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Inerting Systems for Commercial Airplane Fuel Tanks

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Presentation on theme: "Inerting Systems for Commercial Airplane Fuel Tanks"— Presentation transcript:

1 Inerting Systems for Commercial Airplane Fuel Tanks
Alan Grim Boeing Commercial Airplanes November 18, 2004 1

2 Summary Brief History System Overview Airplane Safety Considerations
Hot Day Operations Goal Boeing Philosophy

3 Brief History Military use of fuel tank inerting
Designed for military threats Primary protection for routine combat threats Full time inerting / all tanks 1950s “visible light” justified 9% or 9.8% O2 inert definition Various implementations including liquid nitrogen storage, pressure swing absorption, halon, etc Typically low reliability Typically heavy Not included in non-front line military aircraft Not practical for commercial application

4 Brief History FAA Inerting Study in 1970s – Not practical
1996 NTSB Recommendation following Flight 800 accident FAA initiated ARAC teams to study flammability reduction and inerting for commercial use 1998 ARAC Studied flammability reduction options Recommended rule for new design to reduce flammability 2001 ARAC focused on Inerting Ground based On board in flight Recommended further development of onboard generation System still not practical in 2001 Cost, weight, reliability all issues

5 Brief History Changes that enable a cost effective, practical FRS
FAA Testing validated that an Inert Benchmark of 12% O2 precludes significant pressure rise for vast majority of commercial conditions Use of Hollow Fiber Membranes Applying an average risk fleet wide safety assessment (Monte Carlo) Reducing flammability exposure to levels at least equivalent to wing tanks will provide an order of magnitude improvement Defining the system as non-critical to airplane operations Use of inerting as an additional level of protection to ignition protection Focus on high flammability exposure center wing tanks only

6 Cooling flow and Oxygen Exhaust Overboard
System Overview Nitrogen Generation System (NGS) External Inputs System Control System Status / Indication Float Valve Center Fuel Tank Ram Cooling Flow via Existing ECS Scoop High Flow Descent Control Valve NGS Shut-off valve T Bleed Flow Ozone Converter Heat Exchanger Filter Air Separation Module NEA to Tank Waste OEA to Cooling Exhaust Witness Drain / Test Port Cooling flow and Oxygen Exhaust Overboard NEA – Nitrogen Enriched Air OEA – Oxygen Enriched Air Simplified to protect Boeing Proprietary Data

7 System Overview Airplane bleed flow/pressure source of air
Bleed air typically up to 450F To hot for current fiber to handle ASM requires warm air with as much pressure as available Cooling of Bleed air required Utilize ECS ram air for cooling source Control temperature to ASM for optimum performance ASM separates O2 from air to generate NEA Purity dependant on pressure available OEA exhausted overboard NEA supplied to tank

8 System Overview Multiple flow modes used to reduce bleed consumption
Low flow used in climb and cruise Inerting performance good Bleed flow conserved – directly related to fuel burn High flow used during descent Vent system modifications may be required Boeing Puget Sound airplanes vent to both wing tips Condition dubbed “cross-venting” results Design change required

9 System Overview Simple distribution system required to remain practical System size dependent on even distribution of NEA Tank structure will have an effect on distribution Discrete vent points will affect design

10 Safety Considerations
Design Precautions that must be addressed to preclude creating additional hazards Prevent potential new ignition sources inside fuel tank Bond for electrostatics Prevent lightning energy entering tank 450F bleed system indirectly connected to fuel tank System must absolutely preclude 450F air from reaching tank Requires redundant independent shutoff methods Minimize Impact of Bleed air use on existing systems Cabin pressurization Ability to evacuate smoke from cabin Engine performance

11 Safety Considerations
Hazards to maintenance personnel Limit NEA concentration to protect maintenance personnel Fuel tank Confined spaces where NGS is installed or routed Modifications to fuel tank vent system must not result in tank over/under pressure conditions NGS failures Rapid climb/emergency descent Refueling failure cases

12 Hot Day Operations Unexplained accidents occurred on 80F ambient temps and greater 2 ground incidents and 1 climb incident Analysis shows significant flammability exposure on 80+ F days on ground and in climb FAA Proposed 747 Special Condition covers this scenario 3% Fleet Average 3% Ground 80F 3% Climb 80F Ground requirement will likely be system size driver ARAC said reduce to that of the wing. Can meet without addressing hot day ground or climb ops.

13 Goal Practical System to provide order of magnitude improvement in Fuel Tank Safety Design and install a practical and effective system that protects the airplane Address ground and climb operations on warm days Designed to achieve 10 day MMEL Classification Minimal bleed air use impact on fuel burn Minimize weight impact Ensure Service Ready Do not introduce any new hazards No new ignition sources in fuel tank No hazards to people

14 Boeing Philosophy Safe and Efficient Global Air Transportation
Minimize potential for future accidents NGS is a safety enhancement Ignition protection alone has achieved its maturity limits NGS provides a secondary level of protection to mitigate human factors in design, manufacture, operation and maintenance Leading the Effort to Develop NGS Practical design Service Ready Systems available th Quarter 2005 737NG 2nd Quarter 2006 777, 737-3/4/500, 767 and 757 to follow NGS is standard for all tanks on 7E7 NGS as an additional level of protection is the future for Boeing airplanes

15 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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