108.1 Discuss the purpose of the following:

a. Aircraft Cabin pressurization

Flying at altitudes up to 37,000 feet, places humans in surroundings in which he cannot survive without artificial aids. At altitudes above 10,000 feet breathing becomes very rapid and above 25,000 feet unconsciousness occurs, quickly followed by death. The higher the altitude the less the amount of oxygen per unit of volume of air, therefore oxygen intake is reduced. Pressurizing the air keeps the oxygen level at a breathable level for passengers and crew. Pressurized air for the cabin is derived from the engine compressors. The air is processed by the pneumatic and air-conditioning systems before entering the cabin. The automatic cabin pressure control system will maintain pressure within set parameters to a maximum of approximately 7.46 pounds per square inch differential pressure.

b. Air Conditioning

There are different temperatures at various altitudes and also aerodynamic heating, engine heat, solar heat, and heat from electrical units. Air conditioning is needed to maintain reasonable temperatures for human comfort and aircraft operation. The aircraft has 2 air-conditioning systems designed for use on the ground or in-flight. The right system operates from the right engine engine bleed air and supplies pressurized conditioned air to the cabin. The left system operates from the left engine bleed air and supplies conditioned air to the flight compartment. Either system can supply the requirements of both components.

108.2 Discuss the De-Ice system for inclement weather procedures.

Ice on the airframe decreases lift and increases weight, drag, and stalling speed. In addition, the accumulation of ice on exterior movable surfaces affects the control of the aircraft. The possibility always exists that engine icing may result in loss of power. The total effect of aircraft icing is loss of aerodynamic efficiency; loss of engine power, loss of proper operation of control surfaces, brakes, and landing gear. Loss of aircrew's outside view; false flight instrument indications and possible loss of radio communication. Should any coating of frost be present on the lower wing surface, the captain must be advised. Immediately following a snowfall, the aircraft should be cleared of all snow to prevent melting snow from freezing to the surface and interior areas of the aircraft to which water may flow. Heated deicing solutions may be used effectively to remove snow and ice from aircraft surfaces. Loosened ice should be removed from surfaces immediately. There are several warnings and cautions associated with de-icing. Some of these are:

1. Ingestion of deicing solutions into operating engines used as environmental control air sources can cause smoke and vapors to enter the cabin area.

2. When de-icing avoid excessive fluid flow. Use special care to prevent flushing of resultant slush into control areas forward of the control surfaces.

3. Dilution of deicing solutions with melted snow water could result in a weak mixture which may refreeze. This can create an icing condition more difficult to remove.

4. If it is suspected that snow, slush or ice is present in seal or control areas forward of control surfaces, this must be cleared prior to powering up the hydraulic systems. Failure to do this could result in serious damage to the control surfaces.

5. Never spray deicing fluid or water on or into the pitot tubes, static ports or heater cabin intakes, or against the trailing edge of the wings or control surfaces.

6. Accumulations of deicing fluids and solutions should be removed before from engines or APU before starting. These solutions can cause internal damage to the engines and APU hot sections.

7. When heated water is used for snow and ice removal, deicing fluid should be applied to the surface immediately following to prevent refreezing.

8. Avoid temperatures in excess of 200 degrees F when heating aircraft surfaces and or conpartments when using heated air. High temperatures on cold windows can crack windows.

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