1. Development and Testing of the FAA Simplified Fuel Tank Inerting System
William Cavage & Robert Morrison AAR-440 Fire Safety Branch Wm. J. Hughes Technical Center Federal Aviation Administration
International Fire and Cabin Safety Research Conference Parque das Nações Conference Center Lisbon, Portugal November 15-18, 2004

2. Outline Background System Architecture Test articles Results Summary
Inerting theory
Inerting History
ASM theory of Operation
System Architecture
Test articles
Boeing 747SP Ground Test Article
Airbus A320 Flight Test Aircraft
NASA 747 SCA
Results
Initial Ground Testing
Single ASM Flight Test Data
Complete System Flight Test Data
Summary
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3. Background
Fuel tank explosion accident history highlighted by TWA800 disaster
Past Certification of fuel systems based on ignition source elimination, not flammability control/reduction
FAA Certification Office has been seeking flammability elimination/reduction rule since 1997
Multiple industry rule making advisory working groups (ARAC HWGs) yielded no solutions palatable to FAA and industry
Previous research illustrated potentially most efficient fuel tank inerting method is OBIGGS
Needed to do detail study of onboard inert gas generation systems (OBIGGS) specifically for commercial applications
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4. Inerting Background
Inerting refers to rendering the ullage (air above fuel) unable to propagate a reaction given flammable conditions and ignition source
In this case Refers specifically to reducing tank oxygen concentration
Other methods of compliance possible
Fire Triangle must be satisfied to have a reaction (explosion) in the ullage of a fuel tank
Ignition Source
Correct ratio of fuel and air
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5. Fuel Tank Inerting History
Inerting has been studied since 1950s
Stored gas inerting used by military in 1970s
FAA built and tested demo cryogenic nitrogen system on DC-9
DOD did OBIGGS research using PSA and ASMs
Found HFM technology made ASMs very cost effective for OBIGGS
FAA research illustrated fuel tank inerting could be practical if applied in a cost effective manner
Initially focused on ASM performance for fire suppression capabilities
After second ARAC, focused on using ASMs to generate inert gas on an aircraft from bleed air during the flight cycle
FAA experiments agree with previous experiments and indicated that a tank oxygen concentration below 12% will render tank inert
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6. Hollow Fiber Membrane
Hollow fiber membrane technology uses the selective permeation properties of certain materials to separate air into two streams, one nitrogen rich and the other oxygen rich (compared to air).
Materials are woven into hair-sized fibers and bundled by the thousands into a canister called an air separation module (ASM)
Pressurized air is forced through the membrane fibers, allowing fast gases to escape through the membrane wall and the nitrogen rich stream to pass through
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7. System Architecture
A simplified inerting system conceived by Ivor Thomas (CSTA for Fuel Systems) illustrated feasibility
Concept utilizes HFMs in a two flow methodology
Uses low flow mode during taxi, takeoff, ascent, and cruise to deplete CWT of oxygen almost completely
Uses high flow mode during descent to offset (but not eliminate) the air entering the fuel tank vent system resulting in a net inert fuel tank oxygen concentration
Does not need to run on ground or store NEA, eliminates need for compressors or ground service equipment
System only needing to reduce the oxygen concentration below 12% makes sizing more realistic
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8. FAA Simplified Inerting System Block Diagram
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9. System Construction Uses 3 ASMs based on HFM technology
Excepts 350 degree F air from aircraft bleed system through an SOV
Uses a H/x to cool air to 180˚F +/- 10˚F and a filter to condition air
Air is separated ASMs and NEA is plumbed to output valves to control flow, OEA is dumped overboard with H/X cooling air
System flow control is presently configured with low flow orifice and high flow control valve
System controlled by control box in cabin that is connected to system with cable
System built on aluminum pallet for ease of construction and to support a wide variety of installation methods
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10. CAD Rendering of FAA Inerting System
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11. Test Articles – 747 SP Boeing 747SP with fully functioning systems
Decommissioned from airline service and purchased by the FAA for Ground Testing Only
All major systems fully operational
Has independent power for test equipment and instrumentation
Designed inerting system to mount in empty pack bay
Full Complement of Ground Service Equipment
Instrumentation
Aircraft is Fully Instrumented
Oxygen sampling, pressure taps, and thermocouples on system for OBIGGS performance
Thermocouples in Pack Bay
Some Weather Data Available
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12. Test Article - Airbus A320 Airbus A320 Flight Test Vehicle
Original A320 from production start operated by Airbus for the purposes of research and development
Fully Instrumented with extensive DAS capabilities
Was modified to accommodate an inerting system in the cargo bay
Operated out of Airbus, France Flight Test
World class mod and test center
Instrumentation
Aircraft is Fully Instrumented
Oxygen Sampling for OBIGGS performance
Pressure Transducers and Thermocouples on System.
All flight parameters performed
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13. Test Article – NASA 747 SCA Highly modified Boeing 747-100
Reengineered and modified by NASA for the purposes of carrying a Space Shuttle Orbiter for operations and maintenance
Fully operational, standard, fuel system with unmodified pack bay
Operated out of Ellington field - Houston, Texas
Operated by excellent group of test pilots at a top notch operations facility in and maintained by dedicated group of ground service personnel
Instrumentation
Aircraft is Fully Instrumented
Oxygen sampling, pressure taps, and thermocouples on system for OBIGGS performance
Thermocouples in Pack Bay Area
Pressure altitude measured
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14. Measured Results – Ground Testing
Mounted and tested system in the 747 SP ground test article
Operated OBIGGS with static conditions (best as possible) for the purposes of validating the system performance
Focused on the volume flow of 5% and 11% NEA that could be generated with varying ASM pressure
Testing Illustrated
Stable system performance is difficult to achieve in a dynamic aircraft environment
Manufactures data based on general properties not specific ASM
Different measurement techniques gave different results
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15. Measured Results – Single ASM
Compared dynamic ASM performance with static measurements
through out flight cycle on A320 flight test and compared to static lab data
Data comparison generally good with some large discrepancies
Illustrates the difficulty in obtaining stable temperature and pressure during flight test
180 degree F ASM temp frequently unattainable during Airbus testing
Fixed orifice gives variable flow
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16. Measured Results – Single ASM
Calculated bleed air consumption for the A320 flight cycle
Used equation in terms of NEA flow, NEA [O2], and OEA [O2]
Amount of bleed air consumed large but makes sense
Much higher cruise bleed pressure than expected
Stable NEA flow observed is not from stable ASM performance characteristics
Illustrates the relationship between permeability, selectivity, and altitude
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17. Measured Results – Single ASM
Correlated ASM pressure with NEA flow
Compared data for selected parts of A320 testing flight cycle
Not a true correlation because ASM performance is changing
Ascent and Descent cause large variations in ASM performance due to change in altitude / ASM pressure
Cruise data shows a true correlation in the low flow mode
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18. Measured Results – Complete System
Measured static system flow and purity on the 747 SCA test bed at selected altitudes and somewhat stable ASM pressures
Used variable flow valve to vary flow and purity in flight
Some data did not follow trend
Highlights the difficulty in obtaining stable ASM conditions on a flight test aircraft
Stable ASM temperatures a constant battle
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19. Measured Results – Complete System
Dynamic performance during takeoff/ascent and descent/landing portion of flight cycle is least predictable
Analyzed this portion of flight cycle for 3 different tests
Similar ASM pressure observed
Varying but similar ascent and descent profiles
On ascent flow and purity vary for different tests although input conditions are similar
Attributed to unstable ASM temperature due to different warm ups
No adverse effect on system capabilities
On descent flow and purity vary for different tests as expected because of different variable/high flow orifice settings
Bleed air flow nearly constant
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20. Comparison of System Performance During Takeoff
NEA Purity Data
NEA flow Data
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21. Comparison of System Performance During Landing
NEA Purity Data
NEA flow Data
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22. Comparison of System Bleed air Flow During Landing
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23. Summary
FAA used existing technology in an innovative way to develop a near term, simple, solution to fuel tank flammability control
Duplicating static OBIGGS performance data on an aircraft could be problematic, but the system performed as expected
Bleed air consumption should be studied further to examine the penalty associated with high bleed air consumption and potential methods of reducing bleed air consumption
Measurable performance variations observed at the start of system attributed to different warm-up times did not hamper system from reducing ullage oxygen concentration
Bleed air consumption remained constant after the system was sufficiently warmed-up even when varying flow and purity
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24. The Fourth Triennial International Aircraft Fire and Cabin Safety
Research Conference
The Fourth Triennial International Aircraft Fire and Cabin Safety
Research Conference
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