Chapter 1

Air Conditioning & Pressurization

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SYSTEM DESCRIPTION

AIR CONDITIONING

GENERAL

Two identical air conditioning packs provide conditioned air to the aircraft. While either pack can provide sufficient air to the cabin and cockpit, the left pack is the primary source for the cockpit and the right pack is the primary source for the cabin. Pneumatic air is used for the air conditioning and pressurization systems. The normal sources of air are as follows Ground: external (not simulated) auxiliary power unit (APU), and the engines. The engines are the only source of air in flight. 

AIR CONDITIONING PACKS

GENERAL

Each pack contains two heat exchangers and an air cycle machine (ACM). Bleed air is very hot and the air cycle machine (ACM) provides cold air through mixing valves to cool the air for distribution into the aircraft. In flight a RAM air scoop located on the tail provides cooling air for the heat exchangers. On the ground the cooling air is provided by cooling fans.

AIR CONDITIONING PACK CONTROLS

SUPPLY SWITCHES

Each pack is controlled by a supply switch that that has three positions: OFF, HP BLD OFF, and AUTO

AUTO: Air is provided by the engines automatically when needed. On the ground, the associated heat exchanger cooling fan will operate.

HP BLD OFF: Same as auto except the augmentation valve that provides high pressure bleed air is closed.

OFF: No air is provided by the engines and the heat exchanger cooling fans are shut down.

APU AIR SWITCH

The air switch on the APU panel has three positions: AIR OFF, ON, AIR COND COLDER. The AIR OFF and ON selections are described in the APU section of the AIRCRAFT GENERAL chapter. The AIR COND COLDER setting forces all air through the ACM resulting in colder air leaving the ACM.

TEMPERATURE CONTROL SELECTORS AND INDICATORS

Temperature is controlled with selectors located on the air conditioning panel on the overhead. The left selector controls the temperature of the cockpit and the right selector controls the temperature in the cabin. The indicators above the selector switches show the position of the temperature control valves. As the valve opens the needle moves towards HOT and as it closed the needle moves towards COLD. The temperature range for the selectors is 65 to 85F. 

CABIN TEMPERATURE INDICATOR

The selector has two positions. In CABIN, the indicator displays the cabin temperature. One pack must be operating for the reading to be accurate. In CABIN SPLY, the indicator shows the cockpit temperature. 

AIR CONDITIONING AUTOMATIC SHUTOFF

This system is designed to shut the air conditioning off if an engine fails during takeoff. A difference in bleed pressure between left and right engine high pressure bleed systems. The system will reset if the bleed difference is equalized. The system is armed for operation when the switch is in the AUTO position and the cabin differential is below 1.3 psi. When the cabin differential is more than 1.3 psi, the system is disarmed. The OVRD position prevents the system from activating or restores normal operation after and engine failure.

EQUIPMENT COOLING

The electrical power center and equipment racks in the electrical and electronic (E&E) compartment. A radio rack fan on the left side of the E&E compartment operates continuously under normal conditions. A standby radio rack fan on the right side of the E&E compartment normally operates on the ground and shuts down in flight. In flight if the primary fan fails, the standby fan will come on to maintain circulation. There is not cockpit indication that the standby fan has replaced the primary fan. A radio rack fan switch on the air conditioning panel controls the radio rack fans and venturi valve. In the FAN position the fans operate as described above. On the ground a RADIO FAN OFF light comes on if the primary pan fails. In the air the light will come on if either fan fails. If both fans fail in flight, cooling can be maintained by placing the switch in the VENTURI position. In VENTURI, the RADIO FAN OFF light is inhibited and power to the fans is removed. When on the ground , the system will operate in the FAN mode regardless of switch position. The power source for the Primary radio fan is the LEFT DC BUS and the source for the standby fan is the RIGHT DC BUS.

AIR CONDITIONING 

CONTROLS AND INDICATORS

LOCATION: Overhead Panel

PRESSURE INDICATOR

Indicates the pneumatic pressure is available for operation of the left and right air conditioning system.

TEMP CONTROL VALVE INDICATOR

Indicates the position of the air conditioning system control valves.

    COLD - Temp control valve is closed to block hot air.

    HOT - Temp control valve is open to allow hot air into the system.

COCKPIT/CABIN TEMP SELECTOR

    AUTO - Temperature is automatically maintained by positioning the temp control valve.

    MANUAL - not simulated.

SUPPLY SWITCH

    AUTO: Air is provided by the engines automatically when needed. On the ground, the associated heat exchanger cooling fan will operate.

    HP BLD OFF: Same as auto except the augmentation valve that provides high pressure bleed air is closed.

    OFF: No air is provided by the engines and the heat exchanger cooling fans are shut down.

TEMP SELECTOR

    CABIN - the indicator displays the cabin temperature.

    CABIN SPLY - the indicator shows the cockpit temperature.

CABIN TEMP INDICATOR

Indicates Cabin or cockpit temperature in Fahrenheit

RADIO RACK SWITCH

    VENTURI - Turns of radio rack fan and opens the venturi in flight.

    FAN - Turns on primary radio rack fan and closes the venturi valve for radio rack cooling.

LOCATION: Overhead Panel

AIR CONDITIONING SHUTOFF SWITCH

    OVRD - Overrides the automatic shutdown of the air conditioning system with an engine failure

    AUTO - Both air conditioning packs shut down with an engine failure if the cabin differential pressure is below 1.3 psi.

RAM AIR SWITCH

    OFF - Normal position. Ram air valve is closed.

    ON - Ram air valve is opened to allow ram air into the right air conditioning system.

- Appears on the ground with the radio rack fan in the FAN position and the Primary fan fails. Appears in flight if both fans fail.

 

PRESSURIZATION

PRESSURIZATION SYSTEM

The pressurization system controls cabin pressure using settings on the pressurization panel. Pressure is regulated by flow of cabin exhaust air through two cabin outflow valves. The round valve (butterfly) is either open to depressurize or closed to allow pressurization. The butterfly valve position is indicated by a round yellow indicator on the pedestal. The rectangle valve regulates pressurization airflow when the butterfly valve is closed. There are two identical independent pressurization controllers and actuators. One is primary and the other is standby.

Systems Controls - STEAM & COMBO WITHOUT GPS

The pressurization panel has a switch that is used to transfer controllers. In the PRIMARY (normal) position, automatic transfer will happen if the primary controller fails. In, STBY, standby controller is active and the automatic switching is disabled.

Controller Transfer Lockout - STEAM & COMBO WITHOUT GPS

Above the controller switch there is an indicator light with TRANSFER LOCKOUT and STBY ON indications. The TRANSFER LOCKOUT light indicates that the auto switching function is inhibited due to a failure or the manual selection of the standby mode. The STBY ON light indicates the the standby mode is active due to the failure of the primary system or the manual selection of the standby mode. Anytime the STBY ON light comes on, the TRANSFER LOCKOUT will also come on. If the selector is moved from standby to primary and the system is operating normally, the TRANSFER LOCKOUT can be cleared by pressing the indicator light.

System Controls - COMBO WITH GPS & GLASS

The PRIMARY and STANDBY selections have been replaced by AUTO 1 and AUTO 2 and the TRANSFER LOCKOUT and STBY ON lights have been removed. They selector switch selects the primary system and the other serves as the standby. Should the selected system fail, the respective INOP light will illuminate and control automatically transfers to the other system. If both systems fail, the AUTO INOP indictor light comes on.

Flow Light

The FLOW light indicates that there is not enough air flow to maintain the pressurization schedule with both outflow valves fully closed.

System Settings

Destination field elevation and must be set on the pressurization panel. The range for landing elevation is -1,500 to +14,000 feet. Add two zeros to the elevation tape to read the correct altitude.

Rate Limit Knob

The rate limit knob controls the rate at which cabin will climb or descend. The maximum climb rate is from 50 to 2,000 fpm, with 700 fpm at the index. The maximum descent is from 20 to 900 fpm with 300 fpm at the index.

PRESSURIZATION INDICATORS

All aircraft have a combined cabin altitude and differential pressure indicator. The outer scale indicates the cabin altitude and the inner scale indicates the differential pressure. All aircraft also have a cabin rate indicator that displays the cabin rate of climb or descent from -1,500 fpm to +1,500 fpm.

PRESSURIZATION

CONTROLS AND INDICATORS

LOCATION: Overhead Panel

LOCKOUT RESET SWITCH

Press to reset TRANSFER LOCKOUT light

TRANSFER LOCKOUT LIGHT

Indicates the automatic transfer of the primary and standby controllers is locked out.

STBY ON LIGHT

Indicates the automatic transfer or manual selection of the standby controller.

CONTROLLER SELECTOR

    STDBY - Transfers from the primary controller to the standby controller. The TRANSFER LOCKOUT and STBY ON lights come on.

    PRIMARY - Normal. Primary controller is active.

ALTITUDE WINDOW

Add two zeros to the number to read the landing field elevation.

LANDING ALTITUDE SELECTOR 

Sets landing field elevation.

ALTITUDE SCHEDULE SCALE

Indicates the scheduled cabin altitude vs. the airplane altitude.

FLOW LIGHT

Indicates that the airflow is not enough to keep the aircraft pressurization schedule

RATE LIMIT CONTROL

Sets the cabin rate of climb and descent.

INCHES HG WINDOW

Displays inches of mercury set at the landing destination

LANDING BAROMETRIC SELECTOR

Sets landing field barometric pressure in the IN HG window.

GLASS and COMBO WITH GPS differences

AUTO INOP LIGHT

Indicates both pressurization controllers are inop

INOP LIGHT

The selected pressurization controller is inop and control has transferred to the other system.

CONTROLLER SELECTOR

    AUTO 1 - Selects number 1 controller as primary

    AUTO 2 - Selects number 2 controller as primary

                                                           

LOCATION: Overhead Panel

CABIN ALTITUDE AND DIFFERENTIAL PRESSURE INDICATOR

    OUTER SCALE - Cabin altitude

    INNER SCALE - Differential pressure. The red line is 8.32 psi.

CABIN RATE OF CLIMB INDICATOR

Indicates the rate of climb or descent in feet per minute.

- Illuminates when the cabin altitude reaches 10,000 feet.

LOCATION: Center Pedestal

OUTFLOW VALVE POSITION INDICATOR

Indicates the position of the outflow valve. Forward is closed and aft is open.

 

 

SCHEMATICS