPounds per square inch (psi).

2 ISOLATION SwitchOn (bar in view) – commands isolation valve to open.Off (bar not visible) – commands isolation valve to close.

3 Isolation VALVE LightIlluminated (amber) – isolation valve position disagrees with commanded position.

4 Engine (ENG) Bleed Air SwitchesOn (bar in view) – the engine bleed air valve opens when engine bleed air is available.Off (bar not visible) – valve is manually commanded closed.

DUCTLEAK

BLEED

HI STAGE

OVERHEAD PANEL

DUCTLEAK

BLEED

HI STAGE

OFF

VALVE

OFF

VALVE

BLEED AIR

ISOLATION

L ENG APU R ENG

60 80

20 0

DUCTPRESSPSI

401

2

3

4

5

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5 Engine Bleed Air OFF LightsIlluminated (amber) – engine bleed air valve is closed:

• automatically due to a system fault• the switch is OFF• the engine is not running.

6 DUCT LEAK LightsIlluminated (amber) – a high temperature bleed air leak is detected.

7 Engine BLEED LightsIlluminated (amber) – the engine bleed air temperature is excessive.

8 Engine High Stage (HI STAGE) LightsIlluminated (amber) –

• the engine bleed system pressure is excessive• the engine high pressure bleed air valve is automatically locked closed.

9 APU Bleed Air SwitchOn (bar in view) – the APU bleed air valve is automatically controlledOff (bar not visible) – commands APU bleed air valve to close.

10 APU Bleed Air VALVE LightIlluminated (amber) – APU bleed air valve position disagrees with commanded position.

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