Fuel Tank Inerting System (FTIS)

• Fuel Tank Inerting System (FTIS) consists of two sub-systems: Conditioned Service Air System (CSAS) and Inert Gas Generation System (IGGS).

Conditioned Service Air System (CSAS)

• The system gets hot air from the Engine bleed air system
• The system decreases the temperature of the hot air to a level compatible with the IGGS sub-system.
• The components of the system are:
  • Conditioned service air system Controller Unit (CCU)
  • CSAS isolation valve
  • and a heat exchanger

Controller Unit (CCU)

• The CCU is responsible for system control and health monitoring using Built-In Test Equipment (BITE)
• The CCU also has interfaces with the Flight Warning System (FWS) and Centralized Fault Display System (CFDS).
• The isolation valve protects the system from:
  • Low pressure
  • Overpressure
  • Overtemperature
• The heat exchanger reduces the air temperature from the engine bleed.
• Engine 1 acts as the primary bleed source, while Engine 2 acts as the secondary source via the X Bleed valve.
• Alternatively, the APU or a Ground Cart supply can facilitate interactive ground testing.
• The CSAS receives bleed air from the Engine Bleed Air System, conditioning it for the IGGS.
• Initially, an ozone converter reduces ozone levels in the bleed air, protecting IGGS components.
• Subsequently, the CSAS heat exchanger lowers the air temperature to 60°C with a tolerance of +/-6°C.
• The bypass valve is situated in the heat exchanger bypass duct and is regulated by the CSAS.
• This valve introduces hot air downstream of the heat exchanger to maintain temperature within set limits.
• A dual-element temperature sensor and a pressure sensor placed on the output duct monitor temperature and pressure before air enters the IGGS.
• The CSAS isolation valve shuts to halt the system in the event of overpressure or overtemperature incidents.
• The system is positioned on the left side of the aircraft's belly fairing.
• Bleed air enters from the High-Pressure Ground Connector (HPGC) tube.
• The CSAS isolation valve remains open during normal operation, allowing air to proceed through the ozone converter.
• Air temperature decreases post ozone conversion via the CSAS heat exchanger, with output channeling to the IGGS.
• The controller sits in the FWD electronics rack (90VU) within the avionics compartment.
• The controller manages the system, monitors health via BITE, and interacts with both the FWS and the maintenance computer.
• Any malfunction triggers the "INERT FAULT" status message during flight phases 1 and 10 for maintenance alerts.
• The MEL permits aircraft dispatch with the system inoperative for ten days, needing no specific maintenance steps.
• The Controller links with the Air Conditioning System Controller (ACSC) and Engine Interface Units (EIUs) to ensure constant bleed pressure during descent.

Inert Gas Generation System (IGGS)

• The system uses an Air Separation Module (ASM) to extract oxygen from the conditioned air stream.
• It separates Nitrogen Enriched Air (NEA) from Oxygen Enriched Air (OEA).
• The OEA is vented overboard.
• The Dual Flow Shut Off Valve (DFSOV) governs NEA flow into the center fuel tank.
• The DFSOV enables switching between low, middle, and high NEA flow rates. It also isolates the IGGS from the center fuel tank.
• The IGGS controller manages the system and monitors health using BITE.
• The isolation valve is a spring-loaded solenoid valve and is normally closed
• The IGGS Controller Unit (ICU) commands the valve to open, allowing conditioned air to enter from the CSAS when operational.
• It closes if the air from the heat exchanger is too low in pressure or too hot.
• FTIS provides NEA, a low-oxygen gas that poses an asphyxiation risk if confined.
• The IGGS includes:
  • An IGGS Isolation Gate Valve
  • A D-ULPA filter
  • A temperature sensor
  • Two pressure transmitters
  • An oxygen sensor
  • An Air Separation Module (ASM)
  • A Dual Flow Shut Off Valve (DFSOV)
  • A dual flapper check valve and
  • An IGGS Controller Unit (ICU)
• Downstream of the D-ULPA filter, temperature and pressure sensors communicate air data to the ICU.
• The ASM is the core, it extracts oxygen and sends NEA into the center fuel tank, with OEA exiting through an outlet on the HPGC door.
• Oxygen levels are monitored by a sensor downstream of the ASM, preventing high concentrations in the center fuel tank.
• The oxygen sensor also has a pressure sensing capability that is energized and thus prevents over-pressure from occurring in the center fuel tank
• The DFSOV manages NEA flow, adjusting between low, mid, and high settings relative to flight phases and isolates the IGGS upon abnormal operation.
• A dual flapper check valve acts as a secondary measure against fuel back-flow.
• Should overpressure or overtemperature occur, the ICU cuts power to the IGGS Isolation Gate Valve solenoid, closing the valve.
• An oxygen sensor detects an oxygen rate exceeding 12%, prompting the ICU to cut power to both the IGGS Isolation Gate Valve and DFSOV solenoids.
• The ASM sits at the heart of the Inert Gas Generation System, extracting oxygen from compressed air.
• It produces NEA and OEA, directing NEA to the center fuel tank and OEA overboard.
• Structurally, the ASM features a semi-permeable hollow-fiber membrane bundle within a pressure containment canister.
• Under standard conditions, the DFSOV stays shut, isolating the IGGS from the fuel tank.
• The ICU uses two solenoids to manage DFSOV position (OPEN/CLOSE) and modulate NEA flow (LOW/MI/HIGH).
• NEA goes from the IGGS to the center fuel tank using a pipe and nozzle arrangement.
• A dual check valve setup stops fuel from the fuel tank getting into the IGGS.
• The system, housed in single unit, features two in-line flapper check valves.
• The valves can be found on the outside of the center fuel tank.

ICU Interfaces

• ADIRU 1 feeds signals regarding Standard Altitude:
  • True Airspeed
  • Total Air Temperature
  • Altitude Rate to the ICU
• The CCU facilitates communication among the IGGS controller, CFDIU, and FWS.
• This inter-controller communication provides system status.
• If the CSAS shuts down because of overtemperature, the CCU informs the ICU, which compares sensor readings between systems.