Air Systems - Air Conditioning Show Schematic only.

Amendment: QRH again recommends FL350 in the event of PACK OFF.

Introduction

Air conditioning system Compartment Temperature Inoperative Compartment Temperature Inoperative Compartment Temperature Inoperative Compartment Temperature Controller Compartment Temperature Controller Compartment Temperature Controller Trim Air Switch Recirculation Fan Switches Pack Reset Switch Pack Reset Switch Pack Control Selectors Pack Control Selectors Equipment Cooling External Ground Conditioning

The air-conditioning system supplies conditioned bleed air and recirculated cabin air at a controlled temperature throughout the airplane, by processing bleed air from the airplane Pneumatic System (Engines or APU) or from a ground source.

The system supplies conditioned air to the flight deck shoulder heaters [and] ventilation for the cabin:

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 Packs

Two identical air conditioning packs cool bleed air from the airplane Pneumatic System (Engines or APU) or high pressure air from a ground source. Bleed air is pre-cooled before entering the pack.

Pack Controllers

The packs are controlled by two identical Pack Controllers. Pack output is automatically increased (High Flow) during high pack demand periods (to compensate for a failed pack or recirculation fan) or limited during high bleed air demands (such as with an engine inoperative).

Positioning the selector to AUTO or STBY sends an open signal to the Pack Valve.

Pack Valves

The Pack Valve is a flow control valve and requires air pressure to open. When open, the valve limits air flow to a scheduled rate based on airplane altitude.

Air Conditioning Automatic Mode

With 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.

Conditioned air from the packs flows into a common manifold where it mixes with air from two recirculating fans. The mixed air is then ducted into the temperature controlled compartments of the airplane.

Pack High Flow

Certain operating conditions require the pack(s) to provide higher than normal air flow for adequate air conditioning and pressurization. This is accomplished by a pack high air flow system. The system is automatic and armed for operation at all times.

The pack high flow system controls the pack valve to open to a second schedule and provide more airflow for:

  • During ground operation whenever the APU or ground source is supplying air for air conditioning (both packs HIGH).
  • If one pack is INOP.
  • If a recirculation fan is INOP.

The pack high flow system is inhibited when:

  • Wing anti-ice is ON and only one engine is supplying bleed air
  • an Engine is INOP
  • Flaps are not UP
  • aft cargo compartment ARMED switch pushed

When a pack is operating in high flow, the displayed EPR limit for the associated engine is automatically reduced.

Air Conditioning Standby Mode

With the Pack Selector in the Standby mode, pack output temperature is determined by the position of the Pack Selector:

Ground Conditioned Air Operation

When a ground source of conditioned air is available, it may be used to supply conditioned air directly to the cabin air distribution system, eliminating the need for pack operation. Air from the ground source enters the left air conditioning manifold and is routed through the mix manifold to the cabin distribution ducts.

Pack Non-Normal Operation

Pack Control, zone temperature control, cabin air recirculation, fault detection and overheat protection are automatic.

Pack INOP

Pack Inop

When an automatic control fault or a pack overheat is detected, the pack automatically shuts down. The pack INOP light illuminates and the EICAS advisory message L/R PACK TEMP displays.


PACK OFF

Pack Off

The PACK OFF Light illuminates and the EICAS message L/R PACK OFF displays whenever the Pack Valve is Closed.

The Pack Valve will Close if:

QRH Limit flight to FL350 or below to maintain normal cabin altitude (due to mass airflow requirements).

Packs Off Take-Off

During a Packs Off Take-Off, both engine Bleed Air Valves may close due to low air demand, with associated L/R ENG BLEED OFF advisories.

Air Distribution

Conditioned 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.

Recirculation Fans

The Left Recirculation fan draws air through the Forward Electrical/Electronic Equipment Cooling System, main instrument panels, overhead panels and Weather Radar and returns it into the mix manifold.

The Right Recirculation fan draws air from the passenger cabin into the forward cargo compartment sidewalls. From there it is blown by the recirculation fan into 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 after landing to reset this valve.

Recirc Fan INOP

The Recirculation Fan INOP Light illuminates and the EICAS advisory message L/R RECIR FAN displays whenever a Recirculation Fan fails or is not operating. A slight increase in fuel consumption occurs for each fan that is OFF.


Compartment Temperature Control

Compartment Temperature Control.

The airplane is divided into three (-200) or four temperature control compartments:

The Pack Controllers regulate the pack output air temperature to satisfy the temperature requirement of the compartment requiring the coolest air.

Trim Air

Hot Trim Air from the bleed air system (obtained downstream of the Pack Valves) is added through Trim Air Valves to control the temperature in each of the other compartments.

Each of the three (-200) or four temperature control compartments has an associated Temperature Controller which modulates Trim Air to satisfy the increased temperature requirements.

Compartment Temperature INOP

Inop A compartment INOP light illuminates and the EICAS advisory message FLT DECK TEMP, FWD CABIN TEMP, MID CABIN TEMP, AFT CABIN TEMP displays to indicate:

Temperature Control with Loss of Trim Air System

Trim Air Off

During operation with the Trim Air System OFF, the Cabin Temperature Controller attempts to maintain all compartments at an average temperature (24°C). The Trim Air OFF Light illuminates and the EICAS advisory message TRIM AIR displays when the Trim Air switch is OFF.

Shoulder and Foot Heaters

Flight 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.

Zonal Dryer

Zonal Dryer.

AMM The Zonal Drying system keeps the humidity in the crown area at a level where it will reduce the condensation on the fuselage skin inner surface and stop water accumulation in insulation blankets. By creating differential vapor pressure in the intermediate space on the aircraft the crown area and subsequently the side walls will dry out.

The system consists of one Zonal Dryer installed behind the AFT Cargo compartment, close to the Potable Water tank. The air is led to and from the Zonal Dryer via three lightweight ducting systems.

Pressurization