# Presentation: 148380

## Inerting Systems for Commercial Airplane Fuel Tanks

**Alan Grim**
**Boeing Commercial Airplanes**
**November 18, 2004**

## Summary 

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

## 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**

## 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**

## 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**

## System Overview

- Simplified to protect Boeing Proprietary Data

**Witness **
**Drain /**** ****Test Port**

**NGS Shut-off****valve**

**T**

**Ram Cooling **
**Flow via **
**Existing **
**ECS Scoop**

**NEA to Tank**

**Bleed Flow**

**System Control**
**  **

**Cooling flow and ****Oxygen**** ****Exhaust**** Overboard**

**Filter**

**System Status / Indication**

**Float Valve**
** ****        **

**Center**
**Fuel Tank**

**High Flow Descent Control Valve**

**External Inputs**

**Ozone**
**Converter**

**Waste OEA to Cooling Exhaust**

**     ****Heat Exchanger**

**Nitrogen Generation System (NGS)**

- NEA – Nitrogen Enriched Air
- OEA – Oxygen Enriched Air

## 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**

## 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**

##  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**

## 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**

## 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**

## 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**

**Notes:**
ARAC said reduce to that of the wing.  Can meet without addressing hot day ground or climb ops.

## 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**

## 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**
**737NG 2****nd**** 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**

## The Fourth Triennial International Aircraft Fire and Cabin Safety 

**The Fourth Triennial ****International Aircraft Fire and Cabin Safety **
**Research Conference**

**The Fourth Triennial ****International Aircraft Fire and Cabin Safety **
**Research Conference**