An Evaluation of the Flammability of 

Aircraft Wiring 

Patricia Cahill 

December 2004 

DOT/FAA/AR-TN04/32 

This document is available to the public through the National 

Technical Information Service (NTIS), Springfield, Virginia 22161. 

U.S. Department of Transportation 

Federal Aviation Administration

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NOTICE 

This document is disseminated under the sponsorship of the U.S. 

Department of Transportation in the interest of information exchange. The 

United States Government assumes no liability for the contents or use 

thereof. The United States Government does not endorse products or 

manufacturers. Trade or manufacturer's names appear herein solely 

because they are considered essential to the objective of this report. This 

document does not constitute FAA certification policy. Consult your local 

FAA aircraft certification office as to its use. 

This report is available at the Federal Aviation Administration William J. 

Hughes Technical Center’s Full-Text Technical Reports page: 

actlibrary.tc.faa.gov in Adobe Acrobat portable document format (PDF). 
Technical Report Documentation Page 

1. Report No.

DOT/FAA/AR-TN04/32 

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle

AN EVALUATION OF THE FLAMMABILITY OF AIRCRAFT WIRING 

5. Report Date 

December 2004

6. Performing Organization Code

ATO-P 

7. Author(s)

Patricia Cahill 

8. Performing Organization Report No.

9. Performing Organization Name and Address

Federal Aviation Administration 

William J. Hughes Technical Center 

Airport and Aircraft Safety 

10. Work Unit No. (TRAIS)

Research and Development Division 

Fire Safety Branch 

Atlantic City International Airport, NJ 08405 

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

U.S. Department of Transportation 

Federal Aviation Administration

13. Type of Report and Period Covered

Technical Note 

Office of Aviation Research 

Washington, DC 20591 

14. Sponsoring Agency Code

ANM-100 

15. Supplementary Notes

16. Abstract

This report discusses the flammability tests conducted on aviation and nonaviation electrical wiring that were performed to reevaluate the effectiveness of the current Federal Aviation Administration (FAA)-mandated 60° Bunsen burner flammability test 

requirement for aircraft wiring. The evaluation included a 60° flammability test, an intermediate-scale vertical flammability test, 

and an intermediate-scale cabin attic flammability test. Test results showed that the 60° single wire Bunsen burner flammability 

test may not be adequate to qualify wire when bundled and subjected to a severe ignition source. 

17. Key Words

Aircraft wiring, 60° flammability test, Intermediate-scale cabin 

attic tests 

18. Distribution Statement

This document is available to the public through the National 

Technical Information Service (NTIS), Springfield, Virginia 

22161.

19. Security Classif. (of this report)

Unclassified 

20. Security Classif. (of this page)

Unclassified 

21. No. of Pages

39 

22. Price

Form DOT F1700.7 (8-72) Reproduction of completed page authorized 
ACKNOWLEDGEMENTS 

The author would like to acknowledge Brian Conover of Galaxy Scientific Corporation for all 

his work on this project. His efforts were invaluable. I would also like to acknowledge Frank 

Hahn of the Galaxy Scientific Corporation for his excellent assistance with the visual 

presentation of this report. 

iii/iv
TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY ix 

INTRODUCTION 1

Purpose 1 

Background 1

Discussion 2

TEST PROGRAM 3 

Sixty Degree Flammability Tests 3 

Intermediate-Scale Vertical Flammability Tests 4 

Intermediate-Scale Cabin Attic Flammability Tests (Configuration 1) 6 

Instrumentation 7

Test Article and Wire Bundle Configuration 8 

Intermediate-Scale Cabin Attic Flammability Test Results 10 

Intermediate-Scale Cabin Attic Flammability Tests (Configuration 2) 22 

Intermediate-Scale Cabin Attic Flammability Test Results (Configuration 2) 23 

CONCLUSIONS 31

REFERENCES 31

LIST OF FIGURES

Figure Page 

1 Intermediate-Scale Vertical Flammability Test Rig and Sample Setup 5 

2 Intermediate-Scale Wire Test Article 6 

3 Thermocouple Placement 7 

4 Gardon Gauge Placement 8 

5 Test Article Configuration 9 

6 Foam Block Ignition 9 

7 Baseline Temperature and Heat Flux—Polyimide Blankets 10 

8 Thermocouple 3 11 

9 Thermocouple 4 12 

10 Heat Flux Data 12 

11 Ignition of PTFE/Polyimide/PTFE 13 

12 Flameout of PTFE/Polyimide/PTFE 13 

v
13 Ignition of Tefzel 14

14 Flameout of Tefzel 14

15 Ignition of Spec 2112 15 

16 Flameout of Spec 2112 15 

17 Ignition of Riser Cable (A) 16 

18 Test Progression of Riser Cable (A), View 1 16 

19 Test Progression of Riser Cable (A), View 2 17 

20 Test Progression of Riser Cable (A), View 3 17 

21 Flameout of Riser Cable (A) 18 

22 Ignition of PVC/Nylon 18 

23 Test Progression of PVC/Nylon, View 1 19 

24 Test Progression of PVC/Nylon, View 2 19 

25 Test Progression PVC/Nylon, View 3 20 

26 Test Progression of PVC/Nylon View 4 20 

27 Test Progression of PVC/Nylon, View 5 21 

28 Flameout of PVC/Nylon Test 21 

29 Intermediate-Scale Cabin Attic Flammability Tests Configuration 2 22 

30 PTFE/Polyimide/PTFE Temperature and Heat Flux Profile 23 

31 Riser Cable (A) Temperature and Heat Flux Profile 23 

32 Ignition of PTFE/Polyimide/PTFE 24 

33 Test Progression of PTFE/Polyimide/PTFE, View 1 25 

34 Test Progression PTFE/Polyimide/PTFE, View 2 25 

35 Flameout of PTFE/Polyimide/PTFE 26 

36 Ignition of Riser Cable (A) 26 

37 Test Progression of Riser Cable (A), View 1 27 

38 Test Progression of Riser Cable (A), View 2 27 

39 Test Progression of Riser cable (A), View 3 28 

40 Test Progression of Riser Cable (A), View 4 28 

41 Test Progression of Riser Cable (A), View 5 29 

42 Test Progression of Riser Cable (A), View 6 29 

43 Flameout of Riser Cable (A), Cross View 30 

44 Flameout of Riser Cable (A), Lengthwise View 30 

LIST OF TABLES 

Table Page 

1 Wire Description 3 

2 Sixty Degree Flammability Test Results 4 

3 Intermediate-Scale Vertical Flammability Test Results 5 

4 Intermediate-Scale Cabin Attic Flammability Test Results 10 

vi
LIST OF ACRONYMS

AWG American wire gauge 

cc Cubic centimeter 

CFR Code of Federal Regulations 

ETFE Ethylene tetrafluoroethylene 

FAA Federal Aviation Administration 

FEP Fluorinated ethylene propylene 

ml milliliter 

pcf Pounds per cubic foot 

PTFE Polytetrafluoroethylene

PVC Polyvinyl chloride 

vii/viii 
EXECUTIVE SUMMARY

This report discusses the flammability tests conducted on aviation and nonaviation electrical 

wiring that were performed to evaluate the effectiveness of the current Federal Aviation 

Administration (FAA)-mandated 60° Bunsen burner flammability test requirement for aircraft

wiring. This work was part of the FAA’s program to re-evaluate the flammability test methods 

specified in Title 14 Code of Federal Regulations 25.853, with an emphasis on those methods

used to test the flammability of materials in hidden areas of the aircraft. Hidden areas refer to 

those areas not easily accessible to the flight crew, such as the attic above the cabin ceiling, 

beneath the floor, and areas in or around the lavatories. The tests included in this study were the 

60° flammability test, an intermediate-scale vertical flammability test, and an intermediate-scale

cabin attic flammability test. While some correlation existed between the 60° flammability test

and the intermediate-scale cabin attic flammability tests, it appeared to be limited to the most 

fire-resistant samples. No correlation existed for materials that had greater burn lengths or

marginally passed the 60° flammability test. In fact, one particular material that passed the 60°

flammability test performed so poorly in the intermediate-scale cabin attic flammability test, 

with significant flame propagation and dense smoke, that test personnel were forced to leave the

test area. Hence, the test results showed that the 60° flammability test may not disqualify wiring 

that propagates a fire when subjected to a severe ignition source. 

ix/x
INTRODUCTION 

PURPOSE. 

The purpose of this report is to describe experiments that were conducted to determine if the 

current Federal Aviation Administration (FAA) mandated 60° flammability test requirement for 

electrical wiring, as specified in Title 14 Code of Federal Regulations (CFR) 25.869, is adequate. 

BACKGROUND. 

Life-threatening, in-flight fires usually originate in hidden areas of the airplane, such as the attic

above the cabin ceiling, beneath the floor, in or around the lavatories, or at similar locations that 

are not easily accessible by the crew. Because of the incidence of in-flight fires in recent years, 

the FAA is examining the adequacy of its flammability test requirements for all hidden materials,

which include thermal acoustic insulation, electrical wiring, and heating, ventilation, and air 

conditioning ducts. As detailed below, the focus of this examination is the performance of hidden 

materials, that are compliant with the current FAA requirements, when subjected to a severe 

ignition source during intermediate- and large-scale fire tests. The test requirement is deemed to

be inadequate if currently compliant materials are found to ignite and propagate a fire. By 

requiring that hidden materials be capable of resisting this elevated fire threat, a significant

upgrade in the fire resistance of hidden area materials will be realized. Aircraft lined with

materials that are more fire resistant will reduce the incidence of in-flight fires. 

In July 2003, the FAA issued the following regulation: “Improved Flammability Standards for 

Thermal/Acoustic Insulation Materials Used in Transport Category Airplanes.” This regulation

upgraded the flammability standards for aviation thermal/acoustic insulation materials. It was 

prompted by a number of incidents, including the in-flight fire that caused the Swissair MD-11 

accident in 1998, and prior research and development conducted by the FAA. The International 

Aircraft Materials Fire Test Working Group, sponsored by the Fire Safety Branch at the FAA 

William J. Hughes Technical Center, had formed a working group that performed round-robin 

flammability tests on thermal/acoustic insulation materials. The results of this testing showed that 

the FAA-mandated test for these materials, a vertical Bunsen burner test specified in CFR 25.853, 

did not adequately characterize the flammability of these materials [1]. This test was replaced by 

the more stringent flame propagation test specified in the new regulation, which became effective 

on September 2, 2003. 

The research and development work that led to the new flame propagation test method included 

bench- and intermediate-scale flammability tests. The intermediate-scale flammability tests were

conducted in a fuselage section that simulated the attic area above the aircraft cabin ceiling. 

A severe ignition source was developed, which consisted of a heptane-soaked polyurethane foam 

block. From the numerous tests conducted, the foam block was shown to be a highly repeatable 

ignition source, and was adopted as the standard ignition source for all in-flight hidden fire 

tests [2]. 

1
The intermediate-scale cabin attic flammability tests conducted on thermal/acoustic insulation

were critical in that the results significantly discriminated between the flammability behavior of

different materials. One particular film cover material, metallized Mylar, which passed the

FAA-mandated 12-second Bunsen burner test most of the time, performed poorly in the 

intermediate-scale cabin attic flammability test. There was significant flame spread, with the bulk 

of the material consumed. This test was the driving force in raising the level of flammability

safety to the more stringent level imposed by the foam block ignition source. 

The genesis for the current FAA flammability test requirement for electrical wiring was

Amendment 25-32, effective May 1,1972, which added a new section 25.1359(d), that applied the 

flammability requirements of Appendix F of Part 25 to wire insulation used in aircraft. Section 

25.1359(d) is now Section 25.869 in 14 CFR Part 25. The mandated test specifies that insulation 

on electrical wire or cable installed in any area of the fuselage must be self-extinguishing when 

subjected to the 60° flammability test specified in Part Ι of Appendix F. The requirements state 

that the average burn length may not exceed 3 inches and the average flame time after removal of 

the 3-inch Bunsen burner flame source may not exceed 30 seconds. Drippings from the test 

specimen may not continue to flame for more than an average of 3 seconds after falling. This is 

the only test the FAA mandates for aircraft wire flammability.

DISCUSSION. 

To evaluate the effectiveness of the 60° flammability test in characterizing the flammability of 

wire, 12 types of wire were selected for testing. Some of these wires were subjected to more 

realistic intermediate-scale cabin attic flammability tests, and the data were compared to the

results of the 60° flammability tests. The objective was to see if a correlation existed between the

test results. Six of the wires were aviation-grade and six were communication cables. 

Nonaviation wires were included in this study because the purpose was to evaluate the 60°

flammability test method and not the material. A description of the wires used in the tests is 

given in table 1. 

The aviation-grade wires shown in table 1 are rated at 150°C, except the polyvinyl chloride 

(PVC)/nylon wire, which is rated at 105°C. This 150°C rating is primarily due to the tin-plated

copper conductor. As an example, polyimide insulation over a nickel-plated copper conductor

would be rated at 260°C. PVC/nylon wire was included in this study because of its widespread 

use before May 1972. It does not pass the 60° flammability test; however, there are in-service

airplanes with PVC/nylon wire. PVC/nylon-wired airplanes are referred to as earlier airplanes. 

2
TABLE 1. WIRE DESCRIPTION 

Wire/Cable Description

Polyimide Aviation-grade 20 AWG 150°C rated 

PVC/nylon Aviation-grade 20 AWG, 105°C rated 

Tefzel ETFE Aviation-grade 20 AWG, 150°C rated 

X-linked Tefzel ETFE Aviation-grade 20 AWG, 150°C rated 

PTFE/polyimide/PTFE Aviation-grade 20 AWG, 150°C rated 

Spec 2112 cross-linked polyalkene Aviation-grade 20 AWG, 150°C rated 

Plenum cable (A) 4 twisted pair (FEP-insulated) 24 AWG, loaded vinyl 

jacket, 60°C rated 

Riser cable (A) 4 twisted pair, 24 AWG, hybrid PVC jacket, 60°C rated 

Telecommunication cable Zero halogen, 4 twisted pair, 24 AWG, temperature rating 

unknown 

Plenum cable Limited combustible 4 twisted pair (FEP-insulated) 24 

AWG, FEP jacket, 200°C 

Riser cable 4 twisted pair, 24 AWG, PVC jacket, 75°C rated 

Plenum cable 4 twisted pair, 24 AWG, FEP jacket 

TEST PROGRAM

SIXTY DEGREE FLAMMABILITY TESTS. 

The results of the 60° flammability tests are shown in table 2. The data show that all the wires

and cables passed this test except PVC/nylon wire, which exhibited the longest burn length and 

after-flame time, and the zero halogen cable. Note that the zero halogen cable had an average 

after flame of 60.3 seconds and an average burn length of 3.1 inches, which barely exceeded the 

3-inch requirement. These samples did not propagate the flame but continuously burned in place 

(evolving gases) with no drippings. The 60° flammability test does not discriminate very well 

between the performance of different materials. For those materials that were compliant with the

60° flammability test requirement, the difference in burn length for the best material

(PTFE/polyimide/PTFE) and the worst materials (plenum cable A, riser cable A, and riser cable

CMR CAT 5E) was only 1.3 inches. Only one material exhibited after flame (Spec 2112), and 

the value was very small (1.7 inches) with no drippings. Therefore, to better discriminate 

between different electrical wiring materials, an intermediate-scale vertical flammability test rig 

was employed. 

3
TABLE 2. SIXTY DEGREE FLAMMABILITY TEST RESULTS 

(Average of three tests) 

Wire/Cable 

Burn Length 

(inches) 

After Flame 

(seconds) Drippings 

Polyimide 1.5 0 0

PVC/nylon 14.8 121 0

Tefzel 2 0 0

X-linked Tefzel 1.8 0 0

PTFE/polyimide/PTFE 1.2 0 0

Spec 2112 2.1 1.7 0 

Plenum cable (A) 2.5 0 0 

Riser cable (A) 2.5 0 0 

Telecommunication cable zero halogen 3.1 60.3 0 

Limited combustible CMP CAT 6 2 0 0 

Riser cable CMR CAT 5E 2.5 0 0 

Plenum cable CAT 5-E 1.8 0 0 

INTERMEDIATE-SCALE VERTICAL FLAMMABILITY TESTS. 

The intermediate-scale vertical flammability test is not a standard test and, therefore, has no pass 

or fail criteria. All 12 wire types were tested and evaluated for burn length, after flame, and flame

time of drippings. Unlike the 60° flammability test that evaluates individual wires, the wires in 

this test were tied together in bundles. The 20 AWG aviation-grade wires were tied into bundles 

of 25, and the larger telecommunication cables into bundles of 10. Figure 1 shows the test rig and 

sample setup. Ten cubic centimeters (cc) of denatured alcohol were poured on a polyurethane 

block and 25 cc was added to the fuel pan that holds the polyurethane block. The bottom of the

48-inch-long wire bundle was 1 inch above the top of the block. Metallized Tedlar film cover 

over two layers of 0.34 pound per cubic foot (pcf) fiberglass insulation was selected as the backer 

material because it shrinks away from the heat source and does not propagate flame. Hence, it did 

not influence the test results. The polyurethane block was ignited and allowed to burn until

consumed. The test was terminated upon extinguishment of burning wires, if applicable, or block 

extinguishment. The burn length, after flame, and drippings were monitored and recorded. The 

results are presented in table 3. 

4
Pan with 4 holes, 

which holds 

25 cc of 

denatured alcohol. 

Peg that holds

the polyurethane

block in place.

Safety wire used to

attach the wire

bundle to the frame.

Safety 

wire 

Block and 

fuel pan 

Clamps used to attach 

insulation to the 

frame. There are 6

clamps used; 3 on

each side. 

Wire bundle attached 

to insulation by 

nylon tie wraps 

and safety wires. 

Polyurethane

Block 

4′′ × 9′′

FIGURE 1. INTERMEDIATE-SCALE VERTICAL FLAMMABILITY TEST RIG AND 

SAMPLE SETUP 

TABLE 3. INTERMEDIATE-SCALE VERTICAL FLAMMABILITY TEST RESULTS 

(One test) 

Wire Type 

Burn Length 

(inches) 

After Flame

(seconds) 

Drippings 

(seconds) 

Polyimide 8 0 0

PVC/nylon 28 45 0

Tefzel 14 0 0

X-linked Tefzel 12 0 0

PTFE/polyimide/PTFE 8.5 0 0

Spec 2112 10.5 0 0 

Plenum cable (A) 29 0 0 

Riser cable (A) 31 0 0 

Telecommunication cable–zero halogen 44 140 10 

Limited combustible CMP CAT 6 7.5 0 0 

Riser cable CMR CAT 5E 8 0 0 

Plenum cable CAT 5E 5 0 0 

5
The data in table 3 show better discrimination in the fire performance of the wire samples than 

was exhibited by the 60° flammability test (see table 2). Burn lengths varied by about a factor of 

6 (5 inches to 31 inches) versus only a factor of about 2 (1.2 inches to 2.5 inches) for compliant 

wire samples. It appears that the wire samples with a burn length of 2 inches or less in the 60°

flammability test were relatively good performers in the intermediate-scale vertical flammability

test. For samples with a burn length greater than 2 inches, the behavior in the intermediate-scale 

vertical flammability test is more variable. For example, the plenum cable (A), riser cable (A),

and riser cable CMR CAT 5E in the 60° flammability test all had burn lengths of 2.5 inches, yet 

their intermediate-scale vertical burn flammability test lengths were 29 inches, 31 inches, and 8

inches, respectively. Plenum cable (A) and riser cable (A) also had intermediate-scale vertical

flammability test burn lengths comparable to PVC/nylon, but PVC/nylon easily failed the 60°

flammability test. Thus, it appears that some wire samples with a 60° flammability test burn

length greater than 2 inches may be poor performers under larger-scale flammability test

conditions. These samples would, of course be compliant with the current 60° flammability test 

criteria for aircraft wiring, raising concerns regarding the adequacy of these test criteria. 

INTERMEDIATE-SCALE CABIN ATTIC FLAMMABILITY TESTS (CONFIGURATION 1). 

In this series of tests, 5 of the original 12 types of wire and cable (PTFE/polyimide/PTFE, 

Tefzel, Spec 2112, riser cable (A), and PVC/nylon) were evaluated. These wire and cable 

constructions were selected based on the data from the 60° and intermediate-scale vertical 

flammability tests and their widespread use in commercial and general aviation aircraft. The 

PTFE/polyimide/PTFE construction was the overall best performer. The Tefzel and Spec 2112 

constructions were selected because they are widely used. The PVC/nylon construction was 

included as a worst-case scenario and the riser cable (A) because of the excessive burn length

found in the intermediate-scale vertical flammability test. Baseline tests were also performed 

with polyimide/fiberglass insulation blankets and no wire. 

The test article, shown in figure 2, is a section of a narrow-body aircraft that measures 11 ft. 2 in. 

long and 10 ft. 7 in. wide. The test article is open at both ends. 

FIGURE 2. INTERMEDIATE-SCALE WIRE TEST ARTICLE 

6
INSTRUMENTATION. 

Ten 1/16-inch Inconel 600 sheathed thermocouples rated at 2100°F were placed in the test article.

They were inserted through the top of the test article and linked to the data acquisition system. 

All thermocouples were positioned above the wire bundles to detect any flame spread on the wire. 

Figure 3 shows the placement and identifies the thermocouples by number. A Vatell watercooled Gardon gauge, which measures radiant heat flux, was placed at the end of the test article, 

as shown in figure 4. The Gardon gauge was 56 1/2 inches on the diagonal from the ignition 

source. 

1. Center Top 6. Right Middle 

2. Center Top Middle 7. Right Bottom

3. Center Bottom Middle 8. Left Top 

4. Center Bottom 9. Left Middle 

5. Right Top 10. Left Bottom

FIGURE 3. THERMOCOUPLE PLACEMENT 

7
FIGURE 4. GARDON GAUGE PLACEMENT

TEST ARTICLE AND WIRE BUNDLE CONFIGURATION.

Four polyimide blankets measuring 24 by 66 inches were installed side by side in the test article

up to the midpoint. The blankets were constructed of polyimide film cover over two layers of 

0.34 pcf fiberglass. 

Twenty wire bundles were fabricated from each selected wire or cable sample using nylon tie 

wraps. Each bundle contained 25 individual 20 AWG wires, except for the riser cable. The riser 

cable (A) bundles contained five individual cables and were close in diameter to the 20 AWG 

wire bundles. All the wires and cables were cut into 92- and 45-inch lengths. Sixteen 92-inchlong bundles were installed in the lengthwise direction using double (duplex) wire bundle clamps. 

Each bundle was approximately 1 inch apart, and each clamp was approximately 4 inches apart.

Six 45-inch-long bundles were installed in the cross (width) direction, again using the doublewire bundle clamps, with the clamps 21 inches apart. This configuration is shown in figure 5. 

Two pieces of Tedlar-faced, 1/4-inch honeycomb ceiling panel, measuring 88 by 85 inches

(total area), were placed side by side in the test article. They were supported by angle iron rails

running lengthwise and across the midsection. 

8
FIGURE 5. TEST ARTICLE CONFIGURATION 

A 9-inch-high by 4-inch-wide by 4-inch-deep polyurethane foam block sitting on a metal peg in a 

small pan was used as the ignition source (see figure 5). Ten milliliters (ml) of heptane (a 

hydrocarbon) was poured on the block, and the block was compressed to distribute the heptane

throughout. An additional 25 ml of heptane was poured in the base of the pan. This is the 

identical ignition source used in the intermediate-scale thermal/acoustic insulation tests that led to

the development of the improved insulation fire test criteria. The top of the block was 1 inch 

below the wire bundle. The block was then ignited (see figure 6). 

FIGURE 6. FOAM BLOCK IGNITION 

9
INTERMEDIATE-SCALE CABIN ATTIC FLAMMABILITY TEST RESULTS.

The first test was a baseline test using only the polyimide blankets. The computer recorded data 

until the foam block fire self-extinguished (see figure 7). The calorimeter is plotted twice in this

graph. The green line is the actual plot of the data points while the black line passing through 

these points is a polynomial moving average for a better depiction of trend. Thermocouple 3, 

located directly above the foam block, reached a temperature of approximately 825°F. The 

calorimeter measured approximately 0.33 Btu/ft2

sec at the 10-minute point of the test, which 

essentially means it did not detect any significant radiant heat. There was no flame propagation 

upon extinguishment of the foam block, demonstrating the fire resistance of the polyimide 

blanket. The charred area was approximately 13 inches long by 10 inches wide. 

FIGURE 7. BASELINE TEMPERATURE AND HEAT FLUX—POLYIMIDE BLANKETS 

Table 4 summarizes the data for the wire and cable bundles tested. 

TABLE 4. INTERMEDIATE-SCALE CABIN ATTIC FLAMMABILITY TEST RESULTS 

Wire Bundle Type 

Flame Propagation 

(upon foam block 

extinguished) 

Burn Area 

(length by width inches) Drippings 

PTFE/polyimide/PTFE No 10 by 9.5 No

Tefzel No 12 by12 No

Spec 2112 No 16 by10.5 No 

Riser cable (A) Yes 27 by 28 Yes 

PVC/nylon Yes Almost completely consumed Yes 

10
It is evident that three types of fire behavior occurred. The first type was exhibited by 

PTFE/polyimide/PTFE, Tefzel and Spec 2112. Each wire bundle had no flame propagation 

upon extinguishment of the foam block ignition source and had relatively small and comparable 

burn areas, although PTFE/polyimide/PTFE had the smallest area. These three wire bundle types 

were good performers. The second fire behavior type was exhibited by riser cable (A) which had 

flame propagation upon extinguishment of the foam block and had drippings (as also was the case 

for PVC/nylon). However, riser cable (A) self-extinguished, although its burn area was 

significantly larger than the good performers, by a factor of 5-8. The third fire behavior type was 

exhibited by PVC/nylon, which was a poor performer with flame spread that practically 

consumed the entire sample. 

The temperatures recorded by thermocouples 3 and 4, shown in figures 8 and 9, sufficiently 

represent the flammability trend of the wires. All the other thermocouples recorded similar 

temperatures (400°F and lower) for all wires tested, with the exception of PVC/nylon. The 

highest temperature recorded for the PTFE/polyimide/PTFE was approximately 750°F. This 

occurred at the start of the test and was recorded by thermocouple 3. The Tefzel peaked at 

825°F approximately 2 minutes into the test, as recorded by thermocouple 4. The Spec 2112 

peaked at approximately 900°F at the start of the test, as detected by thermocouple 3. In figure 8, 

PVC/nylon and riser cable (A) stand out from the good performers. However, in figure 9, riser 

cable (A) is clustered with the good performers because there was no flame propagation 

downward, as clearly occurred for the PVC/nylon. 

0

200

400

600

800

1000

1200

1400

1600

1

305988

117146175204233262291320349378407436465494523552581610639668697726755784813842871900929958987

101610451074110311321161119012191248

Time (Seconds)

Temperature (°F)

PTFE/polyimide/PTFE Tefzel Spec 2112 Riser Cable PVC/nylon

Riser Cable A

PVC/nylon

Tefzel

PTFE/polyimide/PTF

Spec 2112

FIGURE 8. THERMOCOUPLE 3 

11
0

200

400

600

800

1000

1200

1400

1600

1

295785

113141169197225253281309337365393421449477505533561589617645673701729757785813841869897925953981

100910371065109311211149117712051233

Time (Seconds)

Temperature (°F)

PTFE/polyimide/PTFE Tefzel Spec 2112 Riser Cable PVC/nylon

FIGURE 9. THERMOCOUPLE 4 

The heat flux data is shown in figure 10. The Gardon gauge detected less than 0.5 Btu/ft2sec of

radiant heat for all wire bundles, with the exception of PVC/nylon. Even riser cable (A) did not 

burn enough to cause a significant rise in heat flux. 

0.0

0.5

1.0

1.5

2.0

2.5

1

295785

113141169197225253281309337365393421449477505533561589617645673701729757785813841869897925953981

100910371065109311211149117712051233

Time (Seconds)

Heat Flux (BTU/ft2 Sec.)

PTFE/polyimide/PTFE Tefzel Spec 2112 Riser Cable PVC/nylon

FIGURE 10. HEAT FLUX DATA 

12
Figures 11 through 28 show the various stages of the tests. Figures 11-16 show limited and 

comparable upward flame spread for the PTFE/polyimide/PTFE, Tefzel, and Spec 2112 wires. 

The riser cable (A) test is shown in figures 17-21. In addition to the previously noted greater

flame spread, riser cable (A) produced large quantities of smoke. It also shows some sustained 

flaming as the foam block is nearly out (figure 20). The PVC/nylon test is shown in figures 22-

28. The amount of flaming and flame propagation was very extensive for PVC/nylon, and the 

bundles were almost completely consumed (figure 28). All but thermocouple 10 recorded 

temperatures of at least 1000°F. The PVC/nylon test was also very smoky. 

FIGURE 11. IGNITION OF PTFE/POLYIMIDE/PTFE 

FIGURE 12. FLAMEOUT OF PTFE/POLYIMIDE/PTFE 

13
FIGURE 13. IGNITION OF TEFZEL 

FIGURE 14. FLAMEOUT OF TEFZEL 

14
FIGURE 15. IGNITION OF SPEC 2112 

FIGURE 16. FLAMEOUT OF SPEC 2112 

15
FIGURE 17. IGNITION OF RISER CABLE (A) 

FIGURE 18. TEST PROGRESSION OF RISER CABLE (A), VIEW 1 

16
FIGURE 19. TEST PROGRESSION OF RISER CABLE (A), VIEW 2 

FIGURE 20. TEST PROGRESSION OF RISER CABLE (A), VIEW 3 

17
FIGURE 21. FLAMEOUT OF RISER CABLE (A) 

FIGURE 22. IGNITION OF PVC/NYLON 

18
FIGURE 23. TEST PROGRESSION OF PVC/NYLON, VIEW 1 

FIGURE 24. TEST PROGRESSION OF PVC/NYLON, VIEW 2 

19
FIGURE 25. TEST PROGRESSION PVC/NYLON, VIEW 3 

FIGURE 26. TEST PROGRESSION OF PVC/NYLON VIEW 4 

20
FIGURE 27. TEST PROGRESSION OF PVC/NYLON, VIEW 5 

FIGURE 28. FLAMEOUT OF PVC/NYLON TEST 

21
In comparing the intermediate-scale cabin attic flammability test data with the 60° flammability 

test data, there appears to be some correlation in terms of burn length and flame propagation for 

those wires tested. The 60° flammability test burn length and the intermediate-scale cabin attic 

flammability test burn area correlate well for PTFE/polyimide/PTFE, Tefzel, and Spec 2112. 

The PVC/nylon performed poorly, as it did in the 60° flammability test. The riser cable (A) was 

the one exception. While it did eventually self-extinguish in the intermediate-scale cabin attic 

flammability test, significant flame propagation and some drippings were noted. This was

contrary to the 60° flammability test data that showed it passed the requirements of burn length, 

after flame, and drippings, with no after flame or drippings. 

INTERMEDIATE-SCALE CABIN ATTIC FLAMMABILITY TESTS (CONFIGURATION 2). 

To verify the findings from the intermediate-scale cabin attic flammability test, two additional 

tests were run. The PTFE/polyimide/PTFE wire and the riser cable (A) were chosen as the 

samples because the data showed them as being the best and the worst (disregarding PVC/nylon) 

in terms of wiring compliance with the 60° flammability test. Also, the spacing of the bundles 

appeared to have a bearing on the degree of flame propagation. 

In this series of tests, the wire bundle configuration was changed. Instead of intersecting the 

bundles, they were placed in the lengthwise direction only. Thirty bundles, each 42 inches long,

were installed in the duplex wire bundle clamps. The distance from center to center of the clamps 

was 3 inches and each wire bundle was 1 inch apart. Also, the test area was halved. Figure 29 

shows the orientation of the wire bundles. 

FIGURE 29. INTERMEDIATE-SCALE CABIN ATTIC FLAMMABILITY TESTS 

CONFIGURATION 2 

22
INTERMEDIATE-SCALE CABIN ATTIC FLAMMABILITY TEST RESULTS

(CONFIGURATION 2). 

Figures 30 and 31 show the temperature and heat flux profiles of PTFE/polyimide/PTFE and riser 

cable (A). All thermocouples are shown for these two tests. 

0

200

400

600

800

1000

1200

1400

1600

1

1223344556677889

100111

122133144155166177188199210221232243254265276287298309320331342353364375386397408419430

Time (Seconds)

Temperature (°F)

0.00

0.50

1.00

1.50

2.00

2.50

Heat Flux - BTU/FT2 Second

Center Top Center Top Mid Center Btm Mid Center Btm Right Top Right Mid

Right Btm Left Top Left Mid Left Btm Calorimeter Poly. (Calorimeter)

FIGURE 30. PTFE/POLYIMIDE/PTFE TEMPERATURE AND HEAT FLUX PROFILE 

0

200

400

600

800

1000

1200

1400

1600

1

14274053667992

105118131144157170183196209222235248261274287300313326339352365378391404417430443456469482495508521534547560

Time (Seconds)

Degrees Farenheit

0

0.5

1

1.5

2

2.5

Heat Flux (BTUs/ft

2 Sec.)

Center Top Center Top Mid Center Btm Mid Center Btm Right Top Right Mid

Right Btm Left Top Left Mid Left Btm Calorimeter Poly. (Calorimeter)

FIGURE 31. RISER CABLE (A) TEMPERATURE AND HEAT FLUX PROFILE 

23
The temperature of the PTFE/polyimide/PTFE rose to approximately 1100°F, as detected by

thermocouple 3, and then dropped. Ninety seconds into the test, the temperature spiked again, 

and then decreased until the foam block was consumed. There was approximately 9 inches of 

burn length in the lengthwise direction and 7 inches in the cross direction. No flame propagation 

occurred after the foam block extinguished, nor were there any drippings. Figures 32 through 35 

show the ignition, progression, and flameout of the test. Again, the PTFE/polyimide/PTFE was

an excellent performer, and the burn area was similar to that exhibited in the first intermediatescale cabin attic flammability test configuration. 

By contrast, the riser cable (A) was almost completely consumed, indicating a strong dependence

on the wiring configuration. The smoke became very dense so quickly that the test personnel 

were forced to exit the test area. This occurred approximately 3 minutes into the test. The 

bundles that were unburned were below the foam block and at the ends of the bundles at the far 

end of the test article. From figure 31, the temperature profile of all but the lower thermocouples 

indicate the flame spread. A maximum temperature of approximately 1300°F was recorded by 

thermocouple 5 about 6 minutes into the test, and the Gardon gauge detected approximately 2 

Btu/ft2 sec of radiant heat at that time. Figures 36 through 42 show the ignition and flame 

progression during various stages of the burn. The flame out of the riser cable (A) is shown in 

two directions in figures 43 and 44. The thermal degradation of the riser cable (A) is very 

extensive (figures 43 and 44). Figures 38 through 42 were not actual photos but were taken from 

the videotape that continued to record after the personnel evacuated the test area. 

FIGURE 32. IGNITION OF PTFE/POLYIMIDE/PTFE 

24
FIGURE 33. TEST PROGRESSION OF PTFE/POLYIMIDE/PTFE, VIEW 1 

FIGURE 34. TEST PROGRESSION PTFE/POLYIMIDE/PTFE, VIEW 2 

25
FIGURE 35. FLAMEOUT OF PTFE/POLYIMIDE/PTFE 

FIGURE 36. IGNITION OF RISER CABLE (A) 

26
FIGURE 37. TEST PROGRESSION OF RISER CABLE (A), VIEW 1 

FIGURE 38. TEST PROGRESSION OF RISER CABLE (A), VIEW 2 

27
FIGURE 39. TEST PROGRESSION OF RISER CABLE (A), VIEW 3 

FIGURE 40. TEST PROGRESSION OF RISER CABLE (A), VIEW 4 

28
FIGURE 41. TEST PROGRESSION OF RISER CABLE (A), VIEW 5 

FIGURE 42. TEST PROGRESSION OF RISER CABLE (A), VIEW 6 

29
FIGURE 43. FLAMEOUT OF RISER CABLE (A), CROSS VIEW

FIGURE 44. FLAMEOUT OF RISER CABLE (A), LENGTHWISE VIEW

30
CONCLUSIONS

The 60° single wire flammability test may not be adequate to qualify wire when bundled and

subjected to a severe ignition source. 

Certain types of aircraft wiring, particularly PTFE/polyimide/PTFE, exhibit a high degree of fire 

resistance when subjected to a severe ignition source. The degree of fire resistance appeared to

be independent of wiring configuration (spacing) in the intermediate-scale cabin attic

flammability test.

The flammability of the riser cable (A) was dependent on the wiring configuration during the 

intermediate-scale cabin attic flammability tests.

Although some correlation existed between the 60° flammability test and the intermediate-scale

cabin attic flammability tests, it appeared to be limited to the most fire-resistant samples that 

easily passed the 60° flammability test. No correlation exists for materials that have greater burn 

lengths or marginally passed the test. 

The most flammable wiring sample tested was PVC/nylon. 

REFERENCES

1. Cahill, P., “Evaluation of Fire Test Methods for Aircraft Thermal Acoustical Insulation,” 

FAA Report DOT/FAA/AR-97/58, September 1997. 

2. Marker, T., “Development of Improved Flammability Criteria for Aircraft Thermal 

Acoustic Insulation,” FAA Report DOT/FAA/AR-99/44, September 2000. 

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