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