Inerting Systems for Commercial Airplane Fuel Tanks Alan

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

Inerting Systems for Commercial Airplane Fuel Tanks Summary • • • 2 Brief History System Overview Airplane Safety Considerations Hot Day Operations Goal Boeing Philosophy

Inerting Systems for Commercial Airplane Fuel Tanks Brief History • Military use of fuel tank inerting • Designed for military threats – Primary protection for routine combat threats – Full time inerting / all tanks – 1950 s “visible light” justified 9% or 9. 8% O 2 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 3

Inerting Systems for Commercial Airplane Fuel Tanks Brief History • FAA Inerting Study in 1970 s – 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 4

Inerting Systems for Commercial Airplane Fuel Tanks Brief History • Changes that enable a cost effective, practical FRS • FAA Testing validated that an Inert Benchmark of 12% O 2 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 5

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

Inerting Systems for Commercial Airplane Fuel Tanks System Overview • Airplane bleed flow/pressure source of air • Bleed air typically up to 450 F – 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 O 2 from air to generate NEA • Purity dependant on pressure available • OEA exhausted overboard • NEA supplied to tank 7

Inerting Systems for Commercial Airplane Fuel Tanks 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 8

Inerting Systems for Commercial Airplane Fuel Tanks 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 9

Inerting Systems for Commercial Airplane Fuel Tanks 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 – 450 F bleed system indirectly connected to fuel tank – System must absolutely preclude 450 F 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 10

Inerting Systems for Commercial Airplane Fuel Tanks 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 11

Inerting Systems for Commercial Airplane Fuel Tanks Hot Day Operations • Unexplained accidents occurred on 80 F 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 80 F • 3% Climb 80 F • Ground requirement will likely be system size driver 12

Inerting Systems for Commercial Airplane Fuel Tanks 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 13

Inerting Systems for Commercial Airplane Fuel Tanks 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 – 747 -400 4 th Quarter 2005 – 737 NG 2 nd Quarter 2006 – 777, 737 -3/4/500, 767 and 757 to follow – NGS is standard for all tanks on 7 E 7 • NGS as an additional level of protection is the future for Boeing airplanes 14

Inerting Systems for Commercial Airplane Fuel Tanks The Fourth Triennial International Aircraft Fire and Cabin Safety Research Conference 15