C90 Pressurisation / Envirnomental Systems Flashcards
Max Pressure Differential
The Pressurisation systems utilised engine bleed air to pressurise the aircraft cabin to 5.0 ±0.1 PSI.
This will give a cabin altitude of
6,000ft at 20,000ft altitude
12,000ft at 30,0000ft altitude
Flow control unit:
Located in the nacelle of each engine controls the pressure of the bleed air and mixes in ambient air in order to provide an air mixture suitable for the pressurization function
Air to Air Heat Exchanger
Utilises air from Wing Root Ram Air intake to condition bleed air to a temperature suitable for use by the Pressurisation / Environment Control System
Outflow Valve:
Regulates pressure with the cabin and rate of cabin pressure change by modulating Inflow vs Outflow of the pressurisation system. The Outflow valve is connected to and controlled by the Pressurisation Controller
Vacuum Safety Valve:
Provides pressure relief (in the event of outflow valve malfunction), depressurization, and to keep the pressure vessel unpressurised while on the ground It is not connected to the pressurization controller, it is set to operate slightly below the max differential pressure to prevent inadvertent operation
Negative Pressure Relief Valve:
A negative pressure relief function is provided to prevent outside atmospheric pressure from exceeding cabin pressure by more than 0.1 psi during rapid descents
The NPRV is a spring actuated Poppet valve that can operate independent of the Pressurisation and electrical systems
Ram Air Ventilation :
Ram air ventilation is available during unpressurised flight to provide cabin ventilation. Ram Air is obtained via the ram scoop on the front left nose of the aircraft, In normal operations a flapper door in the scoop is held closed by electromagnet, maintaining pressure vessel integrity
In (normal) unpressurised flight at more then 180kts the Ram Scoop flapper door is opened via dynamic pressure allowing fresh air into the cabin.
In unpressurised flight with the cabin Dump valve open the electromagnet is depowered and the door is able to be opened at any speed maintain to cabin ventilation
Aircraft Altitude Selector
Indicates aircraft maximum pressure altitude without causing the cabin pressure altitude to climb above the value selected on the outer scale (CABIN ALT) of the dial
Both scales rotate together when the cabin altitude selector is turned
Max cabin altitude from -1000 to +10000ft
Rate of change from 220 to 2000fpm , The 12 o’clock position ≈ 500fpm
**PRESS ** - Top Left Hand Corner
Selection of PRESS on the Cabin Pressure Controller will close the safety valve thus pressurising the cabin
Pressurisation System Operations
Climb
1/ Adjust the cabin altitude selector so the ACFT ALT is 1000ft above the planned cruise pressure altitude
2/ CABIN ALT must indicate at least 500ft above the T/O field pressure altitude, prior to T/O to prevent T/O Cabin Bump
3/ Set the rate control selector at the 12 o’clock position for most comfortable cabin rate of climb
4/ As the airplane climbs, the cabin pressure altitude climbs at the selected rate of change until the cabin reaches the selected pressure altitude
Pressurisation System Operations
Descent
1/ Set CABIN ALT to 500ft above the landing field pressure altitude
2/ If a lower cabin altitude (than airplane altitude) is not selected a depressurisation will occur on descent
3/ Control the airplane rate of descent so that the airplane altitude does not catch up with the cabin pressure altitude
4/ Monitor cabin descent indicator.
Otherwise a negative pressure situation may develop
5/ Once the airplane reaches the cabin pressure altitude, the negative pressure relief function opens the
Max Differential Operations
Cabin pressure will be released if the airplane climbs to an altitude higher than the ACFT ALT, so as to maintain 5.0 psi, thus operating the outflow and safety valves
(Max Differential Operations)
If the cabin altitude reaches 12500ft, a sensing switch will close, causing
master warning
If the flight plan calls for an altitude change of 1000ft or more, reselect the new altitude + 1000ft on the CABIN ALT dial, so as to maintain 5 psi
Cabin Heating:
On ground
Electrical Heat provides initial warm-up of the cabin
Cabin Heating:
In Flight
Bleed air is delivered to the environment bleed air duct, the ambient air valve is opened, and outside air is mixed with the engine bleed air in the flow control unit to provide heat.
In low ambient air conditions or low power settings where bleed may not be sufficient to providing heating the electric heat can be used to supplement heating. Only 4 of the heater elements will be available inflight for this function.
Cabin Cooling:
Bleed air is passed through the heat exchanger in the wing centre section this is then passed to a Refrigerant unit located in the aircraft nose. The Freon Cycle system cools the Heat exchanged air and distributes through the cabin louver and gasper valve network
This conditioned air can be “trimmed” to warmer temperatures by mixing non condition, heat exchanged air to achieve desired cabin temperature.
Temperature Control:
Automatic Mode Control
The automatic temperature control modulates the bypass valves to allow heated air to bypass the air-to-air heat exchangers in the centre wing sections. Temperature can be selected via the ECS sub panel
