• Pneumatic
• Air-Conditioning
• Conditioned Air Distribution
• Equipment Cooling
• Cargo Compartment Heating
• Pneumatic and
Air-Conditioning Control Panels
• Cabin Pressure Control
• Cabin Pressure Control Panels Features
PNEUMATIC
These sources supply the pneumatic manifold:
• Engine bleed air
• APU bleed air
• Ground source.
The system controls and indications reduce crew workload.
AIR CONDITIONING
The air conditioning system is a dual air cycle pack design.
The ram air system produces minimum drag.
The pack air-cycle machines have air bearings. These bearings require no regular servicing.
Pack temperature control is either automatic or manual. Automatic overtemperature protection reduces crew workload.
System maintenance does not require ladders or special stands.
A cabin air recirculation system reduces fuel consumption.
EQUIPMENT COOLING
The airplane uses two equipment cooling systems. Both systems have backup fans.
The equipment cooling system automatically configures for ground and flight operations.
CARGO COMPARTMENT HEATING
The forward cargo compartment heating is by exhaust air from the equipment cooling system.
The aft cargo compartment heating is by outflow air from the passenger cabin.
PRESSURIZATION
The cabin pressure control system uses dual, automatic, digital
pressure controllers. This increases reliability and reduces crew
workload.
Pressure controllers have BITE.
There is a manual backup pressure control system.
Independent, mechanical safety relief valves protect the airplane structure in any mode of pressure control.
Pneumatics
The pneumatic system supplies pressurized air to these systems and components:
• Engine starters
• Air conditioning packs
• Thermal anti-ice systems
• Hydraulic reservoirs
• Potable water system.
These are the sources of pneumatic power:
• External ground source
• APU load compressor
• Engine bleed air.
The APU regulates bleed air pressure from the APU load
Engine bleed air comes from the 5th or 9th stage of the high pressure compressor. The change from 5th to 9th is automatic. The pressure regulating and shutoff valves (PRSOVs) regulate engine bleed air pressure.
The precooler system cools the engine bleed air. The precooler is an air-to-air heat exchanger. It cools engine bleed air with engine fan air as the heat sink. The precooler control valve controls the flow of fan air.
The isolation valve isolates the pneumatic manifold into a left and right side when closed. This
separates the pneumatic system into
(e.g. engine starting operations). The isolation valve operation can be automatic or manual.
Pressure transmitters and a gage on the P5 panel show right and left manifold pressures.
The pneumatic system control is from the P5 panel. Improvements of controls and indications decrease crew work load.
Automatic overtemperature and overpressure protection systems protect the airplane from system malfunctions.
Overheat sensing elements near the pneumatic ducts monitor the system Pneumatics
Valve Control Valve
Check
From APU
Bleed
Wing Anti-ice
Precooler To Left Air Pressure
Transmitter
Valve Isolation
Pneumatic Ground Service Connector
Fan
Motor Operated Valve Solenoid Controlled Valve
To Starter
Pressure Regulating and Shutoff Valve High Stage Valve
To LE Slats
S
Hydraulic Reservoir Pressure Tap Potable Water Pressure Tap 2
1 1
2
Environmental Systems
Air Conditioning 737-600/700 The air conditioning system uses two independent air-cycle cooling packs, a cabin temperature control system, an air distribution system, and a recirculation system.
The system can maintain safe cabin conditions with any one subsystem inoperative.
The air conditioning packs are under the wing center section.
The air conditioning packs discharge into the mix manifold of the
The pneumatic manifold supplies compressed air to the air
conditioning packs. The flow control and shutoff valves control the air flow through the packs.
Heat exchangers and expansion through an air-cycle machine (ACM) cools pack air. The ACM is a refrigeration turbine and has air bearings. No scheduled maintenance is necessary.
On the 737-600/700, the mix valve controls pack output temperature.
This valve mixes cooled and uncooled pack air to produce
stream. The water sprays into the inlet of the ram air system.
The ram air system supplies a cooling flow of ambient air through the heat exchangers. This airstream is the heat sink for the pack system.
The ram air system inlet panels move to keep drag to a minimum. During ground operations, the ACM ram air fan pulls air through the system.
Improvements of controls and indications on the P5 panel decrease crew work load. There is manual and automatic control of pack flow rates.
Temperature control is also Air Conditioning 737-600/700
Water Spray Nozzle
Heat Exchanger Ram Air Exhaust
Ram Air Inlet
Ram Air Duct Air Cycle Machine
Water Separator Mix Muff
Pack Discharge
35F Control System
Check Valve Mix
Valve
Flow Control Control
Signals P5
Module Temp
Regulator
Ram Air System (Typical)
Control
S M
Air Cond Relays
and Shutoff Valve
(Typical)
Air Conditioning 737-800/900 The air conditioning system uses two independent air-cycle cooling packs, a digital 3-zone cabin temperature control system, an air distribution system, and a recirculation system.
The system can maintain safe cabin conditions with any one subsystem inoperative.
The location, purpose, function, and integration of the 737-800/900 system is similar to the 737-600/700 system.
The flow control and shutoff valves control air flow through the packs.
Heat exchangers and expansion
System temperature control is automatic by the pack temperature control valves and trim air valves.
Two digital pack/zone controllers operate these components:
• Temperature control valves
• Trim air valves
• The ram air actuators.
On the 737-800/900, the normal pack output temperature control is by the temperature control valve (TCV).
The standby temperature control valve can control pack output temperature if the normal system fails. The temperature control valves control the amount of pack air that does not flow through the cooling
The pack has a high pressure water extractor system. This system has a reheater/condenser/extractor assembly. This removes the water before it enters the ACM turbine.
The ram air system supplies a cooling flow of ambient air through the heat exchangers. The ram air system inlet panels move to keep drag to a minimum.
Improvement in controls and indications on the P5 panel reduce crew work load. There is manual and automatic control of pack flow rates.
Temperature control and overheat protection is automatic.
The digital pack/zone controllers Air Conditioning 737-800/900
Air Air Press Reg Valve
Stby TCV TCV
Flow Control
Ram Air Fan
Ram Air Actuator Reheater
Condenser Water Extractor Check Valve
Heat Exchanger (Typical) Trim Air Valve (Typical)
Flight Compartment Zone
Forward Pass Zone
Aft Pass Zone
ACM
Water Spray Control
Ram Air Inlet
Ram Air Exhaust Ram Air Duct S
and Shutoff Valve
Environmental Systems
Conditioned Air Distribution GENERAL
The conditioned air distribution system combines the air conditioning pack outputs with recirculated air. It then distributes the air to the flight compartment and the passenger compartment.
The mixing manifold and
recirculation components are aft of the forward cargo compartment.
The737-600/700 distribution system has these two independent
• Aft passenger compartment.
FLIGHT COMPARTMENT The flight compartment receives conditioned air from the left pack discharge.
If the left pack is off, the flight compartment receives air from the right pack and the mix manifold.
Outlets and controls in the flight compartment supply conditioned air for these functions:
• Windshield defogging
PASSENGER COMPARTMENT Conditioned air from the mix manifold moves in sidewall ducts to an overhead distribution duct above the center isle. The air comes out through these devices:
• Overhead duct nozzles
• Window diffuser outlets
• Passenger gasper outlets
• Galley ceiling gasper outlets
• Lavatory gasper outlets.
Passenger compartment air then moves through air return grills. This air then goes through a filtered Conditioned Air Distribution
Air Conditioning Packs
Diffuser Outlet
Equipment Racks Electronic Distribution
Flight Deck Controls Air Conditioning
Mix Manifold, Recirculation Fan and Filter Overhead Distribution Duct
Passenger Compartment
737-600/-700 Shown 737-800/900 Similar Sidewall Risers
(Three on 737-800/900)
(Two Fans and Filters on 737-800/900) System
(Typical)
Equipment Cooling GENERAL
Electronic equipment is air cooled.
These systems supply air to the equipment cooling system:
• The supply system
• The exhaust system.
Cooling for the most critical electronic equipment is from both cooling systems. This causes a double (push-pull) cooling system.
Cooling for less critical equipment is by one system. Electronic equipment that does not require active cooling is not included in the cooling system.
The fans, air filter, and the overboard exhaust valve are in the electronic equipment compartment. The flow detectors are in ducts in the forward equipment compartment.
Connecting ducts, equipment rack channels, headers, and plenums complete the cooling circuits.
Controls and indications are on the P5 forward overhead panel.
SUPPLY SYSTEM
The supply system pulls cooling air through a cleaner and pushes it over these components:
• Pilot primary displays (3)
• Pilot control stand
EXHAUST SYSTEM
The exhaust system pulls cooling air over these items:
• Pilot primary displays (3)
• Pilot control stand
• P6 panel
• P5 panel
• E1 and E5 racks
• Transverse rack.
The exhaust system air then discharges through an overboard exhaust valve, overboard. In flight, differential pressure causes this valve to close. These things happen when the valve closes:
• Diverts warm equipment exhaust Equipment Cooling System
Supply Fans
Exhaust Fans Flow Detectors
Supply Air Filter
Overboard Supply System
Exhaust System
Pilot Primary Pilot
E1 Rack
Transverse Rack E5 Rack
Duct (Typical)
Display (Typical)
Duct (Typical)
(E2,E3,E4) Control Stand
P5 Panel
P6 Panel
E2 E3 E4
Exhaust Valve
Environmental Systems
Cargo Compartment Heating GENERAL
The cargo compartments are not ventilated. There are sealed, fire resistant liners that prevent oxygen from sustaining a fire in a cargo compartment.
The volume of air in the cargo compartments is sufficient to sustain the life of animals with these
conditions met:
• The biomass is not too great
• The flight duration is not too long
The cargo heat system is passive. It uses the differential pressures and heat energies of the air conditioning and pressurization systems.
Cargo heating is automatic and controls, indications, or servicing are not necessary.
FORWARD CARGO COMPARTMENT
The forward cargo compartment is heated only when the airplane is in the air.
AFT CARGO COMPARTMENT
A-A B-B
Air Return Grille Diffuser Outlets Compartment
Aft Cargo Compartment Forward Cargo
Outflow
B B
A A
(Typical)
(Typical)
Valve Overboard
Cargo Compartment Heating
Exhaust Valve
Pneumatic and Air Conditioning Control Panels
GENERAL
The control panels are on the P5 forward overhead panel.
These are control panel features:
• Lighted gages
• Light plates
• Positive position toggle switches and selector knobs
• System condition and caution lights.
PNEUMATIC CONTROLS Toggle switches control these functions:
System indication lights show these conditions:
• Bleed trip off
• Wing-body overheats (duct leaks)
• Dual bleed
• Loss of equipment cooling.
Push-button switches control:
• Resets of trip off conditions
• Wing-body overheat tests.
AIR CONDITIONING CONTROLS 737-600/700
Switches control these functions:
• Pack flow scheduling
• The right recirculation fan
Gages show the mix valve position.
A temperature gage and source selector show the system temperatures.
System lights show these conditions:
• Pack trip off
• Duct overheats
• Ram door position.
AIR CONDITIONING CONTROLS 737-800/900
The higher capacity three-zone temperature control system of the 737-800/900 uses these additional controls:
• Left recirculation fan switch
• Three temperature selectors
AIR TEMP
Pneumatic and Air Conditioning Control Panels
737-600/700
TRIM AIR
CONT CAB FWD CAB AFT CAB
OFF OFF OFF
OFF a OFF a EQUIP COOLING
EXHAUST NORM
ALTN
DUAL BLEED FULL OPENRAM DOOR
TRIP OFFPACK
OVERHEAT WING-BODY
BLEED TRIP OFF
RAM DOOR FULL OPEN
40
ICE ANTI
ICE
HIGH HIGH
AUTO
RECIRC FAN
OVHT
DUCT OVERHEAT
COOL
COOLOFF MANUAL PASS AIR MIX
VALVE AIR MIX
VALVE
AIR TEMP
CONT CABIN PASS CABIN
200 120 160
40 F 80
TEMP.
Air Conditioning Panel Equipment Cooling
Panel
737-800/900
Cabin Temperature Panel P5 Forward Overhead
Panel
CONTCAB
AFT AFT
R
COOLOFF MANUAL
WARM WARM AUTO
TRIP OFFPACK
OVERHEAT WING-BODY
BLEED TRIP OFF
DUCT OVERHEAT
SUPPLY
Environmental Systems
Cabin Pressure Control NORMAL OPERATION
The pressurization system controls the rate of air released from the cabin. The position of the outflow valve controls this rate.
The cabin pressurization system maintains a safe, comfortable cabin pressure altitude at all times. Under normal operations, cabin pressure altitude is never more than 8,000 feet.
The pilots can control airplane
Two digital controllers are in the EE compartment. The controllers have LRU BITE. They use inputs from these to control cabin pressure:
• P5 panel settings
• Stall management computers
• Air data computers
• Aft outflow valve position transducer.
In the automatic modes (auto and alternate), the controllers
automatically schedule cabin pressurization for all phases of flight.
If both controllers fail, the pilot can control the valve manually.
FAIL-SAFE DEVICES
If the systems fail, these valves protect the airplane structure from excessive pressure differentials:
• Positive pressure relief valves (2)
• Negative pressure relief valve
• Cargo compartment blowout panels.
ALTITUDE WARNING
A cabin altitude warning system tells the crew when the cabin pressure altitude goes to 10,000 feet. This system activates by a switch on the Cabin Pressure Control
Pressurized Area
Negative Relief Valve Outflow Valve
Pressure Relief P5 Forward Overhead
Panel
Valves (2) Pressure Equalization
Blowout Panels
Digital Cabin Pressure
Outflow Valve Pressurization Control Panel
Manual Signal
Auto Signal
EV LA V MANUAL AUTO
LAND ALT FLT ALT
AUTOALTN MAN
Valves (Typical) Digital Cabin Pressure Controllers (2)
MANUALg a DESCENTa g FAIL
AUTO OFF SCHED ALTN
Positive
Controller (2)
Cabin Pressure Control Panels GENERAL
The pressurization control panels are on the P5 forward overhead panel.
These are the control panel features:
• Lighted indicators
• Light plates
• Selectors
• LCD numerical displays
• Toggle switch
• Push-button switch
• System indication and warning lights.
PRESSURIZATION CONTROLS There are controls for these
LCD digital displays show these settings:
• Flight altitude
• Landing altitude.
There is a flight altitude/cabin altitude conversion placard below the controls. Manual calculations are not necessary.
A takeoff pressure differential limitation placard is for reference during manual operations.
A toggle switch is for control of the outflow valve during manual operations.
A dual-needle indicator shows this data:
A cabin rate of climb indicator shows this data:
• Rate of cabin ascent
• Rate of cabin descent.
The push-button altitude horn cutout switch stops the 10,000 ft warning horn.
System indication and warning lights give these indications:
• Automatic control channel failure
• Aborted takeoff pressure scheduling if the airplane is off the scheduled descent
• Alternate channel automatic control of the outflow valve
• Manual control mode of the Cabin Pressure Control Panels
P5 Forward Overhead Panel
Cabin Pressure Control Panels
FL260 FL320 FL410 8000 6000 4000 FL220 LAND ALT
CAB ALT 2000
<FL160 FLT ALT
E
FLT ALT
ALTN
LAND ALT
DESCENT
PRESS DIFF LIMIT: TAKE-OFF & LDG .125 PSI
CUTOUT
X 1000 FEET
DN UP
g
a g
FAIL a AUTO OFF SCHED
MANUAL ALTN