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Questions and Answers
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?
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?
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What is the basic objective for Level 1 knowledge?
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Describe the objectives for Level 2 knowledge.
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What does Level 3 knowledge entail?
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Which aircraft systems use pneumatic power?
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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?
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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.
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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?
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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.
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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.
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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.
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What type of unit is the cabin sensor?
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Where is the temperature controller normally located?
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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.
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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?
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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.
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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?
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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.
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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.
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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?
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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.
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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:
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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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