Inert Gas System A321


IGGS :Inert Gas Generation System

CSAS: Conditioned Service Air System

FTIS : Fuel tank inert System

CCU : CSAS Control Unit

ICU : IGGS Control Unit

The Fuel Tank Inerting System (FTIS) is a Flammability Reduction Means to decrease Fleet Flammability Exposure to satisfactory levels. The FTIS gives protection to decrease the risk of fire and explosion in the center wing-box fuel tank (fuel tank). To get this protection, the FTIS causes inert conditions in the ullage space of the fuel tank

The FTIS has two sub-systems, the Inert Gas Generation System (IGGS) and the Conditioned Service Air System (CSAS). The CSAS gives the IGGS a conditioned air stream of the correct temperature, pressure and flow. The IGGS removes oxygen from the air stream, and makes Nitrogen Enriched Air (NEA) and Oxygen Enriched Air (OEA). The IGGS discards the OEA overboard, and puts the NEA into the ullage space of the fuel tank . The NEA goes into the fuel tank through a piping network, and it pushes the air with oxygen through the vent line, out of the fuel tank. This causes the inert conditions in the fuel tank.

An IGGS Controller Unit gives system control and health monitoring / Built-In Test Equipment (BITE).The non-pressurized belly fairing compartment holds the IGGS pallet. The pressurized avionics bay holds the IGGS Controller Unit. The pressurized fuel tank upper skin holds the distribution pipe and a dual-flapper check valve.

System Description :

After the air stream comes out of the CSAS, it goes into the IGGS Pallet . The IGGS Pallet contains an Isolation Valve (also referred to as Gate Valve); a Double-Ultra Low Particle Air Filter ; Temperature, Pressure and Oxygen sensors; an Air Separation Module (ASM), a Dual Flow Shut-Off Valve (DFSOV), a drain plug, ducts, clamps and brackets, and bonding straps. The air stream goes through the Isolation Valve into the Double-Ultra Low Particle Air (D-ULPA) Filter . The D-ULPA Filter cleans the air stream, to make sure that only clean air goes into the Air Separation Module. The Air Separation Module divide the air into OEA and NEA streams. The OEA goes out of the Air Separation Module to the atmosphere, and the NEA goes through the Dual Flow Shut-Off Valve out of the IGGS Pallet into the fuel tank. The duct that goes into the Isolation Valve, the D-ULPA Filter, and the duct between the D-ULPA Filter and the Air Separation Module inlet have a thermal insulation, to help make sure that the temperature of the air stream that goes into the Air Separation Module is more than 54 deg.C.

 The Isolation Valve closes if the air stream has a pressure of less than 15 psi (1.0342 bar), and/or its temperature is hotter than 85 deg.C (185.00 deg.F). The isolation valve has a mechanical visual position indicator for troubleshooting, and a closed-position indication switch, so the IGGS Controller Unit can monitor the isolation valve operation and help fault detection.

 The Dual Flow Shut-Off Valve controls the NEA flow to the fuel tank, sets NEA flow between low/mid/high and isolates the IGGS from the fuel tank. A drain plug for trouble shooting procedures.

The IGGS Controller Unit communicates with the CSAS Controller Unit (CCU) and the Air Data/Inertial Reference Unit 1 (ADIRU1) with the Aeronautical Radio Incorporated (ARINC) 429 protocol, and gives automatic system control and health monitoring / BITE. The IGGS Controller Unit receives data from the Isolation Valve, the Temperature Sensor, the Pressure Sensor, the Oxygen Sensor and the Dual Flow Shut-Off Valve. The CCU has interface with the IGGS Controller Unit, and the two operate independently to do the safety functions.

The filter has a thermal insulation, to make sure that the temperature of the air stream that goes into the Air Separation Module is more than 54 deg.C (129.20 deg.F) ( more than 34 deg.C with NEO A321 ).

The DFSOV closes if:

-the pressure of the NEA flow is less than 15 psi (1.0342 bar),and/or

-the NEA flow temperature is hotter than 85 deg.C (185.00 deg.F).

The IGGS Controller Unit gives a 28 VDC supply to the two solenoids of the DFSOV. With these two solenoids the IGGS Controller Unit controls the DFSOV to the open position, and the NEA flow between low/mid/high.

When the aircraft is on ground the FTIS does not operate, unless it is necessary for maintenance operations. During maintenance operations, there are two interactive BITE modes:

Interactive BITE without bleed air, and

Interactive BITE with bleed air from Auxiliary Power Unit (APU) or ground supply, air-conditioning Pack1 ON and Pack2 OFF.

During aircraft flight, the FTIS operates automatically when the ICU receives a GO signal from the CSAS. The aircraft crew does not operate the FTIS, because it has automatic control.

The FTIS has three NEA flow modes:

-Low, during climb and cruise phases;

-Mid, during approach phase;

-High, during usual descent phase.

If the ASM does not operate correctly again and again three times, the ICU sends a failure message to the CCU, and the CCU gives an Electronic Centralized Aircraft Monitoring (ECAM) warning to the Centralized Fault Display Interface Unit (CFDIU), at the end of the flight, for maintenance functions.

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