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Questions and Answers
What are the sources of air supply described in section 11.4.1?
What are the sources of air supply described in section 11.4.1?
engine bleed, APU, ground cart
Which of the following is considered a source of air supply?
Which of the following is considered a source of air supply?
The engine bleed system is used as a source of air supply in aircraft.
The engine bleed system is used as a source of air supply in aircraft.
True
What do the knowledge level indicators in Category A, B1, B2, and C Aircraft Maintenance Licence signify?
What do the knowledge level indicators in Category A, B1, B2, and C Aircraft Maintenance Licence signify?
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What is the basic objective for Level 1 knowledge?
What is the basic objective for Level 1 knowledge?
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Describe the objectives for Level 2 knowledge.
Describe the objectives for Level 2 knowledge.
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What does Level 3 knowledge entail?
What does Level 3 knowledge entail?
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Which aircraft systems use pneumatic power?
Which aircraft systems use pneumatic power?
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The APU can supply bleed air to all pneumatic systems in aircraft.
The APU can supply bleed air to all pneumatic systems in aircraft.
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What provides compressed air for cabin pressurisation in smaller turboprop aircraft?
What provides compressed air for cabin pressurisation in smaller turboprop aircraft?
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In case of failure of both packs, an emergency ram air flap can be opened for A/C ventilation or _______ removal.
In case of failure of both packs, an emergency ram air flap can be opened for A/C ventilation or _______ removal.
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What drives the centrifugal compressor in an air-cycle machine?
What drives the centrifugal compressor in an air-cycle machine?
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What is the purpose of the water separator in an air-cycle machine?
What is the purpose of the water separator in an air-cycle machine?
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Air-cycle machine turbines run at very low speeds compared to other aircraft components.
Air-cycle machine turbines run at very low speeds compared to other aircraft components.
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Air-bearing air cycle machines use ____ to support the shaft instead of oil bearings.
Air-bearing air cycle machines use ____ to support the shaft instead of oil bearings.
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What is the function of an air conditioning system in an aircraft cabin?
What is the function of an air conditioning system in an aircraft cabin?
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Air-Cycle cooling systems in aircraft consist of expansion turbines, air-to-air heat exchangers, and various valves.
Air-Cycle cooling systems in aircraft consist of expansion turbines, air-to-air heat exchangers, and various valves.
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What is the primary component of each air conditioning pack assembly?
What is the primary component of each air conditioning pack assembly?
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The Flow Control Shut-Off Valve (FCSOV) controls the flow of ________ bleed air to the primary heat exchanger.
The Flow Control Shut-Off Valve (FCSOV) controls the flow of ________ bleed air to the primary heat exchanger.
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What type of unit is the cabin sensor?
What type of unit is the cabin sensor?
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Where is the temperature controller normally located?
Where is the temperature controller normally located?
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The air temperature selector is a ______ located in the cabin.
The air temperature selector is a ______ located in the cabin.
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The Wheatstone bridge remains balanced when the temperature-sensing element and the cabin selector knob resistance values are proportional.
The Wheatstone bridge remains balanced when the temperature-sensing element and the cabin selector knob resistance values are proportional.
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What purpose does the bypass valve serve in the water separator and coalescer bag system?
What purpose does the bypass valve serve in the water separator and coalescer bag system?
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Which type of water extractor requires no routine maintenance like changing the coalesce bag?
Which type of water extractor requires no routine maintenance like changing the coalesce bag?
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A mixing chamber allows hot air to bypass the air cycle machine.
A mixing chamber allows hot air to bypass the air cycle machine.
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The __________ system controls the quantity of outer ambient air that flows through the heat exchangers.
The __________ system controls the quantity of outer ambient air that flows through the heat exchangers.
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Match the following components with their roles in the vapour cycle air conditioning system:
Match the following components with their roles in the vapour cycle air conditioning system:
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When would the emergency ram-air valve or door be opened?
When would the emergency ram-air valve or door be opened?
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How does the air conditioning distribution system supply conditioned air to the flight compartment and passenger cabin?
How does the air conditioning distribution system supply conditioned air to the flight compartment and passenger cabin?
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The temperature changes are made by the mixing valve with signals from the ______ controller.
The temperature changes are made by the mixing valve with signals from the ______ controller.
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What are expansion bellows used for in the duct system?
What are expansion bellows used for in the duct system?
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The recirculation air filters remove microscopic particles to ensure clean air in the cabin.
The recirculation air filters remove microscopic particles to ensure clean air in the cabin.
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Match the following components with their function in the temperature control system:
Match the following components with their function in the temperature control system:
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How is the compressor in electric motor-driven compressors controlled?
How is the compressor in electric motor-driven compressors controlled?
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What is the main purpose of the condenser in a vapour-cycle air-conditioning system?
What is the main purpose of the condenser in a vapour-cycle air-conditioning system?
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Externally balanced thermal expansion valves use a pressure tap from the outlet of the evaporator to help balance the diaphragm.
Externally balanced thermal expansion valves use a pressure tap from the outlet of the evaporator to help balance the diaphragm.
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The receiver-dryer is located in the ________ side between the condenser and the expansion valve.
The receiver-dryer is located in the ________ side between the condenser and the expansion valve.
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Match the thermal expansion valve type with its description:
Match the thermal expansion valve type with its description:
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Study Notes
Category B1 Licence
- The Category B1 Licence is related to Aeroplane Systems, specifically Pneumatics.
Knowledge Levels
- Knowledge levels are indicated by the allocation of knowledge levels indicators (1, 2, or 3) against each applicable subject.
- Category A, B1, and B2 applicants must meet the basic knowledge levels for their respective categories.
- Category C applicants must meet either the Category B1 or Category B2 basic knowledge levels.
Level 1 Objectives
- The applicant should be familiar with the basic elements of the subject.
- The applicant should be able to give a simple description of the whole subject using common words and examples.
- The applicant should be able to use typical terms.
Level 2 Objectives
- The applicant should have a general knowledge of the theoretical and practical aspects of the subject.
- The applicant should be able to apply their knowledge in a practical manner.
- The applicant should be able to understand theoretical fundamentals of the subject.
- The applicant should be able to give a general description of the subject using typical examples.
- The applicant should be able to use mathematical formulae in conjunction with physical laws describing the subject.
- The applicant should be able to read and understand sketches, drawings, and schematics describing the subject.
Level 3 Objectives
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The applicant should have a detailed knowledge of the theoretical and practical aspects of the subject.
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The applicant should be able to combine and apply the separate elements of knowledge in a logical and comprehensive manner.
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The applicant should know the theory of the subject and its interrelationships with other subjects.
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The applicant should be able to give a detailed description of the subject using theoretical fundamentals and specific examples.
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The applicant should understand and be able to use mathematical formulae related to the subject.
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The applicant should be able to read, understand, and prepare sketches, simple drawings, and schematics describing the subject.
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The applicant should be able to apply their knowledge in a practical manner using manufacturer's instructions.
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The applicant should be able to interpret results from various sources and measurements and apply corrective action where appropriate.### Air Supply (11.4.1)
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The purpose of the air supply system is to provide compressed air to various aircraft systems.
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The pneumatic system supplies compressed air (low to medium pressure – high flow) to several aircraft systems, including:
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Engine start systems
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Air conditioning and pressurisation systems
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Nitrogen generation systems
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Engine inlet cowl and wing anti-ice systems
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Water tank pressurisation system
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Hydraulic reservoir pressurisation system
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The air supply sources include:
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Engine bleed air
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Auxiliary power unit (APU)
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Electric cabin air compressors
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Centrifugal cabin compressor
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Turbo charger
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Jet pump
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Ground supply cart
Engine Bleed Air
- Engine bleed air is taken from the engine compressor to be used for air conditioning and cabin pressurisation.
- Bleed air is taken from the compressor in one or two places at the Low-Pressure (LP) and High-Pressure (HP) stage.
Air Conditioning (11.4.2)
- The air cycle system is used for air conditioning and cabin pressurisation.
- The air cycle system components include:
- Flow control shut-off valve
- Primary and secondary heat exchangers
- Primary heat exchanger
- Secondary heat exchanger
- Air cycle machine turbine unit
- Air-cycle machine construction
- Low-limit anti-ice valve
- Cabin temperature control valves
- Air-cycle machine temperature control valve
- Air-mixing valve
- Water separator
- High-pressure water extractor
- Mixing chamber
- Ram air door
- Vapour cycle machines are also used for air conditioning and include:
- Vapour cycle machine compressor
- Vapour cycle machine condenser
- Vapour cycle machine receiver dryer
- Vapour cycle machine thermal expansion valves
- Vapour cycle machine evaporator
- Vapour cycle machine refrigerant
- Air distribution systems include:
- Cabin air supply sources
- Cabin air distribution
- Cabin air filters
- Cabin airflow control
- Cabin air recirculation system
- Gasper air
Pressurisation (11.4.3)
- Pressurisation systems maintain a safe internal pressure within the aircraft.
- Pressurisation modes of operation include:
- Climbing and descending
- Cruising
- Emergency pressurisation
- Cabin pressurisation control systems include:
- Pressurisation air sources
- Pressurisation controller indications
- Cabin altimeters
- Rate-of-change (vertical speed) indicators
- Differential pressure indicator
- Cabin rate of change control
- Pneumatic cabin pressurisation systems include:
- Pneumatic pressure controller
- Pneumatic system operation
- Electronic cabin pressurisation systems include:
- Electronic pressure controllers
- Electronic control operation
- Negative pressure relief valve
- Pressurisation indication and warning systems include:
- Pressurisation indication and warning systems operation
- Electronic pressurisation system fault finding
Safety and Warning Devices (11.4.4)
- Safety and warning systems include:
- Bleed air supply and air conditioning system protection
- Temperature controller
- Multi-zone climate controlled indication
- Cabin pressurisation safety and warning systems
- Pressurisation system protection
- Cabin pressurisation controls
- Emergency air supply during unpressurised flight
- Ditching protection includes:
- Emergency oxygen system
- Emergency air supply system
Fire Protection (11.8)
- Fire protection systems include:
- Fire and smoke detection and warning systems
- Fire extinguishing systems
- Fire and smoke detection and warning systems include:
- Fire/overheat detection systems
- Spot-type fire/overheat detection systems
- Continuous-loop (fire wire) fire/overheat system
- Overheat detection system operation
- Smoke detection systems
- Fire extinguishing systems include:
- Fire extinguishing systems
- Engine fixed fire extinguishers
- Lavatory fire extinguishing
- APU fire extinguishing system
- Fire extinguishing system - precautions
- Portable fire extinguishers include:
- Portable fire extinguishers – cabin and cockpit area
- Classes of fire include:
- Class A
- Class B
- Class C
- Class D
Pneumatic and Vacuum (11.16)
- Pneumatic and vacuum systems include:
- System layout and sources
- Pressure control
- Distribution
- Indications and warnings
- Interface with other systems
- System layout and sources include:
- Aircraft pressure and vacuum systems
- Venturi system vacuum supply
- Vacuum systems and pumps
- Low-pressure systems
- Vane-type air pump
- Combined vacuum and low-pressure systems
- Medium-pressure systems
- High-pressure systems
- Sources include:
- Engine bleed air supply
- APU supply
- Ground supply (external supply)
- Compressors
- Pressure control includes:
- Vacuum and low-pressure control
- Engine bleed air pressure control
- APU bleed air pressure control
- Distribution includes:
- Bleed air distribution
- Ducts
- High-pressure distribution system
- Emergency backup distribution systems
- Indications and warnings include:
- Sensors and indicators – example
- Typical pneumatic bleed air control panel
- Duct pressure indication
- Overheat detectors
- Interface with other systems includes:
- Introduction to interface with other systems### Engine Bleed Air System
- Low-Pressure (LP) bleed air is used at medium to high engine power settings during take-off, climb, and cruise conditions.
- High-Pressure (HP) bleed air is used at low engine rpm during descent when the low-pressure air supply is inadequate.
- The switch to HP air at low engine rpm ensures adequate pressure and flow to airframe systems during low-power engine operation.
- The changeover is automatic, and both bleed ports are never open at the same time.
- A Pressure Regulating and Shut Off Valve (PRSOV) is installed downstream of the LP and HP bleeds to prevent overpressure or overheat in the system.
Auxiliary Power Unit (APU)
- APUs are used to supply bleed air to all pneumatic systems when the engines are not running.
- A typical APU consists of a small turbine powerplant driving an electric generator.
- APUs are commonly used to supply bleed air on the ground only, but some APUs can supply bleed air in flight up to a specific altitude.
- The APU bleed air duct runs under the passenger floor to the air conditioning bay, where it joins the crossover duct on the pneumatic manifold.
- A check valve prevents reverse flow from engine bleed air into the APU.
Emergency Ram Air
- In case of failure of both packs, an emergency ram air inlet flap can be opened for A/C ventilation or smoke removal.
- The ram air selector switch must be set to "on" to open the emergency ram air inlet flap.
Electrically Driven Compressors
- Recent improvements in electrical technology enable the latest generation of jet transport aircraft to save fuel by minimizing the quantity of air bled from the engines.
- Electric motor driven cabin air compressors are used to pressurize the cabin and achieve the correct temperature and pressure.
- This technique avoids excessive energy extraction from engines and eliminates the need for pre-coolers, control valves, and pneumatic ducting.
Smaller Turbo-Prop Aircraft
- Smaller turboprop aircraft use a combination of engine bleed air and turbo compressors or jet pumps to pressurize the cabin.
- Turbo compressors are used to increase the amount of air taken into the cabin.
- Jet pumps use a venturi effect to induce a low pressure that draws in a larger mass of ram air.
Ground Supply Cart
- A ground cart may supply medium-pressure compressed air to the entire aircraft pneumatic system.
- The medium-pressure supply is not normally designed to cope with the demands of the air conditioning system.
- A low-pressure ground connector is connected to the ram air ducting for a low-pressure ground air conditioning supply.
Air Cycle System
- The air cycle system is used in larger passenger aircraft to supply ventilation and heated or cool air to the cabin.
- The system consists of an expansion turbine, air-to-air heat exchangers, and valves that control airflow through the system.
- The primary component of each pack assembly is the air cycle machine.
Air-Cycle System Operation
- The Flow Control Shut-Off Valve (FCSOV) controls the flow of hot bleed air to the primary heat exchanger and the hot side of the air mixing valve.
- The primary heat exchanger removes heat from the bleed air, which then goes to the compressor section of the air cycle machine.
- The compressor section increases the pressure and temperature of the partially cooled bleed air.
- The compressed air then goes through the secondary heat exchanger, where ram air removes some of the heat.
- The cold bleed air then goes into the water separator, where condensed moisture is removed.
- The cold bleed air is then mixed with hot bleed air in the mix chamber to regulate temperature throughout the cabin.
Air-Cycle System Components
- Flow Control Shut-Off Valve (FCSOV): controls the flow of air into the air conditioning pack.
- Primary and Secondary Heat Exchangers: air-to-air plate fin cross-flow-type heat exchangers that cool the bleed air.
- Air Cycle Machine: consists of a compressor section, turbine section, and water separator.
- Temperature Control Valve: mixes hot or cold air to regulate temperature throughout the cabin.
- Standby Temperature Control Valve: provides backup control for the discharge temperature of the air conditioning pack if the normal temperature control system fails.
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