AIRCRAFT SYSTEMS: AIR CONDITIONING / PRESSURIZATION / VENTILATION Flashcards
It provides continuous air renewal and maintains a constant, selected temperature in the following three zones :
COCKPIT, FWD CABIN, AFT CABIN. These three zones are independently controlled.
Air is supplied by the pneumatic system, via:
‐ Two pack flow control valves,
‐ Two packs,
‐ The mixing unit, which mixes the air that comes from the cabin and the packs.
In an emergency, a ram air inlet can provide
ambient air to the mixing unit.
Temperature regulation of the temperature is ensured by
a zone controller and two pack controllers, or two Air Conditioning System Controller (ACSC)
Temperature regulation is optimized via
the hot air pressure regulating valve, and the trim air valves that add hot air, tapped upstream of the packs, to the air coming from the mixing unit.
During cruise, the cabin crew can modify each cabin zone temperature that is selected from the cockpit, with a limited authority of
± 2.5 °C.
The two AIR CONDITIONING PACKS operate automatically and independently of each other. Pack operation is controlled by signals coming from
the pack controller or the Air Conditioning System Controller (ACSC)
Warm pre-conditioned bleed air enters the cooling path via the pack flow control valve, and is ducted to
the primary heat exchanger.
PACK FLOW CONTROL VALVE is ___-operated and ___-controlled
pneumatically / electrically
PACK FLOW CONTROL VALVE regulates the air flow in accordance with signals received from
the pack controllers or the ACSC.
In the absence of air pressure, a spring keeps the valve closed.
The valve closes automatically in case of
pack overheat (on ground only), engine start, or operation of the fire or ditching pushbutton.
EMERGENCY RAM AIR
An emergency ram air inlet ventilates the cockpit and cabin to
remove smoke, or if both packs fail.
The emergency ram air inlet valve is controlled by
the RAM AIR pushbutton on the AIR COND panel.
This pushbutton opens the ram air valve, provided that ditching is not selected.
When the RAM AIR pushbutton is ON : The outflow valve opens about 50 %, provided that it is under automatic control and ΔP is less than 1 PSI. The outflow valve does not automatically open if
it is under manual control, even if ΔP is less than 1 PSI. If ΔP is greater than 1 PSI, the check valve located downstream the ram air door will not open, even if the ram air door has been selected open. No airflow will then be supplied.
MIXER UNIT mixes cold fresh air from the packs with the cabin air being recirculated through
recirculation fans.
The mixer unit is also connected to the emergency ram air inlet and the low pressure ground inlets.
HOT-AIR PRESSURE-REGULATING VALVE regulates the pressure of
hot air, tapped upstream of the packs.
It is pneumatically-operated and electrically-controlled from the HOT AIR pb-sw on the AIR COND panel.
The ACSC 1 regulates this valve.
In the absence of air, a spring keeps the valve closed.
HOT-AIR PRESSURE-REGULATING VALVE closes automatically, if:
‐ Both lanes of ACSC 1 or ACSC 2 fail, or
‐ The duct overheats, or
‐ At least two trim air valves fail.
The valve remains operative, even if either the forward or aft cabin trim air valve fails.
TRIM AIR VALVES are electrically-controlled by the zone controller or the ACSC . A trim air valve, associated with each zone, adjusts
the temperature by adding hot air.
The cockpit trim air valve is controlled by the ACSC 1 , and the cabin trim air valves are controlled by the ACSC 2 .
Temperature regulation is automatic and controlled by
one zone controller and two pack controllers, or the ACSC .
The actual temperature is measured by sensors:
‐ In the cockpit, for the cockpit zone;
‐ for the cabin ___
In the lavatory extraction circuit and galley ventilation system
OPTIMIZED TEMPERATURE REGULATION
The temperature selection range is from
18 °C to 30 °C
AIR CONDITIONING SYSTEM CONTROLLERS regulates the temperature of its associated pack, by modulating
the bypass valve and the ram air inlet flap.
The ram air inlet flap closes during takeoff and landing to avoid the ingestion of foreign matter.
During takeoff, the ram air inlet flap closes when takeoff power is set, and the main landing gear struts are compressed.
During landing, it closes as soon as the main landing gear struts are compressed, as long as speed is at or above
70 kt.
It opens 20 s after the speed drops below 70 kt.
PACK FLOW CONTROL
Whatever the crew selects, the system delivers higher flow for any of the following circumstances:
‐ In single-pack operation,
‐ When the APU is supplying bleed air.
ENGINE PRESSURE DEMAND
When the cooling demand in one zone cannot be satisfied, if the bleed pressure is too low, the air conditioning system controller sends a pressure demand signal to both Engine Interface Units (EIU) to increase
the minimum idle and to raise the bleed pressure.
APU FLOW DEMAND
When the APU bleed valve is open, the air conditioning system controller signals the APU’s Electronic Control Box (ECB) to increase
the APU flow output when any zone temperature demand cannot be satisfied.
AIR CONDITIONING - SYSTEM OPERATION UNDER FAILURE CONDITION
Each controller is comprised of two lanes. One lane controls the system,
the other takes over full control, in case of an active lane failure.
AIR CONDITIONING - SYSTEM OPERATION UNDER FAILURE CONDITION
ONE LANE FAILURE
No effect, as the second lane takes over.
AIR CONDITIONING SYSTEM CONTROLLERS
BOTH LANES FAILURE
The related pack is lost, and the hot air pressure-regulating valve and associated trim air valves close.
AIR CYCLE MACHINE FAILURE
If the Air Cycle Machine (ACM) fails (compressor/turbine seizure), the affected pack may be operated in
heat exchanger cooling mode.
HOT AIR PRESSURE REGULATING VALVE FAILURE
Failed open : No effect.
Failed closed :
Optimized regulation is lost. Trim air valves are driven to the fully closed position.
Pack 1 controls the cockpit temperature to the selected value and pack 2
controls the cabin temperature (FWD and AFT) to the mean value of the selected temperatures.
TRIM AIR VALVE FAILURE
Optimized temperature regulation of
the corresponding zone is lost.
HOT AIR pb FAULT :
The FAULT light comes on amber, along with an associated ECAM caution, when
duct overheat is detected.
The valve and trim air valves close automatically.
PACK pb-sw ON :
The pack flow control valve is automatically-controlled.
Pack flow control valve opens, except in the following cases:
‐ Upstream pressure below minimum
‐ Compressor outlet overheat
‐ Engine start sequence:
‐ FIRE pb, of the engine on the related side, is pressed
‐ Ditching is selected.
PACK pb-sw
On ground, reopening of the pack flow control valves is delayed for ___ to avoid a supplementary pack closure cycle during second engine start.
60 s
PACK FLOW selector
‐ Permits the selection of pack valve flow, according to the number of passengers and ambient conditions (smoke removal, hot or wet conditions)
LO (___) – NORM (100 %) – HI (___)
80 % / 120 %
PACK FLOW selector
‐ Manual selection is irrelevant in single pack operation, or with APU bleed supply. In these cases, ___ is automatically selected
HI
PACK FLOW selector
‐ If LO is selected, the pack flow can be automatically selected up to ___ when the cooling demand cannot be satisfied.
100 %
RAM AIR pb (guarded)
If the DITCHING pb, on the CABIN PRESS panel, is in normal position:
‐ The emergency ram air inlet opens
‐ If Δp ≥ 1 PSI: The outflow valve control remains normal. No emergency ram air
flows in
‐ If Δp < 1 PSI: The outflow valve opens to about 50 % when under automatic control.
It does not automatically open when it is under manual control. Emergency ram airflow is directly supplied to the mixer unit.
CAB FAN pb ON :
The two cabin fans are on.
The cabin pressurization system has four general functions:
Ground function
Prepressurization
Pressurization in flight
Depressurization