Airbus FAST Magazine 44 p8 p16

FUEL TANK INERTING SYSTEM - A RETROFIT INDUSTRIAL CHALLENGEFA

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Alain LEROUXHead of Multi-Programme

and Business ConsolidationAirbus Customer Services

Sammy BOUGACIFuel Systems Engineer

Airbus Customer Services

Laurent SEGUYFuel Systems EngineerAirbus Customer Services

Fuel TankInerting System

also calledFlammability Reduction System (FRS)

A retrofit industrial challenge for the next decade

This article seeks to describe the flammabi-lity reduction subject in more details, whilst

clarifying the technical, industrial and retrofitstandpoints.

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FUEL TANK INERTING SYSTEM - A RETROFIT INDUSTRIAL CHALLENGE

BackgroundAs a result of a major accidentresulting from a fuel tank explosion,in 1996 the Federal AviationAuthority (FAA) Technical Centreundertook researches into fuel tankflammability and ignition risks.Since 2000, Airbus has activelybeen involved in flammabilityreduction, conducting studies forthe FAA and flight tests on theA320 prototype in 2003.

As a result of these researches,the FAA has developed a rulethat requires operators and manu-facturers of air transportationcategories to take actions that willreduce the exposure to catastrophicfuel tank explosion.

This can be achieved by mitigatingthe two main conditions that mustbe present in a fuel tank to supportcombustion that can lead to a fueltank explosion:• An ignition source,• A flammable fuel-air gaseousmixture.

The prevention of ignition iscovered by the FAA (SFAR 88) andEASA (INT- Policy 25/12) require-ments for which Airbus demons-trated the full means of compliancein May 2006.

As well as aircraft and equipmentmodifications, these requirementshave also been introduced in thenew Critical Design ConfigurationControl Limitations (CDCCLs).The process has been set up toreduce the potential ignitionsources within the fuel tanks (i.e.pumps, wirings...) whereas theFuel Tank Inerting System (FTIS)is a means to reduce theflammability of the fuel tanks.So both are complementary andcannot supersede each other.

Fuel Tank InertingSystemSTATUS ON THE REGULATIONS

The FAA and EASA have deve-loped requirements for designprecautions to mitigate the risksassociated to fuel tank flammability.

FAA

On 21 July 2008, FAA requiredoperators and manufacturersto incorporate a FlammabilityReduction Means (FRM) or Igni-tion Mitigation Means (IMM)on fuel tanks having a flammabi-lity exposure exceeding certainthresholds, following the officialpublished FAR 25, 26, 121, 125and 129 amendments.

These amendments affect newaircraft type certification, newaircraft in production and in-service aircraft produced after1 January 1992 (see informationbox on the following page).

Fuel vapour

Flammabilityreduction

SFAR88Int policy 25/12

Ignition source Oxygen

Prevention of ignitionand reduction of flammability


EASA

For new aircraft, EASA (EuropeanAviation Safety Agency) haveissued for consultation a draftamendment to CS-25 (NPA 2008-19) which is harmonized with thecorresponding American standard(FAR 25). A final decision isexpected by the 2nd quarter of 2009.

For in-production and in-serviceaircraft, EASA have stated theywill publish in 2009 a NPA to CS–26 and a Safety Directive to beadopted by the 4th quarter of 2010after taking into account thereceived comments.

AIRBUS COMPLIANCE TO THE RULES

Airbus demonstrated that ‘onlythe centre tank’ of some of itsexisting aircraft has fleet averageflammability exposure exceeding7% and is affected by therequirements of the FAR Part 26.There is no necessity to do anymodification on other tanks.It concerns the following aircraft:• A320 Family,• A330-200, A340-200,A340-300, A340-500, A340-600,

• A300-600.

At the date of publishing, the rulesapply only for passenger aircraftproduced and delivered after1 January 1992 flying with USoperators or N-registered passengeraircraft.

SYSTEM DESCRIPTION

The Airbus solution for the A320Family and A330/A340 Family isbased on a system developed withthe supplier, Parker, which reducesthe oxygen levels of the centre tankullage space.

The installation of this new deviceis designed to avoid themodification of existing systemsand structures. The Fuel TankInerting System (FTIS) interfaceswith the following systems:• Fuel systems,• Environmental Control Systems,• Engine bleed air supply systems.

Several other alternate means havebeen studied (e.g. reduction of heatsources, tank pressurisation andfoam). But they lead either toimportant structure modificationsor operational constraints.

One solution studied was to usebottled nitrogen, but it was dis-missed due to the significantrequired additional airport infras-tructure and the impact on aircraftTurn Around Time (TAT).

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n o t e s

• Existing freighter aircraft orpassenger to freighter convertedaircraft are not involved.

• For the A300-600 aircraft,no more N-registeredpassenger aircraft will beoperated at the time of the FAAdeadlines for the retrofitcompletion. If the FlammabilityReduction Means (FRM)is required by any localAirworthiness Authoritiesas the fleet averageflammability exposure near 7%,a modification basedon a cooling concept of thecentre tank will be proposed.

i n f o r m a t i o n

• FAR Part 25: Amendment 125It will be the certification basisfor new aircraft types. It updates§ 25.981 by including the flammabilitycriteria and means to be met by thetanks, the IMM requirements, theinstruction for ContinuedAirworthiness. It defines themethodology to be used to performthe fuel tank flammability analysis,

• FAR Part 26: Amendment 3This amendment is applicableto existing Type Certificates (TC)including Supplemental TypeCertificates (STC). It requiresfor passenger aircraft of 30or more seats manufacturedon/or after January 1st, 1992:- to submit to FAA by Feb 16th, 2009.

A flammability analysis for eachtank as per FAR Part 25 appendix N,

- to provide a FRM or IMM for tankshaving a fleet average flammabilityexposure exceeding 7%,

- to submit the required FRM/IMMchanges and associated ServiceInstructions for approvalby Dec 26th 2010,

• FAR Part 121: Amendment 340It applies to US operators whateverthe country of registrationof the aircraft used by theseoperators. It sets requirementsfor retrofit of passenger aircraftwith a Flammability Reduction Means(FRM) or an Ignition Mitigation Means(IMM) if required per FAR Part 26.The retrofit shall be completedat the latest by December 2017with an intermediate requirementto retrofit half of the operator fleetby December 2014. New aircraftdelivered to an operator afterDecember 26th, 2010 must be fittedwith an operational FRM or IMM,

• FAR Part 125: Amendment 55Similar requirements to those of FARPart 121 applied for specific typeof commercial passenger carryingoperations,

• FAR Part 129: Amendment 46Similar requirements to thoseof FAR Part 121 applied for foreignoperators of aircraft registeredin the United States.

FAA ruling requirements (summary)

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SYSTEM INSTALLATIONON AIRCRAFT

The system is installed in the left handside of the aircraft belly fairing asshown in figure 1.

PRINCIPLE

The system (see figure 2) providesprotection against fuel tank fire andexplosion by creating an inertcondition within the ullage space of thefuel tanks. This is achieved by usingoxygen depleted air known as NitrogenEnriched Air (NEA) to displace theoxygen in the tank ullage spaces.

The system is based on a continuousflow principle and produces NEA fromconditioned engine bleed air by gasseparation, then injects it into the tank.


Air Separation Module(ASM)

Inlet flowConditioned Service Air System

(CSAS)

Oxygen Enriched Air(OEA)

Fuel tank flowNitrogen Enriched Air

(NEA)

Figure 2

Air Separation Module flow

Installation of the FTIS (Fuel Tank Inerting System)in the left hand side of the belly fairing

Figure 1

n o t e s

Ullage is the space within a fueltank above the liquid propellant.


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TECHNICAL DESCRIPTION

The architecture (see figure 3) isbroken down in two major sub-systems:

1) The Conditioned Service AirSystem (CSAS)

2) The Inert Gas GenerationSystem (IGGS)

THE CSAS

Some bleed air is taken from thepneumatic air distribution systemand then cooled down to a levelcompatible with the IGGS sub-system using the air from theexiting ECS (Environmental Con-trol System) ram air channel.It is organized into two functionalelements: a temperature controlsubsystem and the CSAS IsolationValve with an ozone convertersubsystem. Driven by the CSAScontroller, the solenoid ControlledIsolation Valve ensures theshutdown of the system if theengine bleed air pressure isabnormally low or if over-pressureor over-temperature is detected

from the sensors. The ozone con-verter reduces the amount of ozonein the bleed air to protect the IGGScomponents.

The CSAS controller, located inthe avionics’ bay, performs thesystem control and health moni-toring BITE (Built In TestEquipment) and is interfaced withthe Flight Warning System (FWS)and maintenance computer.

THE IGGS

It uses Air Separation Modules(ASM) to filter the conditioned airstream, creating Nitrogen EnrichedAir (NEA) and Oxygen EnrichedAir (OEA) (see figure 4); the OEAis sent overboard.

The air at the ASM inlet remainsclean, free of hydrocarbons, dustand other contaminants thanksto the HEPA (High EfficiencyParticle Air) filter. Being connec-ted to the fuel tank, the systemmust meet very stringent safetyrequirements:

Isolation valve

Ozone converter

ASM

OxygenEnriched Air

C35

A320: Installation of the Isolation valve and Ozone converter A320: Nitrogen Enriched Airgoing into the centre tank

C36

C35Flightdirection

NitrogenEnriched Air

ProductO2 RichWaste

O2 CO2H2O

Air

NEA

13


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Twin check valve

Centretank

Dual Flow ShutOff Valve

Pallet

O2sensor

Air separationmodule

Waste flow(O2 rich)Overboard exit

Heatexchanger TCM

Tempcontrolvalve

HEPAfilter

SensorsSensors

IGGS controllerCSAS controllerFWCCFDIU/CMC

Bleed line

Isolationvalve

O3 converter

Figure 3

It is the core of the Inert Gas GenerationSystem. The objective is to reducethe centre wing tank ullage O2concentration to below 12%during most conditions. Each ASMis a semi-permeable hollow fibre

membrane bundle contained in a pressurecontainment canister. This canisteris a cylinder with three ports. There isonly one ASM on the A320 Family aircraft,two on the A330-200 and A340-200/300,and three on the A340-500/600.

• Air greater than 200° Cmust not come into contactwith fuel or fuel vapour,

• Fuel tanks must not beover-pressurized,

• Prevention means for fuelingress upstream to the ASM.

Sensors, valves and controllersensure these safety requirements.Downstream of the ASM is anoxygen sensor ensuring that theoxygen concentration is below12%.

A Dual Flow Shut Off Valve is thenused to control the NEA flow to thefuel tank and enables the system toswitch between low/mid/high NEAflows, and to isolate the IGGSfrom the fuel tank.NEA is distributed from the IGGSto the fuel tank through a twincheck valve which provides adouble barrier to the potentialback-flow of fuel.The IGGS controller provides sys-tem control and health monitoring/BITE.

FTISsimplified schematic

Figure 4

Air Separation Module(ASM) description

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FTIS operationThe Fuel Tank Inerting System(FTIS) operates during flight whenthe bleed air is supplied. The systemdoes not operate when the aircraft ison the ground, except duringmaintenance operations.

It has three flow modes designed toachieve the flammability reductionobjective during the different flightphases:• Low is used in climband cruise,

• Medium is used in approachand slow descent,

• High is used in descent.

The FTIS will not be operationalwhen either the electrical power orthe bleed are unavailable, nor whenthe anti-ice is ON with a non-operating engine (i.e. A330).

OPERATIONAL IMPACTS

The FTIS has automatic controlwith no requirement for crewintervention.

Any system fault leading to the lossof inerting capability generates acockpit and maintenance messageat the end of the flight (flight phase10) for maintenance purposes:• For A320 Family a maintenanceSTATUS: ‘INERT FAULT’,

• For A330/A340 Familyan ECAM message: ‘FUELINERTING SYS FAULT’.

The aircraft can be dispatched underMinimum Equipment List (MEL)with the system inoperative during10 days with no specific maintenanceaction.

The implementation of these newcockpit and fault messages requiresupgraded standards of the FlightWarning Computers (FWC) andmaintenance computers (CFDIUfor the A320 Family, CMC forthe A330/A340 Family) (seeinformation note).

MAINTENANCE IMPACTS

In order to ease the maintenance,the heat exchanger with the HotAir Bypass Valve, the Temperatureand pressure sensors of the CSASsubsystem are installed in theTemperature Control Module (TCM)(see figure 5).


ECS Air Conditioning Pack

ECSMain HeatExchanger

Hot Air Bypass Valve

CSAS Heat Exchanger

CSASTemp Control Module

(TCM)Ram AirFlow

No action required

for pilots


Alarm and maintenancecomputersIn order to provide alarmand maintenance messages,the prerequisites are:• The Flight Warning Computer

(FWC) standard must be:- H2F5 for the A320 Family- T3 for the A340-500/600- L11 for the A340-200/300

and A330-200• The maintenance computer

must be at:- Standard 10 for the CFDIU

(A320 Family)- Standard L8-A for the CMCs

(A330/A340 Family)

Figure 5

Temperature Controle Module

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Airbus has taken the same approachfor the design of the IGGS.A pallet is used to group the majorIGGS components.They are as seen in figure 6:• The Gate Valve,• The HEPA filter,• The Pressure sensor,• The Temperature sensor,• The ASM (s),• The Oxygen sensor,• The Dual Flow Shut Off Valveand ducting.

In order to maintain the systemperformance and to minimize theexposure to unscheduled main-tenance, some scheduled main-tenance actions are required asdescribed in table 1.

The industrialchallengeof the retrofitcampaignThe FAA rules impacts around 900Airbus aircraft in-service to beretrofitted within seven years.If EASA follows the FAA decisionon retrofit, around 4500 Airbusaircraft will have to be retrofittedduring the next decade.

PLANNING

Under such a hypothesis, a strongcoordination with every operator isa must. A well-prepared retrofitand embodiment planning has tobe set up between the operators andAirbus to avoid any industrialbottlenecks.

Tie rod attachments(MS14103 Spherical Brg.)

O2 sensor

ASM

NEA outlet

filter

Nameplate

OEA outlet

Aft palletbracket

Air inlet

Gate valve

Pressure sensor

Temperature sensor

Dual Flow Shut Off Valve

1 No special tools or test equipment required for scheduled maintenance tasks2 Drain cap is opened to check for liquid fuel ingress following no operationMMEL periods or after a fuel tank overfill

3 Valve Leak test is performed at the liquid drain plug locationand the test port location between the check valves

Task Task time (hours) Check labor time (hours) Interval Procedure 1 2

0.75 1.2 27,000 Removehours and replace,

leak test

0.28 0.45 7000 Removehours and replace,

leak test

0.58 0.75 6000 Removehours and replace

Consistent with ECS heat exchanger cleaning interval

1.0 1.5 12,000 Testhours and replace

as needed

ReplaceASM

Replacefilter element

OzoneConvertercleaning

HeatExchangercleaning

Check valveand DFSOVLeak test 3

Table 1

IGGS Pallet

Figure 6


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AIRBUS RETROFIT OFFER

Airbus Upgrade Services throughthe RFC/RMO process will provi-de customized commercial andtechnical services consisting of aretrofit package with:• Two Service Bulletins:

- One SBfor the structuraland electrical provisions,

- One SBfor the equipment installationallowing the customerto complete the retrofitin packages during C-checks,

• Airbus kits (brackets, pipes,rods, wiring, etc.),

• Specific FTIS equipmentfrom Parker and Liebherr,

• The coordination of the kitand equipment deliveries.

Flight Warning Computers andmaintenance computers’ standardsshould accept messages provided bythe FTIS (see information for therequested corresponding standards).Upon request, technical support onsite can be provided. Airbus willalso provide relevant trainingcourses to your maintenance staff.

EMBODIMENT ON AIRCRAFT

About 500 man-hours are neededwith a lead-time of 7/8 days ifdone in one operation (provisionsand installation). This takes intoaccount the aircraft preparation(scaffolding, centre tank ventingand all the tests). The work can bedone in two packages (provi-sions, then equipment installation)allowing the operator to performthe modification within twoC-checks.

g l o s s a r y

ASM: Air Separation ModuleBITE: Built In Test EquipmentCFDIU: Centralised Fault DisplayInterface UnitCMC: Centralised MaintenanceComputerCSAS: Conditioned Service AirSystemDFSOV: Dual Flow Shut Off ValveEASA: European Aviation SafetyAgencyECS: Environmental Control SystemFAA: Federal AviationAdministrationFAR: Federal Aviation RegulationsFRM: Flammability reduction MeanFTIS: Fuel Tank Inerting SystemFWC: Flight Warning ComputerHEPA: High Efficiency Particle AirIGGS: Inert Gas Generation SystemIMM: Ignition Mitigation MeanMEL: Minimum Equipment ListNEA: Nitrogen Enriched AirNPA: Notice for ProposedAmendmentOEA: Oxygen Enriched AirRFC/RMO: Request For Change/Retrofit Modification OfferSTC: Supplemental type CertificateTC: Type Certificate


Airbus documentation• SFAR 88: S.I.L. 28-072

Fuel tank protection againstignition source,

• FTIS: OIT 999.0007/06ATA28-FAA NPRM on flammabilityreduction system retrofit,

• FTIS: OIT 999.0084/08ATA47-FAA flammability,reduction system introduction

• AirbusWorld portal: dedicatedpage ‘Comply with Fuel TankSafety’.

To comply with the FAA flammabilityreduction rules, Airbus have developedthe most cost effective technicalcompromise in terms of maintenanceand operations. Airbus is fully committedin supporting the operators with thesenew requirements taking into account

the deadlines set up by the authorities.This can only be achievedwith the cooperation of the concernedoperators that will overcome thischallenging embodiment of the Fuel TankInerting System technology by schedulingthe installation in due time.

Conclusion

CONTACT DETAILS

RFC/RMO [email protected]

Technical queriesRonan ALLARDDesign ManagerUpgrade ServicesAirbus Customer ServicesTel: +33 (0)5 62 11 07 73Fax: +33 (0)5 62 11 08 [email protected]

Documents

Airbus FAST Magazine 44 p8 p16