TWA 800 INVESTIGATION

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TWA 800 INVESTIGATION

• Merritt M. Birky, Ph.D.
• National Transportation Safety Board
• Office of Research and Engineering
• Flammability Program for
• TWA 800 Accident Investigation

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Reconstruction
STA 1500
STA 520
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747-100 CWT
RS
SWB1
MS
Front Spar
SWB2
SWB3
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INVESTIGATION OBJECTIVE/APPROACH

• Determine cause of explosion to prevent future
  accidents of this type
• Approach-
• Examine hardware in accident airplane
• Examine wiring in similar airplanes
• Did flight tests to determine conditions in CWT
• Do Jet A flammability testing

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FLAMMABILITY OF JET A

• FLIGHT TEST
• vapor sampling and temperatures
• LABORATORY EXPLOSION TESTING
• VAPOR CHEMISTRY OF JET A
• 1/4 SCALE EXPLOSION STUDY
• MODELING OF EXPLOSIONS
• FULL SCALE EXPLOSION TESTING

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TESTING OBJECTIVES

• DETERMINE IGNITION SOURCE OR
• DETERMINE LOCATION OF IGNITION SOURCE
• DETERMINE THE FIRE/EXPLOSION PROPERTIES OF JET A
• DETERMINE IGNITION ENERGY

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FLIGHT TESTS

• SAFETY BOARD/BOEING
• OBJECTIVES
• DETERMINE CONDITIONS INSIDE THE CWT
• COLLECT VAPOR SAMPLES DURING FLIGHT
• DETERMINE TEMPERATURE UNDER CWT

NTSB
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TWA 800 INVESTIGATIONFLIGHT TEST AIRCRAFT

• Evergreen Airlines
• 747-121
• Boeing Line number 106

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FLIGHT TEST INSTRUMENTATION

• Boeing Commercial Airplane Company
• Instrumentation, installation and flight crew
• 153 temperature sensors
• pressure sensors
• vibration sensors
• vapor sampling

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FLIGHT TEST PROGRAMOVERVIEW

• CWT VAPOR SAMPLES
• During Taxi
• 10,000 feet
• 14,000 feet
• CWT LIQUID SAMPLES
• Before and after flight

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FLIGHT TEST VAPOR SAMPLING

• UN. OF NEVADA, DESERT RESEARCH INSTITUTE
• DR. JOHN SAGEBIEL
• OBJECTIVE
• DETERMINE CHEMICAL COMPOSITION OF VAPORS IN CWT
  DURING FLIGHT

NTSB
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Center Wing Tank (CWT) Nomenclature

• BAY 1 - Between spanwise beams 2 and 3
• BAY 2 - Between spanwise beam 2 and mid spar
• MID BAYS - Between mid spar and spanwise beam 1
• AFT BAYS - Between spanwise beams 1 and rear spar
• ULLAGE - Space in fuel tank above the liquid
  fuel, occupied by fuel vapor

S
SW3
SW2
SW1
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Center Wing Tank Heating
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ALTITUDE DATA TWA 800 EMULATION FLIGHT
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(No Transcript)
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Fuel to Air Mass and Mole Ratios
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TWA 800 EMULATION FLIGHTCWT Ullage Temps at
Start of Taxi
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VAPOR PRESSURE MEASUREMENTS

• UN. OF NEVADA, RENO
• MR. JIM WOODROW
• OBJECTIVES
• DETERMINE VAPOR PRESSURE AS A FUNCTION OF
  TEMPERATURE AND ULLAGE/LIQUID RATIO
• CHEMICALLY CHARACTERIZE THE VAPORS

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LABORATORY EXPLOSION TESTING

• CALIFORNIA INSTITUTE OF TECHNOLOGY
• PROF. JOSEPH SHEPHERD
• OBJECTIVES
• MEASURE RATE OF PRESSURE RISE
• PEAK PRESSURE
• MINIMUM IGNITION ENERGY

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Vapor Pressure of LAX Jet A
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Pressure Histories
time (s)
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Jet A Composition
Woodrow data on Reno Jet A
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1/4 SCALE EXPLOSION TESTING

• OBJECTIVES
• STUDY EFFECTS OF IGNITION LOCATION ON PRESSURE
  DYANMICS
• STUDY THE EFFECTS OF FLAME COMMUNICATIONS BETWEEN
  COMPARMENTS

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Why do scale model experiments?
Goal
Develop insight into a complex combustion problem

• Issues that we could not examine in the lab
• motion of flames between bays
• acceleration of flames by turbulence in bays
• dispersion of liquid jet fuel as spray or mist
• failure of SWB3, FS, access panel in SWB2
• Test cases for numerical simulation of flames
• Step toward goal of finding ignition source

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Actual Test Fixture
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Simulant Fuel vs. Jet A Vapor
Idea Match pressure rise and flame speed of Jet
A created from a liquid layer (scaled to 50 gal
in CWT) at 50 C
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Flame Ignition and Growth
spark
Jet A simulant
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Failure of Beams and Spars
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Ignition Locations

• Parametric study
• Fuel probe, compensator, terminal block
  locations

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Test 04 - Pressure Data
4.5
4
bay 6
3.5
bay 5
3
bay 4
2.5
bay 3
pressure rise (bar)
2
bay 2
1.5
bay 1
1
0.5
0
0.1
0.12
0.14
0.16
0.18
0.2
0.22
0.24
time (s)
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1/4 Scale with Jet A on Bottom
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COMPUTER MODELING

• OBJECTIVES
• PREDICT EFFECTS OF IGNITION IN DIFFERENT
  LOCATIONS IN CWT
• PREDICT EFFECTS OF COMMUNICATION BETWEEN BAYS

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COMPUTER MODELING

• SANDIA LABORATORIES
• DR. MELVIN BAER
• CHRISTIAN MICKELSON RESEARCH
• DR. KEES VAN WINGERTEN
• COMBUSTION DYNAMICS
• DR. PAUL THIBAULT

NTSB
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Recent Activities

• Repeatability 1/4 scale testing
• 1/4 Scale tests with Jet A fuel
• Sensitivity Analysis on Ignition Location
• Development of Tank/AC Thermal Model

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Primary Objective

• Determine most probable ignition location based
  on
• Observed Damages
• Fuel/Temperature distribution obtained from
  flight test data

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Approach
Rule Based Scenario Analysis
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Approach
Rule Based Scenario Analysis
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BRUNTINGTHROPE TEST

• NTSB/DERA
• OBJECTIVES
• DETERMINE SIGNATURE OF SMALL EXPLOSIVE CHARGES ON
  CWT
• DETERMINE EFFECTS OF EXPLODING A HYDROCARBON GAS
  IN CWT

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What have we learned?

• Combustion occurs quickly in other bays once
  ignition bay burns
• Ignition location influence observable but no
  smoking gun yet
• Extremely challenging inverse problem
• Where was fuel vapor?
• Numerical simulation of full-scale explosion
• Numerical simulation of structural failure
• Quenching of flame between bays appears important

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Activities in Progress

• Explore Feasibility of coupling CFD model with
  Structural Model
• Analysis of Jet A 1/4 Scale Tests
• Analysis of Flame Quenching