ATR 600 Series Air Leak Detection System Quiz

Pneumatic System

• The pneumatic system supplies pressurized air to various aircraft systems, including air conditioning, ventilation, pressurization, and de-icing.
• Compressed air is bled from the engine compressors at the LP or HP stages.

General Description

• The pneumatic system has two separate bleed duct subsystems, one for the left and one for the right engine.
• Each subsystem is fed by the corresponding LP and HP engine compressors.
• The system includes ducting, various valves, sensing elements, and pressure regulators to maintain controlled pressure and temperature.

Cockpit Panels

• Cockpit panels for the ATR 500 series are located on the overhead panel.

Interfaces

• The pneumatic system has interfaces with other systems, including air conditioning, ventilation, pressurization, and de-icing.

Features

• The system has a "Hotel Mode" which is used on the ground to provide electrical supply and air conditioning.
• In Hotel Mode, the LP and HP stages run, and the propeller brake is locked.

Cross Feed

• The crossfeed valve is installed on the crossfeed duct and connects the LH and RH air bleed ducts.
• The valve is open on the ground only when one engine is running or the propeller brake is engaged.

Magnetic Indicators

• Magnetic indicators are fitted on the ATR 500 series to indicate HP valve failures.

Engine 2 Oil Cooling

• When engine 2 operates in Hotel Mode, two air ventures enable the activation of air flow through the oil cooler.

Safety Precautions

• Pneumatic safety precautions must be taken during maintenance.

Distribution

• The pneumatic distribution system directs and controls the distribution of pressurized air to various systems, including air conditioning and ice protection.

Engine Bleed Air Supply System

• The engine bleed air supply system consists of two separate bleed duct subsystems, one for the left and one for the right engine.
• The system includes ducting, various valves, sensing elements, and pressure regulators to maintain controlled pressure and temperature.
• The ducts from the LP and HP ports join inside the engine nacelle to form a single duct.
• The duct passes from the engine nacelle through the centre wing leading edge, the interspace between the fuselage external skin and internal lining, to the front undercarriage area.

Valve Descriptions

• HP bleed air valve description: The valve opens at low power engine ranges and regulates air pressure at 25 psi in flight and 38 psi on ground.
• LP check valve description: The valve prevents reverse flow towards the LP compressor when the HP bleed valve is opened.
• Bleed air shut-off valve description: The valve controls bleed airflow for the air conditioning and prevents overpressure on the ducts.
• Overpressure switch description: The switch is installed upstream the bleed air shut-off valve to avoid overpressure on the ducts.
• Thermal switches description: The switches are installed downstream the bleed air shut-off valve to avoid overtemperature on the ducts.
• Crossfeed valve description: The valve is installed in the pressurized underfloor area and connects the LH and RH air bleed ducts.
• Bleed air check valve description: The valve prevents airflow towards the left engine compressor in Hotel Mode.

System Operations

• On the ground, the crossfeed valve is open only when one engine is running or the propeller brake is engaged.
• In flight, the crossfeed valve is closed.
• The system monitors duct air leaks up to the air conditioning pack valve.
• In case of air leak detection, an associated Leak light illuminates on the Air Bleed Panel.### Engine Bleed Air Supply System Description
• The engine bleed air supply system is supplied with LP port when PL angle is set > 37°.
• HP valves close when PL angle is set > 37°.
• When PL angle is set < 37° and pressure is < 25 psi, HP valves open and the system is regulated at 25 psi.

HP Bleed Air Valve Description

• The HP bleed air valve is fitted on the HP manifold located in the engine nacelle.
• The valve is normally closed and has a dual differential pressure regulator.
• HP valve low pressure reference is 25 psi, and high pressure reference is 38 psi.
• Valve position is monitored by micro-switches.

HP Bleed Air Thermal Resistance

• The thermal resistance sensor is located on the engine HP compressor stage.
• When the sensor detects a temperature > 270° C, the HP bleed valve is closed and the MFC bite loaded magnetic indicator turns yellow.

LP Bleed Air Check Valve Description

• The LP bleed air check valve is fitted in the LP manifold located in the engine nacelle.
• The valve has two semi-circular butterfly flaps held closed by a spring.
• The valve prevents reverse airflow into the engine LP compressor when the HP bleed is operating.

Bleed Air Shut Off Valve Description

• The bleed air shut-off valve is a spring-loaded, normally closed shut-off valve.
• The valve is pneumatically actuated and electrically controlled.
• The valve is closed during engine start until NH 45% + 30s.

Bleed Air Check Valve Description

• The bleed air check valve prevents reverse airflow to the left engine compressors when the right engine is operating in Hotel Mode.

Cross Feed Valve Description

• The cross feed valve is an electrically controlled, pneumatically actuated shut-off valve.
• The valve interconnects the right and left ducting to allow bleed air to flow from one system to the other.

Wing Leading Edge Ventilation System

• The wing leading edge ventilation system maintains a low temperature level inside the wing leading edges.
• The system obtains ventilation through a ram air intake scoop located in the top of the engine nacelle.
• The system allows fuel vapors to escape, preventing possible fire due to a hot air bleed duct leakage.

Deactivation of the Cross Feed Valve

• Fault symptom: On panel 22 VU, OVHT and LEAK lights are illuminated.
• Fault isolation: TASK ATR-A-36-11-XX-03004-421A-A.
• Deactivation procedure: Disconnect electrical connector, remove valve, and blank off electrical connector.

Bleed Air Overtemperature Switches Description

• The switches are hermetically sealed, stainless steel probes.
• They monitor the air bleed and close the bleed air shut-off valve and HP bleed valves in case of overtemperature.
• The operating range of the switches is 274 ± 6,7 °C (525 ± 12 F), and the reset temperature is 250 °C (482 F).

Bleed Air Pressure Switch Description

• The pressure switch is fitted on the bleed air duct, upstream the bleed air shut-off valve.
• The switch closes the bleed air shut-off valves when air bleed pressure > 80 psi.
• Fault light illuminates on the corresponding air bleed push button.

Air Leak Detection System Description

• The system is a continuous monitoring system installed to detect duct leakages by thermal wire sensing element.
• The system consists of two subsystems, one for each bleed system.
• The system is installed in the wing leading edge, wing to fuselage fairing, upper and lower fuselage floor, and air conditioning pack area.

Air Leak Detection System Operation

• When an element of the leak detection wire heats to the alarm temperature of 153 ± 8 °C, the air leak control unit sends a signal.
• The signal illuminates the corresponding LEAK legend and, after a one-second delay, the bleed air shut-off valve and HP valve close.

Control Unit Description

• The control unit is installed on shelf 92VU in the electronic rack.
• It is an electronic device with two monitoring circuits.
• The level circuit initiates an alarm when the impedance of the continuous element reaches a predetermined low level.

Sensing Elements Description

• The sensing elements are fitted closed to the pneumatic ducts.
• They consist of a solid nickel conductor embedded in an insulating material and encased in an inconel tube hermetically sealed at both ends.
• When an air leak occurs, the air is drawn to holes, located in front of the leak detection wire.

Fault Isolation

• Fault symptom: On panel 22VU, LEAK legend is illuminated.

• Fault isolation: TASK ATR-A-36-22-XX-02001-421A-A.

• Deactivation procedure: Remove and install the sensing elements as per Ref.MP ATR-A-36-22-20-00ZZZ-520Z-A and Ref.MP ATR-A-36-22-20-00ZZZ-720Z-A.### ATR 42-500/72-212A (PWC PW120) Pneumatic System

• The Air Bleed Panel is located on the Overhead Panel and displays various indicators and controls.

• The X VALVE OPEN light illuminates when the crossfeed valve is open, and is inhibited in flight.

• The X VALVE OPEN light also illuminates when the crossfeed valve is stuck open with both engines running or shut down.

• The OVHT light illuminates when the bleed duct temperature exceeds 274°C (525°F), and auto-closes the bleed valves.

• The LEAK light illuminates when the loop temperature exceeds 153°C, and auto-closes the bleed valves with a one-second delay.

Air Bleed Panel Indicators

• Engine 1 (2) Bleed Push button controls both bleed air shut-off and HP bleed valves.
• The FAULT light illuminates in case of bleed valve position disagreement with the relevant push button.
• The OFF light illuminates when the push button is released, and the HP and bleed valves are closed.

Pneumatic System Indications on ATR 600 Series

• Pneumatic system indications are displayed on the Air Bleed Panel and the SD Cabin page of the Multi-Function Displays.
• The "FAULT" amber light illuminates in case of bleed air shut-off valve position disagreement.
• The "ON" light illuminates when the push button is depressed, and the bleed air shut-off valve is open.
• The "OFF" light illuminates when the push button is released, and the HP and bleed valves are closed.

Bleed Air System Symbols on ATR 600 Series

• The symbols are used to indicate the state of the bleed air system.
• State 1: Engine 1 (2) bleed air pushbutton is released, and both engines are running.
• State 2: Engine 1 (2) bleed air pushbutton is depressed, and both engines are running.
• State 3: Engine 1 (2) bleed air pushbutton is released, and one engine is running.
• State 4: Engine 1 (2) bleed air pushbutton is depressed, and one engine is running.

Controls and Indicators on ATR 600 Series

• The ENG 1 (2) BLEED air pushbutton controls both bleed air shut-off and HP bleed valves.
• The "ON" light illuminates when the push button is depressed, and the bleed air shut-off valve is open.
• The "OFF" light illuminates when the push button is released, and the HP and bleed valves are closed.

Maintenance Practices

• The Air Leak Detection System Operational Test/Check is performed by pressing the Air Bleed Leak PTT push button switch.
• The test checks the continuity of the loops, the controller, and the associated warnings.
• The Air Leak Detection System Check is performed by pressing the Air Bleed Leak PTT push button and checking the Leak amber lights.
• The check sequence includes: LH or RH wing leading edges, LH or RH wing to fuselage fairings, LH or RH fuselage sidewalls, fuselage underfloor, and LH or RH conditioning pack area.

This quiz covers the Air Leak Detection System of the ATR 600 Series aircraft, including the location of the HP Bleed Valve position, the air leak momentary switch, and troubleshooting operations.