Development and Testing of the FAA Simplified Fuel Tank Inerting System

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

2. Outline • Background • 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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

8. FAA Simplified Inerting System Block Diagram AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

10. CAD Rendering of FAA Inerting System AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

20. Comparison of System Performance During Takeoff NEA Purity Data NEA flow Data AAR-440 Fire Safety R&D

21. Comparison of System Performance During Landing NEA Purity Data NEA flow Data AAR-440 Fire Safety R&D

22. Comparison of System Bleed air Flow During Landing AAR-440 Fire Safety R&D

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 AAR-440 Fire Safety R&D

24. The Fourth Triennial International Aircraft Fire and Cabin Safety Research Conference The Fourth Triennial International Aircraft Fire and Cabin Safety Research Conference AAR-440 Fire Safety R&D