MIL-W-22759 Vertical Flammability 

Test Versus the 60 Degree 

Flammability Test 

Cesar Gomez 

June 2004 

DOT/FAA/AR-TN04/21 

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-TN04/21

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

4. Title and Subtitle

MIL-W-22759 VERTICAL FLAMMABILITY TEST VERSUS THE 60 DEGREE 

5. Report Date

June 2004

FLAMMABILITY TEST 6. Performing Organization Code

7. Author(s)

Cesar A. Gomez 

8. Performing Organization Report No.

9. Performing Organization Name and Address

Federal Aviation Administration

William J. Hughes Technical Center 

Airport and Aircraft Safety Research and Development 

10. Work Unit No. (TRAIS)

Airworthiness Assurance 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-111

15. Supplementary Notes

16. Abstract

There is a need to clarify the wire flammability compliance requirements specified in the latest amendments of Title 14 Code of

Federal Regulations and the Airworthiness Manual (CFR/AWM) for the detailed specification sheet MIL-W-22759/16. CFR

requirements prescribe a 60 degree flammability test for the MIL-W-22759 specification sheet, while MIL-W-22759/16 calls for a 

vertical flammability test. Confusion lies as to which of the requirements should be followed. This technical note will show how 

the MIL-W-22759/16 specification sheet satisfies both flammability requirements. 

17. Key Words

MIL-W-22759, MIL-W-22759/16, Vertical flammability test,

60 degree flammability test

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

46 

22. Price

Form DOT F1700.7 (8-72) Reproduction of completed page authorized
TABLE OF CONTENTS 

Page 

INTRODUCTION 1

TEST METHOD 2 

The 60 Degree Flame Test 2 

The Vertical Flame Test 2 

Apparatus 2

Procedure 3

RESULTS 3 

CONCLUSION 4

APPENDICES 

A—14 CFR Part 23

B—14 CFR Part 25

C—14 CFR Parts 27 and 29

D—Flammability, Smoke, and Dry Arc Tracking Tests of Aircraft Electrical Wire

 Insulations

LIST OF TABLES 

Table Page 

1 The 60 Degree Flammability Test Results 4 

2 Vertical Flammability Test Results 4 

iii/iv
INTRODUCTION

There is a need to clarify wire flammability compliance requirements specified in the latest

amendments of Title 14 Code of Federal Regulations and the Airworthiness Manual 

((CFR/AWM) for the detailed specification sheets in MIL-W-22759/16, specifically 14 CFR 

23.1359, 25.869, 27.1365, and 29.1359. The detailed specification sheets for MIL-W-22759/16 

call out a different flammability test methodology and pass or fail criteria than those specified by

the CFR/AWM requirements. In general, the Federal Aviation Administration (FAA) accepts

MIL standard tests as acceptable equivalents to FAA requirements where these standards meet or 

exceed FAA requirements. This Technical Note provides a comparison of flammability test

results on MIL-W-22759/16 wire using both FAA and MIL-W test methodologies. The text 

shown in bold type emphasizes the parts related to flammability in each of the CFRs in question. 

The Airworthiness Standards of electrical systems and equipment for normal, utility, acrobatic,

and commuter category airplanes 14 CFR 23.1359 states (a) each component of the electrical 

system must meet the applicable fire protection requirements of §§23.863 and 23.1182 (see 

appendix A of this report). (b) Electrical cables, terminals, and equipment in designated fire 

zones that are used during emergency procedures must be fire-resistant. (c) Insulation on 

electrical wire and electrical cable must be self-extinguishing when tested at an angle of 60 

degrees in accordance with the applicable portions of appendix F of this part (see appendix 

A of this report), or other approved equivalent methods. The average burn length must not 

exceed 3 inches (76 mm) and the average flame time after removal of the flame source must not

exceed 30 seconds. Drippings from the test specimen must not continue to flame for more than

an average of 3 seconds after falling. 

The Airworthiness Standards for fire protection of systems for transport category airplanes 14 

CFR 25.869 states (a) Electrical system components: 

(1) Components of the electrical system must meet the applicable fire and smoke 

protection requirements of §§25.831(c) and 25.863 (see appendix B of this report). 

(2) Electrical cables, terminals, and equipment in designated fire zones, that are used 

during emergency procedures, must be at least fire resistant. 

(3) Main power cables (including generator cables) in the fuselage must be designed to 

allow a reasonable degree of deformation and stretching without failure and must be (i) 

Isolated from flammable fluid lines; or (ii) Shrouded by means of electrically insulated, 

flexible conduit, or equivalent, which is in addition to the normal cable insulation. 

(4) Insulation on electrical wire and electrical cable installed in any area of the

fuselage must be self-extinguishing when tested in accordance with the applicable 

portions of part I, appendix F of this part (see appendix B of this report). 

The Airworthiness Standards of electrical systems and equipment, specifically electric cables for 

normal category rotorcraft 14 CFR 27.1365 states (a) each electric connecting cable must be of 

adequate capacity. (b) Each cable that would overheat in the event of circuit overload or fault 

must be at least flame resistant and may not emit dangerous quantities of toxic fumes. (c) 

Insulation on electrical wire and cable installed in the rotorcraft must be self-extinguishing

1
when tested in accordance with Appendix F, Part I (a)(3), of part 25 of this chapter (see 

appendix B of this report). 

The Airworthiness Standards of electrical systems and equipment for the protection of fire and 

smoke of transport category rotorcraft 14 CFR 29.1359 states (a) Components of the electrical 

system must meet the applicable fire and smoke protection provisions of §§29.831 and 29.863 

(see appendix C of this report). (b) Electrical cables, terminals, and equipment, in designated 

fire zones, and that are used in emergency procedures, must be at least fire resistant. (c) 

Insulation on electrical wire and cable installed in the rotorcraft must be self-extinguishing

when tested in accordance with Appendix F, Part I (a)(3), of part 25 of this chapter (see 

appendix B of this report). 

TEST METHOD

THE 60 DEGREE FLAME TEST. 

The 60 degree test as written in Appendix F, Part I (a)(3) test procedures states that a minimum 

of three specimens of each wire specification (make and size) must be tested. The specimen of 

wire or cable (including insulation) must be placed at an angle of 60-degrees with the horizontal

in the cabinet specified in subparagraph (3) of this paragraph with the cabinet door open during 

the test, or must be placed within a chamber approximately 2 feet high by 1 foot by 1 foot, open 

at the top and at one vertical side (front), and which allows sufficient flow of air for complete 

combustion, but which is free from drafts. The specimen must be parallel to and approximately 

6 inches from the front of the chamber. The lower end of the specimen must be held rigidly 

clamped. The upper end of the specimen must pass over a pulley or rod and must have an 

appropriate weight attached to it so that the specimen is held tautly throughout the flammability

test. The test specimen span between lower clamp and upper pulley or rod must be 24 inches 

and must be marked 8 inches from the lower end to indicate the central point for flame

application. A flame from a Bunsen or Tirrill burner must be applied for 30 seconds at the test

mark. The burner must be mounted underneath the test mark on the specimen, perpendicular to 

the specimen and at an angle of 30-degrees to the vertical plane of the specimen. The burner 

must have a nominal bore of 3/8-inch and be adjusted to provide a 3-inch high flame with an 

inner cone approximately one-third of the flame height. The minimum temperature of the hottest 

portion of the flame, as measured with a calibrated thermocouple pyrometer, may not be less 

than 1750°F. The burner must be positioned so that the hottest portion of the flame is applied to

the test mark on the wire. Flame time, burn length, and flaming time of drippings, if any, must

be recorded. The burn length determined in accordance with paragraph (8) of this paragraph 

must be measured to the nearest tenth of an inch. Breaking of the wire specimens is not 

considered a failure. 

THE VERTICAL FLAME TEST. 

APPARATUS. The flammability test chamber shall be approximately 1 foot square by 2 feet in

height and shall be open at the top and front to provide adequate ventilation for combustion but 

prevent drafts. Inside the chamber, near the open top, a clamp shall be provided from which the 

wire specimen may be suspended vertically about 6 inches in front of the rear wall of the

2
chamber and equidistant from the two sides. The test burner shall be a Bunsen type gas burner 

having a 1/4-inch inlet, a bore of 3/8 inch nominal, and a length of approximately 4 inches above 

the primary air inlets. The burner shall be capable of providing the specified test flame, which 

shall be a 3-inch flame with an inner core approximately one-third of total flame height and a 

temperature, at its hottest portion, of 1010° ±56°C (1850° ±100°F), as measured by a 

thermocouple pyrometer. 

PROCEDURE. An 18 ±1/2-inch wire specimen, marked 14 ±1/2 inches from its upper end to

indicate where the test flame is to be applied, shall be suspended in the vertical position in the

chamber and a weight equal to that specified for life cycle test of the same wire shall be attached

to the lower end of the specimen to keep it taut during the flame exposure. With the test flame 

adjusted as specified in the preceding paragraph and with the burner held upright but inclined 20 

degrees from the vertical toward the specimen, the hottest portion of the flame shall be applied 

for 15 seconds to the approximate position of the test mark on the wire and shall then be 

withdrawn. The duration of flaming in the specimen after withdrawal of the gas test flame shall 

be timed and recorded in seconds. The burn length on the specimen as indicated by burned, 

charred, or melted insulation shall be measured and recorded to the nearest 1/8 inch. Areas of

the specimen having the original insulation undamaged but covered with soot deposit removable 

by wiping or covered with material which has melted and flowed down the wire shall no be 

considered as part of the burn length. Breaking of the wire specimen in size 24 or smaller shall 

not be considered as a failure. If breaking occurs in three or more specimens, a 22-gage

specimen may be substituted for purpose of this test. 

RESULTS

Industry experts state that the vertical flammability test, as specified in the MIL-W-22759/16

sheet, is more stringent than the tests used in the base MIL-W-22759 specification, the SAE

AS4373, or in the CFR, which all require the 60 degree flame test with minor variations. To test

this theory, the FAA conducted an experiment using both flammability tests; two random 

M22759/16 wires were chosen and tested using the vertical and 60 degree flame tests. The wires 

were of two gauge sizes (18 and 22 AWG) and from two manufacturers. Acknowledgement is

given that different manufacturers of this type of wire may produce wire with different 

construction and physical properties. The designer or engineer must show compliance to the 

specification when choosing this type of wire for an application. The 60 degree flammability test

was done per the SAE AS4373 test method, and the vertical flammability test was done per MILW-22759/16. 

The 14 CFR Part 25 Appendix F Part I (3) electrical system components for transport category 

airplanes states that insulation on electrical wire or cable installed in any area of the fuselage 

must be self-extinguishing when subjected to the 60 degree test specified in part I of this 

appendix. The average burn length may not exceed 3 inches, and the average flame time after

removal of the 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. A sheet of facial 

tissue, conforming to A-A-1505, is used to test the after-flame of the specimen per SAE AS4373 

Method 801, Flammability. 

3
Table 1 shows that the MIL-22759/16 wire passed the 60 degree flammability test, according to 

the CFR requirements. 

TABLE 1. THE 60 DEGREE FLAMMABILITY TEST RESULTS 

Sample 

Time of Flame 

Application

(sec.) 

Duration of 

After-Flame

(sec.) 

Travel of 

Flame 

(in.) 

Flaming 

Drops 

(y/n) 

Tissue 

Ignites 

(y/n) 

Result 

(Pass/Fail)

M22759/16-18 30 0.1 2 N N P

M22759/16-22 30 0.2 2 N N P

MIL-W-22759/16 specification sheets prescribe a vertical flame test where the pass criteria for 

these wire types include a 2-inch (maximum) after-flame, 5.5-inch (maximum) burn length, and 

no post dielectric test. 

Table 2 shows that the MIL-22759/16 wire passed the vertical flammability test, according to its

specification sheet. 

TABLE 2. VERTICAL FLAMMABILITY TEST RESULTS 

Sample 

Time of Flame 

Application

(sec.) 

Duration of 

After-Flame

(sec.) 

Travel of 

Flame 

(in.) 

Flaming 

Drops 

(y/n) 

Tissue 

Ignites 

(y/n) 

Result 

(Pass/Fail) 

M22759/16-18 15 0.2 4.375 N N P

M22759/16-22 15 0.2 3.5 N N P

Patricia Cahill, in support of the Fire Safety Branch at the FAA William J. Hughes Technical 

Center, has been performing wire flammability tests in accordance with the applicable portions 

of Part I, Appendix F of 14 CFR 25.869 since 1987. Wire under MIL-W-22759/16 have been 

included in these tests and have been tested numerous times. As expected, different 

manufacturing lots and dates come into play. One of the earliest reports, DOT/FAA/CT-89/21, 

“Flammability, Smoke, and Dry Arc Tracking Tests of Aircraft Electrical Wire Insulations,”

evaluated the flammability of MIL-W-22759/16 (see appendix D of this report). The average 

burn length was found to be 2 inches with no after-flame or drippings. The most recent 60

degree flammability test of this insulation was conducted in 2003, and an average burn length of 

2 inches with no after-flame or drippings was found. A report has not yet been issued for the 

2003 testing. 

CONCLUSION

The Aging Electrical Systems Research Program at the FAA William J. Hughes Technical 

Center conducted experiments comparing both flammability requirements (60 degree test versus

vertical test) using a sample of wires chosen at random from different manufacturers. For the 

MIL-W-22759/16 wires tested, if the wire passed the MIL spec test, then it also passed the

4
FAA’s pass/fail criteria. The results from these experiments support the theory that flammability 

testing per the MIL-W-22759/16 standard is sufficient to satisfy FAA flammability requirements

prescribed in the CFR (14 CFR 23.1359, 25.869, 27.1365, and 29.1359) for the wire samples 

tested. Finally, these results are consistent with previous tests done at the FAA William J. 

Hughes Technical Center on MIL-W-22759/16 wire, which showed that this wire construction 

passes the FAA 60 degree burn requirements. 

5/6
APPENDIX A—14 CFR PART 23

§ 23.863 Flammable fluid fire protection 

(a) In each area where flammable fluids or vapors might escape by leakage of a fluid system, 

there must be means to minimize the probability of ignition of the fluids and vapors, and the

resultant hazard if ignition does occur. 

(b) Compliance with paragraph (a) of this section must be shown by analysis or tests, and the 

following factors must be considered: 

(1) Possible sources and paths of fluid leakage, and means of detecting leakage. 

(2) Flammability characteristics of fluids, including effects of any combustible or 

absorbing materials. 

(3) Possible ignition sources, including electrical faults, overheating of equipment, and 

malfunctioning of protective devices. 

(4) Means available for controlling or extinguishing a fire, such as stopping flow of 

fluids, shutting down equipment, fireproof containment, or use of extinguishing agents. 

(5) Ability of airplane components that are critical to safety of flight to withstand fire and 

heat. 

(c) If action by the flight crew is required to prevent or counteract a fluid fire (e.g. equipment

shutdown or actuation of a fire extinguisher), quick acting means must be provided to alert the 

crew. 

(d) Each area where flammable fluids or vapors might escape by leakage of a fluid system must

be identified and defined. 

§ 23.1182 Nacelle areas behind firewalls 

Components, lines, and fittings, except those subject to the provisions of §23.1351(e), located 

behind the engine-compartment firewall must be constructed of such materials and located at 

such distances from the firewall that they will not suffer damage sufficient to endanger the 

airplane if a portion of the engine side of the firewall is subjected to a flame temperature of not 

less than 2000 °F for 15 minutes. 

Appendix F to Part 23—Test Procedure 

Acceptable test procedure for self-extinguishing materials for showing compliance with 

§§23.853, 23.855 and 23.1359 

(a) Conditioning. Specimens must be conditioned to 70 degrees F, plus or minus 5 degrees, and 

at 50 percent plus or minus 5 percent relative humidity until moisture equilibrium is reached or 

for 24 hours. Only one specimen at a time may be removed from the conditioning environment 

immediately before subjecting it to the flame. 

A-1
(b) Specimen configuration. Except as provided for materials used in electrical wire and cable

insulation and in small parts, materials must be tested either as a section cut from a fabricated 

part as installed in the airplane or as a specimen simulating a cut section, such as: a specimen cut 

from a flat sheet of the material or a model of the fabricated part. The specimen may be cut from

any location in a fabricated part; however, fabricated units, such as sandwich panels, may not be

separated for a test. The specimen thickness must be no thicker than the minimum thickness to 

be qualified for use in the airplane, except that: (1) Thick foam parts, such as seat cushions, 

must be tested in 1/2 inch thickness; (2) when showing compliance with §23.853(d)(3)(v) for 

materials used in small parts that must be tested, the materials must be tested in no more than 1/8 

inch thickness; (3) when showing compliance with §23.1359(c) for materials used in electrical 

wire and cable insulation, the wire and cable specimens must be the same size as used in the

airplane. In the case of fabrics, both the warp and fill direction of the weave must be tested to

determine the most critical flammability conditions. When performing the tests prescribed in 

paragraphs (d) and (e) of this appendix, the specimen must be mounted in a metal frame so that 

(1) in the vertical tests of paragraph (d) of this appendix, the two long edges and the upper edge 

are held securely; (2) in the horizontal test of paragraph (e) of this appendix, the two long edges 

and the edge away from the flame are held securely; (3) the exposed area of the specimen is at 

least 2 inches wide and 12 inches long, unless the actual size used in the airplane is smaller; and 

(4) the edge to which the burner flame is applied must not consist of the finished or protected 

edge of the specimen but must be representative of the actual cross section of the material or part 

installed in the airplane. When performing the test prescribed in paragraph (f) of this appendix, 

the specimen must be mounted in metal frame so that all four edges are held securely and the 

exposed area of the specimen is at least 8 inches by 8 inches. 

(c) Apparatus. Except as provided in paragraph (g) of this appendix, tests must be conducted in 

a draft-free cabinet in accordance with Federal Test Method Standard 191 Method 5903 (revised 

Method 5902) which is available from the General Services Administration, Business Service 

Center, Region 3, Seventh and D Streets SW., Washington, D.C. 20407, or with some other 

approved equivalent method. Specimens that are too large for the cabinet must be tested in 

similar draft-free conditions. 

(d) Vertical test. A minimum of three specimens must be tested and the results averaged. For 

fabrics, the direction of weave corresponding to the most critical flammability conditions must 

be parallel to the longest dimension. Each specimen must be supported vertically. The specimen 

must be exposed to a Bunsen or Tirrill burner with a nominal 3/8-inch I.D. tube adjusted to give 

a flame of 1 1/2 inches in height. The minimum flame temperature measured by a calibrated 

thermocouple pryometer in the center of the flame must be 1550 °F. The lower edge of the

specimen must be three-fourths inch above the top edge of the burner. The flame must be

applied to the centerline of the lower edge of the specimen. For materials covered by 

§§23.853(d)(3)(i) and 23.853(f), the flame must be applied for 60 seconds and then removed. 

For materials covered by §23.853(d)(3)(ii), the flame must be applied for 12 seconds and then 

removed. Flame time, burn length, and flaming time of drippings, if any, must be recorded. The

burn length determined in accordance with paragraph (h) of this appendix must be measured to 

the nearest one-tenth inch. 

A-2
(e) Horizontal test. A minimum of three specimens must be tested and the results averaged. 

Each specimen must be supported horizontally. The exposed surface when installed in the

airplane must be face down for the test. The specimen must be exposed to a Bunsen burner or 

Tirrill burner with a nominal 3/8-inch I.D. tube adjusted to give a flame of 1 1/2 inches in height. 

The minimum flame temperature measured by a calibrated thermocouple pyrometer in the center 

of the flame must be 1550 °F. The specimen must be positioned so that the edge being tested is 

three-fourths of an inch above the top of, and on the centerline of, the burner. The flame must be

applied for 15 seconds and then removed. A minimum of 10 inches of the specimen must be 

used for timing purposes, approximately 1 1/2 inches must burn before the burning front reaches 

the timing zone, and the average burn rate must be recorded. 

(f) Forty-five degree test. A minimum of three specimens must be tested and the results 

averaged. The specimens must be supported at an angle of 45 degrees to a horizontal surface. 

The exposed surface when installed in the aircraft must be face down for the test. The specimens

must be exposed to a Bunsen or Tirrill burner with a nominal 3/8 inch I.D. tube adjusted to give 

a flame of 1 1/2 inches in height. The minimum flame temperature measured by a calibrated 

thermocouple pyrometer in the center of the flame must be 1550°F. Suitable precautions must be 

taken to avoid drafts. The flame must be applied for 30 seconds with one-third contacting the 

material at the center of the specimen and then removed. Flame time, glow time, and whether 

the flame penetrates (passes through) the specimen must be recorded. 

(g) Sixty-degree test. A minimum of three specimens of each wire specification (make and size) 

must be tested. The specimen of wire or cable (including insulation) must be placed at an angle 

of 60 degrees with the horizontal in the cabinet specified in paragraph (c) of this appendix, with 

the cabinet door open during the test or placed within a chamber approximately 2 feet high × 1 

foot × 1 foot, open at the top and at one vertical side (front), that allows sufficient flow of air for 

complete combustion but is free from drafts. The specimen must be parallel to and 

approximately 6 inches from the front of the chamber. The lower end of the specimen must be 

held rigidly clamped. The upper end of the specimen must pass over a pulley or rod and must

have an appropriate weight attached to it so that the specimen is held tautly throughout the 

flammability test. The test specimen span between lower clamp and upper pulley or rod must be 

24 inches and must be marked 8 inches from the lower end to indicate the central point for flame 

application. A flame from a Bunsen or Tirrill burner must be applied for 30 seconds at the test

mark. The burner must be mounted underneath the test mark on the specimen, perpendicular to 

the specimen and at an angle of 30 degrees to the vertical plane of the specimen. The burner 

must have a nominal bore of three-eighths inch, and must be adjusted to provide a three-inchhigh flame with an inner cone approximately one-third of the flame height. The minimum 

temperature of the hottest portion of the flame, as measured with a calibrated thermocouple

pyrometer, may not be less than 1,750 °F. The burner must be positioned so that the hottest

portion of the flame is applied to the test mark on the wire. Flame time, burn length, and flaming 

time drippings, if any, must be recorded. The burn length determined in accordance with

paragraph (h) of this appendix must be measured to the nearest one-tenth inch. Breaking of the 

wire specimen is not considered a failure. 

(h) Burn length. Burn length is the distance from the original edge to the CFRthest evidence of

damage to the test specimen due to flame impingement, including areas of partial or complete 

A-3
consumption, charring, or embrittlement, but not including areas sooted, stained, warped, or 

discolored, nor areas where material has shrunk or melted away from the heat source. 

A-4
APPENDIX B—14 CFR PART 25

§ 25.831 Ventilation 

(a) Under normal operating conditions and in the event of any probable failure conditions of any 

system, which would adversely affect the ventilating air, the ventilation system must be designed

to provide a sufficient amount of uncontaminated air to enable the crewmembers to perform their 

duties without undue discomfort or fatigue and to provide reasonable passenger comfort. For

normal operating conditions, the ventilation system must be designed to provide each occupant 

with an airflow containing at least 0.55 pounds of fresh air per minute. 

(b) Crew and passenger compartment air must be free from harmful or hazardous concentrations 

of gases or vapors. In meeting this requirement, the following apply: 

(1) Carbon monoxide concentrations in excess of 1 part in 20,000 parts of air are 

considered hazardous. For test purposes, any acceptable carbon monoxide detection

method may be used. 

(2) Carbon dioxide concentration during flight must be shown not to exceed 0.5 percent 

by volume (sea level equivalent) in compartments normally occupied by passengers or 

crewmembers. 

(c) There must be provisions made to ensure that the conditions prescribed in paragraph (b) of 

this section are met after reasonably probable failures or malfunctioning of the ventilating, 

heating, pressurization, or other systems and equipment. 

(d) If accumulation of hazardous quantities of smoke in the cockpit area is reasonably probable, 

smoke evacuation must be readily accomplished, starting with full pressurization and without 

depressurizing beyond safe limits. 

(e) Except as provided in paragraph (f) of this section, means must be provided to enable the 

occupants of the following compartments and areas to control the temperature and quantity of

ventilating air supplied to their compartment or area independently of the temperature and 

quantity of air supplied to other compartments and areas: 

(1) The flight crew compartment. 

(2) Crewmember compartments and areas other than the flight crew compartment unless

the crewmember compartment or area is ventilated by air interchange with other 

compartments or areas under all operating conditions. 

(f) Means to enable the flight crew to control the temperature and quantity of ventilating air

supplied to the flight crew compartment independently of the temperature and quantity of 

ventilating air supplied to other compartments are not required if all of the following conditions

are met: 

(1) The total volume of the flight crew and passenger compartments is 800 cubic feet or 

less. 

(2) The air inlets and passages for air to flow between flight crew and passenger 

compartments are arranged to provide compartment temperatures within 5 degrees F. of 

each other and adequate ventilation to occupants in both compartments. 

B-1
(3) The temperature and ventilation controls are accessible to the flight crew. 

(g) The exposure time at any given temperature must not exceed the values shown in the 

following graph after any improbable failure condition. 

 

§ 25.863 Flammable fluid fire protection 

(a) In each area where flammable fluids or vapors might escape by leakage of a fluid system, 

there must be means to minimize the probability of ignition of the fluids and vapors, and the

resultant hazards if ignition does occur. 

(b) Compliance with paragraph (a) of this section must be shown by analysis or tests, and the 

following factors must be considered: 

(1) Possible sources and paths of fluid leakage, and means of detecting leakage. 

(2) Flammability characteristics of fluids, including effects of any combustible or 

absorbing materials. 

(3) Possible ignition sources, including electrical faults, overheating of equipment, and 

malfunctioning of protective devices. 

(4) Means available for controlling or extinguishing a fire, such as stopping flow of 

fluids, shutting down equipment, fireproof containment, or use of extinguishing agents. 

(5) Ability of airplane components that are critical to safety of flight to withstand fire and 

heat. 

(c) If action by the flight crew is required to prevent or counteract a fluid fire (e.g., equipment 

shutdown or actuation of a fire extinguisher) quick acting means must be provided to alert the 

crew. 

(d) Each area where flammable fluids or vapors might escape by leakage of a fluid system must

be identified and defined. 

B-2
Appendix F to Part 25 

Part I—Test Criteria and Procedures for Showing Compliance with §25.853, or §25.855 

(a) Material test criteria 

(1) Interior compartments occupied by crew or passengers. 

(i) Interior ceiling panels, interior wall panels, partitions, galley structure, large cabinet 

walls, structural flooring, and materials used in the construction of stowage 

compartments (other than underseat stowage compartments and compartments for

stowing small items such as magazines and maps) must be self-extinguishing when tested 

vertically in accordance with the applicable portions of part I of this appendix. The 

average burn length may not exceed 6 inches and the average flame time after removal of 

the flame source may not exceed 15 seconds. Drippings from the test specimen may not

continue to flame for more than an average of 3 seconds after falling. 

(ii) Floor covering, textiles (including draperies and upholstery), seat cushions, padding, 

decorative and nondecorative coated fabrics, leather, trays and galley furnishings, 

electrical conduit, air ducting, joint and edge covering, liners of Class B and E cargo or

baggage compartments, floor panels of Class B, C, D, or E cargo or baggage 

compartments, cargo covers and transparencies, molded and thermoformed parts, air 

ducting joints, and trim strips (decorative and chafing), that are constructed of materials 

not covered in subparagraph (iv) below, must be self-extinguishing when tested vertically 

in accordance with the applicable portions of part I of this appendix or other approved

equivalent means. The average burn length may not exceed 8 inches, and the average

flame time after removal of the flame source may not exceed 15 seconds. Drippings from

the test specimen may not continue to flame for more than an average of 5 seconds after 

falling. 

(iii) Motion picture film must be safety film meeting the Standard Specifications for 

Safety Photographic Film PHI.25 (available from the American National Standards 

Institute, 1430 Broadway, New York, NY 10018). If the film travels through ducts, the 

ducts must meet the requirements of subparagraph (ii) of this paragraph. 

(iv) Clear plastic windows and signs, parts constructed in whole or in part of elastomeric 

materials, edge lighted instrument assemblies consisting of two or more instruments in a

common housing, seat belts, shoulder harnesses, and cargo and baggage tiedown 

equipment, including containers, bins, pallets, etc., used in passenger or crew 

compartments, may not have an average burn rate greater than 2.5 inches per minute 

when tested horizontally in accordance with the applicable portions of this appendix. 

(v) Except for small parts (such as knobs, handles, rollers, fasteners, clips, grommets, rub 

strips, pulleys, and small electrical parts) that would not contribute significantly to the

propagation of a fire and for electrical wire and cable insulation, materials in items not 

specified in paragraphs (a)(1)(i), (ii), (iii), or (iv) of part I of this appendix may not have a 

burn rate greater than 4.0 inches per minute when tested horizontally in accordance with 

the applicable portions of this appendix. 

B-3
(2) Cargo and baggage compartments not occupied by crew or passengers. 

(i) [Reserved] 

(ii) A cargo or baggage compartment defined in §25.857 as Class B or E must have a

liner constructed of materials that meet the requirements of paragraph (a)(1)(ii) of part I 

of this appendix and separated from the airplane structure (except for attachments). In 

addition, such liners must be subjected to the 45-degree angle test. The flame may not 

penetrate (pass through) the material during application of the flame or subsequent to its 

removal. The average flame time after removal of the flame source may not exceed 15

seconds, and the average glow time may not exceed 10 seconds. 

(iii) A cargo or baggage compartment defined in §25.857 as Class B, C, D, or E must

have floor panels constructed of materials which meet the requirements of paragraph 

(a)(1)(ii) of part I of this appendix and which are separated from the airplane structure 

(except for attachments). Such panels must be subjected to the 45-degree angle test. The 

flame may not penetrate (pass through) the material during application of the flame or 

subsequent to its removal. The average flame time after removal of the flame source may 

not exceed 15 seconds, and the average glow time may not exceed 10 seconds. 

(iv) Insulation blankets and covers used to protect cargo must be constructed of materials 

that meet the requirements of paragraph (a)(1)(ii) of part I of this appendix. Tiedown 

equipment (including containers, bins, and pallets) used in each cargo and baggage 

compartment must be constructed of materials that meet the requirements of paragraph 

(a)(1)(v) of part I of this appendix. 

(3) Electrical system components. Insulation on electrical wire or cable installed in any area of 

the fuselage must be self-extinguishing when subjected to the 60 degree test specified in part I of 

this appendix. The average burn length may not exceed 3 inches, and the average flame time 

after removal of the 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. 

(b) Test Procedures 

(1) Conditioning. Specimens must be conditioned to 70±5 F., and at 50 percent ±5 percent 

relative humidity until moisture equilibrium is reached or for 24 hours. Each specimen must 

remain in the conditioning environment until it is subjected to the flame. 

(2) Specimen configuration. Except for small parts and electrical wire and cable insulation, 

materials must be tested either as section cut from a fabricated part as installed in the airplane or

as a specimen simulating a cut section, such as a specimen cut from a flat sheet of the material or 

a model of the fabricated part. The specimen may be cut from any location in a fabricated part; 

however, fabricated units, such as sandwich panels, may not be separated for test. Except as

noted below, the specimen thickness must be no thicker than the minimum thickness to be

qualified for use in the airplane. Test specimens of thick foam parts, such as seat cushions, must

be 1/2-inch in thickness. Test specimens of materials that must meet the requirements of 

paragraph (a)(1)(v) of part I of this appendix must be no more than 1/8-inch in thickness.

Electrical wire and cable specimens must be the same size as used in the airplane. In the case of

fabrics, both the warp and fill direction of the weave must be tested to determine the most critical 

flammability condition. Specimens must be mounted in a metal frame so that the two long edges

and the upper edge are held securely during the vertical test prescribed in subparagraph (4) of 

B-4
this paragraph and the two long edges and the edge away from the flame are held securely during 

the horizontal test prescribed in subparagraph (5) of this paragraph. The exposed area of the 

specimen must be at least 2 inches wide and 12 inches long, unless the actual size used in the

airplane is smaller. The edge to which the burner flame is applied must not consist of the 

finished or protected edge of the specimen but must be representative of the actual cross-section 

of the material or part as installed in the airplane. The specimen must be mounted in a metal

frame so that all four edges are held securely and the exposed area of the specimen is at least 8 

inches by 8 inches during the 45° test prescribed in subparagraph (6) of this paragraph. 

(3) Apparatus. Except as provided in subparagraph (7) of this paragraph, tests must be 

conducted in a draft-free cabinet in accordance with Federal Test Method Standard 191 Model 

5903 (revised Method 5902) for the vertical test, or Method 5906 for horizontal test (available 

from the General Services Administration, Business Service Center, Region 3, Seventh & D 

Streets SW., Washington, DC 20407). Specimens which are too large for the cabinet must be

tested in similar draft-free conditions. 

(4) Vertical test. A minimum of three specimens must be tested and results averaged. For 

fabrics, the direction of weave corresponding to the most critical flammability conditions must 

be parallel to the longest dimension. Each specimen must be supported vertically. The specimen 

must be exposed to a Bunsen or Tirrill burner with a nominal 3/8-inch I.D. tube adjusted to give 

a flame of 1 1/2 inches in height. The minimum flame temperature measured by a calibrated 

thermocouple pyrometer in the center of the flame must be 1550 °F. The lower edge of the

specimen must be 3/4-inch above the top edge of the burner. The flame must be applied to the 

centerline of the lower edge of the specimen. For materials covered by paragraph (a)(1)(i) of

part I of this appendix, the flame must be applied for 60 seconds and then removed. For 

materials covered by paragraph (a)(1)(ii) of part I of this appendix, the flame must be applied for 

12 seconds and then removed. Flame time, burn length, and flaming time of drippings, if any, 

may be recorded. The burn length determined in accordance with subparagraph (7) of this 

paragraph must be measured to the nearest tenth of an inch. 

(5) Horizontal test. A minimum of three specimens must be tested and the results averaged.

Each specimen must be supported horizontally. The exposed surface, when installed in the 

aircraft, must be face down for the test. The specimen must be exposed to a Bunsen or Tirrill 

burner with a nominal 3/8-inch I.D. tube adjusted to give a flame of 1 1/2 inches in height. The 

minimum flame temperature measured by a calibrated thermocouple pyrometer in the center of 

the flame must be 1550 °F. The specimen must be positioned so that the edge being tested is 

centered 3/4-inch above the top of the burner. The flame must be applied for 15 seconds and 

then removed. A minimum of 10 inches of specimen must be used for timing purposes, 

approximately 1 1/2 inches must burn before the burning front reaches the timing zone, and the 

average burn rate must be recorded. 

(6) Forty-five degree test. A minimum of three specimens must be tested and the results 

averaged. The specimens must be supported at an angle of 45° to a horizontal surface. The 

exposed surface when installed in the aircraft must be face down for the test. The specimens 

must be exposed to a Bunsen or Tirrill burner with a nominal 3/8-inch I.D. tube adjusted to give 

a flame of 1 1/2 inches in height. The minimum flame temperature measured by a calibrated 

B-5
thermocouple pyrometer in the center of the flame must be 1550 °F. Suitable precautions must

be taken to avoid drafts. The flame must be applied for 30 seconds with one-third contacting the 

material at the center of the specimen and then removed. Flame time, glow time, and whether 

the flame penetrates (passes through) the specimen must be recorded. 

(7) Sixty-degree test. A minimum of three specimens of each wire specification (make and size) 

must be tested. The specimen of wire or cable (including insulation) must be placed at an angle 

of 60-degree with the horizontal in the cabinet specified in subparagraph (3) of this paragraph 

with the cabinet door open during the test, or must be placed within a chamber approximately 2 

feet high by 1 foot by 1 foot, open at the top and at one vertical side (front), and which allows

sufficient flow of air for complete combustion, but which is free from drafts. The specimen must

be parallel to and approximately 6 inches from the front of the chamber. The lower end of the 

specimen must be held rigidly clamped. The upper end of the specimen must pass over a pulley 

or rod and must have an appropriate weight attached to it so that the specimen is held tautly

throughout the flammability test. The test specimen span between lower clamp and upper pulley

or rod must be 24 inches and must be marked 8 inches from the lower end to indicate the central 

point for flame application. A flame from a Bunsen or Tirrill burner must be applied for 30 

seconds at the test mark. The burner must be mounted underneath the test mark on the specimen, 

perpendicular to the specimen and at an angle of 30° to the vertical plane of the specimen. The 

burner must have a nominal bore of 3/8-inch and be adjusted to provide a 3-inch high flame with 

an inner cone approximately one-third of the flame height. The minimum temperature of the

hottest portion of the flame, as measured with a calibrated thermocouple pyrometer, may not be

less than 1750 °F. The burner must be positioned so that the hottest portion of the flame is 

applied to the test mark on the wire. Flame time, burn length, and flaming time of drippings, if 

any, must be recorded. The burn length determined in accordance with paragraph (8) of this 

paragraph must be measured to the nearest tenth of an inch. Breaking of the wire specimens is 

not considered a failure. 

(8) Burn length. Burn length is the distance from the original edge to the farthest evidence of

damage to the test specimen due to flame impingement, including areas of partial or complete 

consumption, charring, or embrittlement, but not including areas sooted, stained, warped, or 

discolored, nor areas where material has shrunk or melted away from the heat source. 

B-6
APPENDIX C—14 CFR PARTS 27 AND 29

§ 27.1365 Electric cables 

(a) Each electric connecting cable must be of adequate capacity. 

(b) Each cable that would overheat in the event of circuit overload or fault must be at least flame 

resistant and may not emit dangerous quantities of toxic fumes. 

(c) Insulation on electrical wire and cable installed in the rotorcraft must be self-extinguishing 

when tested in accordance with Appendix F, Part I (a)(3), of part 25 of this chapter. 

§ 29.831 Ventilation 

(a) Each passenger and crew compartment must be ventilated, and each crew compartment must

have enough fresh air (but not less than 10 cu. ft. per minute per crewmember) to let 

crewmembers perform their duties without undue discomfort or fatigue. 

(b) Crew and passenger compartment air must be free from harmful or hazardous concentrations 

of gases or vapors. 

(c) The concentration of carbon monoxide may not exceed one part in 20,000 parts of air during

forward flight. If the concentration exceeds this value under other conditions, there must be 

suitable operating restrictions. 

(d) There must be means to ensure compliance with paragraphs (b) and (c) of this section under 

any reasonably probable failure of any ventilating, heating, or other system or equipment. 

 § 29.863 Flammable fluid fire protection 

(a) In each area where flammable fluids or vapors might escape by leakage of a fluid system, 

there must be means to minimize the probability of ignition of the fluids and vapors, and the

resultant hazards if ignition does occur. 

(b) Compliance with paragraph (a) of this section must be shown by analysis or tests, and the 

following factors must be considered: 

(1) Possible sources and paths of fluid leakage, and means of detecting leakage. 

(2) Flammability characteristics of fluids, including effects of any combustible or 

absorbing materials. 

(3) Possible ignition sources, including electrical faults, overheating of equipment, and 

malfunctioning of protective devices. 

(4) Means available for controlling or extinguishing a fire, such as stopping flow of 

fluids, shutting down equipment, fireproof containment, or use of extinguishing agents. 

C-1
(5) Ability of rotorcraft components that are critical to safety of flight to withstand fire 

and heat. 

(c) If action by the flight crew is required to prevent or counteract a fluid fire (e.g. equipment

shutdown or actuation of a fire extinguisher), quick acting means must be provided to alert the 

crew. 

(d) Each area where flammable fluids or vapors might escape by leakage of a fluid system must

be identified and defined. 

 

C-2
APPENDIX D—FLAMMABILITY, SMOKE, AND DRY ARC TRACKING TESTS OF

AIRCRAFT ELECTRICAL WIRE INSULATIONS

D-1
DOT/FAA/CT-89/21 

FAA Technical Center

Atlantic City International Airport,

N.J. 08405 

Flammability, Smoke, and Dry 

Arc Tracking Tests of Aircraft 

Electrical Wire Insulations 

Patricia Cahill

July 1989 
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 object of this report. 
Technical Report Documentation Page 1. Report No.

DOT/FAA/CT-89/21 

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

 4. Title and Subtitle

FLAMMABILITY, SMOKE AND DRY ARCH TRACKING TESTS OF 

5. Report Date 

 July 1989

AIRCRFT ELECTRICAL WIRE INSULATIONS 6. Performing Organization Code

7. Author(s)

Patricia L. Cahill

8. Performing Organization Report No. 

 DOT/FAA/CT-89/21 9. Performing Organization Name and Address

Federal Aviation Administration

10. Work Unit No. (TRAIS) 

 

Technical Center 

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

 Final Report 

Technical Center 

Atlantic City International Airport, NJ 08405

14. Sponsoring Agency Code

15. Supplementary Notes 

16. Abstract

Although three different laboratory-scale tests were evaluated in this wire 

program, only the sixty-degree test is currently required by the Federal Aviation 

Administration (FAA). All test specimens with the exception of MIL-W-5086/1-PVC 

nylon passed this test with average burn lengths within the 3-inch maximum and 

no flame time. The MIL-W-5086/1 samples marginally passed the 30-second flame 

time, and the average burn length was greater than the 3-inch maximum specified 

in the FAR. 

The smoke test method used in this program called for a straight pilot burner 

when testing insulated conductor specimens. However, data for a multidirectional 

pilot burner were also included in this report. Large variations in Ds occurred 

between the two burners for ETFE constructions at both the 5- and 20-minute test 

points. The MIL-W-81381/12 aromatic polyimide and the composite construction 

(Teflon/polyimide/Teflon or TPT) showed no appreciable difference in Ds between 

the two burner types. Moreover, test duration did not affect smoke generation 

for these two samples. 

A direct correlation can be seen between the dry arc tracking tests and wet arc 

tracking tests (DOT/FAA/CT-88/4). The halogenated polymers formed no conductive 

chars upon thermal decomposition and, therefore, no dry arc tracking. The MIL-W81381/12 aromatic polyimide samples formed a conductive char upon thermal 

degradation, and severe arc tracking occurred. Extensive damage to all wires in 

the bundle occurred due to arc tracking propagation upon circuit breaker 

resetting. The TPT composite construction performed well. No dry arc tracking 

was evident. This construction behaved similarly to a halogenated polymer in 

this respect. 

17. Key Words 

Dry Arc Tracking 

Sixty-degree Flammability Tests 

Electrical Wire Insulations 

Smoke Test 

18. Distribution Statement 

Document is available to the U.S. public

through the National Technical Information

Service, Springfield, VA 22161. 

19. Security Classif. (of this report)

 Unclassified 

20. Security Classif. (of this page)

 Unclassified 

21. No. of Pages 

 21 

22. Price

Form DOT F1700.7 (8-72) Reproduction of completed page authorized 
TABLE OF CONTENTS 

EXECUTIVE SUMMARY v 

INTRODUCTION 1 

Purpose 1

Background 1 

DISCISSION 1 

Test Descriptions 1

Test Procedures 1

Test Samples 2

Test Results 3 

SUMMARY 4 

CONCLUSIONS 5

APPENDIX 

A – Sixty-degree Test

iii
LIST OF ILLUSTRATIONS 

Figure Page 

1 Test Drive 6 

2 TPT Photograph 15 

3 MIL-W-81381/12 Photograph 15 

4 MIL-W-22759/16 Photograph 16 

5 MIL-W-5086/1 Photograph 16 

6 MIL-W-22759/41 Photograph 17 

7 Lab Sample Photograph 17 

LIST OF TABLES 

Table Page 

1 Test Sample Summary - Sixty-Degree Test 7

2 Test Sample Summary - Smoke Test 8

3 Test Sample Summary - Dry Arc Tracking Test - TPT 9

4 Test Sample Summary - Dry Arc Tracking Test – MIL-W-81381/12 10

5 Test Sample Summary - Dry Arc Tracking Test – MIL-W-22759/16 11

6 Test Sample Summary - Dry Arc Tracking Test – MIL-W-5086/1 12

7 Test Sample Summary - Dry Arc Tracking Test – MIL-W-22759/41 13

8 Test Sample Summary - Dry Arc Tracking Test – Laboratory Sample 14

iv
EXECUTIVE SUMMARY

New material technology and new Federal Aviation Regulations (FAR) have focused 

attention on the need to explore additional types of wire insulation testing. 

This report contains the results of an evaluation of flammability, smoke 

characteristics, and dry arc tracking of aircraft electrical wire insulations. 

The sixty-degree flammability test, as specified in the FAR (appendix A), is the 

only flammability test required at the present time. All test specimens with 

the exception of MIL-W-5086/1-PVC nylon passed the sixty-degree test. The 

average burn length of the PVC nylon specimen was greater than the 3-inch 

maximum specified in the FAR. 

Smoke tests were run in the National Bureau of Standards (NBS) smoke chamber. 

Flaming combustion was evaluated in this program. Specific optical density (Ds) 

was evaluated at both the 5- and 20-minute test points. While the smoke test 

method employed calls for a straight pilot burner when testing insulated 

conductor specimens, tests were also run with the multidirectional pilot burner. 

When tested with both burner types at the 20-minute test point, MIL-W-81381/12 

aromatic polyimide and the composite construction Teflon outer wrap/polyimide 

middle wrap/Teflon inner wrap (TPT) had Ds values of under one. Large 

variations in Ds values between the 5- and 20-minute test points occurred for 

ethylene-tetrafluoroethylene (ETFE) constructions when testing with both types 

of burners. Also, Ds values were significantly higher for both modified and 

unmodified ETFE constructions when tested with the straight versus the 

multidirectional burner. 

Dry arc tracking test results compared well with wet arc tracking test results 

(DOT/FAA/CT-88/4 “Aircraft Electrical Wet-Wire Arc Tracking;”). Severe dry arc 

tracking occurred for all MIL-W-81381/12 aromatic polyimide samples. Extensive 

damage to all wires in the bundles was evident. The TPT composite and the 

halogenated polymer constructions formed no conductive char upon thermal 

degradation and therefore, no arc tracking occurred. 

v
INTRODUCTION

PURPOSE.

The objective of this project was to evaluate flammability, smoke characteristics, 

and dry arc tracking resistance of aircraft electrical wire insulations. 

BACKGROUND. 

At the present time, the only flammability test required for wire insulation is the 

sixty-degree test in compliance with Part 25.1359(d) in Appendix F of the Federal 

Aviation Regulations (FAR). With the advent of new material technology and new 

Federal Aviation Administration (FAA) regulations requiring more stringent 

flammability and smoke testing of aircraft materials, a need for additional types of 

wire insulation testing would seem apparent. Two candidates for these additional 

types of wire insulation testing are a smoke test and a dry arc tracking test. 

DISCUSSION 

TEST DESCRIPTIONS. 

SIXTY-DEGREE TEST. The sixty-degree test evaluates (1) ease of ignition, (2) flame 

propagation, (3) self-extinguishment time upon flame removal, and (4) flame time of 

drippings. This test has shown itself to be a quick and effective means for 

screening flammability characteristics of wire insulations. 

SMOKE TEST. In recent years, increased attention has been focused on the effects of 

smoke emanating from burning aircraft materials. In the confined environment of an 

aircraft cabin, it is imperative that smoke emission from all sources be minimized 

as the smoke may cause passenger panic and obscure exits and routes of escape. 

Transport category aircraft contain miles of wiring, therefore, limiting the smoke 

produced by wiring insulation in a fire would help to minimize the effects discussed 

above. 

DRY ARC TRACKING TEST. One problem that the United States Navy has encountered is 

the phenomenon of wet arc tracking (DOT/FAA/CT-88/4 “Aircraft Electrical Wet-Wire 

Arc Tracking”). While wet arc tracking is not a common occurrence in commercial 

aircraft, a dry arc tracking test would be beneficial in that a wire insulation’s 

tendency to form a char upon thermal degradation could be characterized. Thermal 

degradation is primarily initiated by the extremely high temperature of an 

electrical arc. Upon thermal breakdown, a wire insulation will (1) decompose and 

give off gaseous byproducts or (2) form a char which may be conductive. If the 

initial arc were to trip one or more circuit breakers, resetting of the breakers, 

may result in severe damage propagation to the wire bundle if a conductive char is 

present. This phenomenon is known as arc tracking. 

TEST PROCEDURES.

SIXTY-DEGREE TEST. The sixty-degree test was performed in accordance with the 

procedure specified in Appendix F of Part 25 of the FAR. Refer to appendix A for 

the test description. 

 1
SMOKE TEST. The Smoke test was performed in accordance with the procedure specified 

in the American Society for Testing and Materials (ASTM) Standards F814 titled, 

“Standard Test Method for Specific Optical Density of Smoke Generated by Solid 

Materials for Aerospace Applications.” Refer to this method for the test 

description. Only the flaming condition was evaluated in this program. While this 

procedure calls for a straight pilot burner when testing insulated conductor 

specimens, data for a multidirectional pilot burner is included in the test results. 

DRY ARC TRACKING TEST. This test was performed using a seven-wire bundle cut to a 

length of 14 inches. Insulation of 3/16 inches was stripped from both ends of each 

wire. The wires were tied in a six-around-one configuration using an appropriate 

tying material (waxed linen lacing cord, nylon lacing cord, plastic tie-wraps, etc.) 

with the tie nearest the end of the bundle, 1/4 inch back on the insulation from the 

stripped wire ends. A second tie was made around the bundle 2 inches farther back 

from the first tie. The tie material used was the waxed linen lacing cord. 

After the bundle was tied, all the exposed wire ends on one side of the bundle were 

splayed out such that the strands of each conductor were interming1ed with those of 

adjacent conductors. A small amount of finely powdered conductive graphite was 

applied to the splayed wire ends to insure that an arc was struck. The bundle was 

then supported horizontally in a lab stand using two clamps approximately 8 inches 

apart. 

Power was supplied through a 115/220-volt, 400-cycle motor-generator rated at 

18.75 kVA. It was located approximately 50 feet from the test stand and was 

wired to the test bench through a 75- and a 20-ampere circuit breaker inside the 

generator control box. Individual fuses in a separate fuse box for each phase, a 

heavy duty manual on-off switch at the test bench, and seven 7-1/2 ampere Klixon

aircraft circuit breakers in a box on the test bench completed the electrical 

configuration. 

Two breakers were connected to phase “A,” two to phase “B,” two to phase “C,” and 

one to neutral. All seven test leads had alligator clips on the ends to facilitate 

connecting to the wires being tested. The test leads were randomly connected to the 

seven wires in the test bundle. A 3- by 4-foot shield was placed in front of the 

test setup to protect personnel from the molten metal and burned insulation thrown 

off when the test arc occurred. Figure 1 is a photograph of the test device. 

The test arc was initiated by closing the heavy duty manual switch at the test 

bench. After the initial arc was struck, only one attempt was made to reset any 

open circuit breakers. Ten tests were run on each wire sample. 

TEST SAMPLES. 

Six wire types were evaluated in this test program. Four of these constructions are 

currently in service wires: 

MIL-W-81381/12 - Kapton aromatic polyimide - liquid H-301 topcoat 

MIL-W-22759/41 - Extruded radiation cross-linked ETFE 

MlL-W-22759/16 - Extruded Tefzel (ETFE) 

MIL-W-5086/1 - PVC nylon 

 2
The fifth wire type evaluated was an experimental composite construction 

consisting of a Teflon outer wrap/polyimide middle wrap/Teflon inner wrap 

(TPT). The sixth wire type was a proprietary cross-linked irradiated ethylenetetrafluoroethylene (ETFE). All test specimens were American Wire Gauge (AWG) 

20 interconnect wires. 

TEST RESULTS.

SIXTY-DEGREE TEST. Table 1 summarizes the results of the sixty-degree test. 

The average burn length of all samples, with the exception of MIL-W-5086/1 was 

within the 3-inch maximum specified in the FAR. The average burn length of the 

MIL-W-5086/1 samples was 5.1 inches, which exceeds the 3-inch maximum. 

No flame time after removal of the flame source was recorded for the samples, 

with the exception of MIL-W-5086/1. The average flame time for MIL-W-5086/1 

was 26 seconds. This is within the 30-second time limit defined in the FAR. 

No drippings from any of the test samples were detected. 

SMOKE TEST. Table 2 summarizes the results of the smoke tests performed on the 

wire test samples. While the ASTM method employed specifies a straight flame 

burner, some laboratories use the multidirectional burner. Therefore, data for 

both burners are presented. From table 2, the specific optical density (Ds) 

for TPT and MIL-W-81381/12 does not significantly vary when comparing 5-minute 

with 20-minute values for both types of burners. Both TPT and MIL-W-81381/12 

produced extremely small amounts of smoke. In both cases, Ds values were under 

one. When tested with both burner types, MIL-W-5086/1 generated large 

quantities of dark smoke. Specific optical density values reached the highest 

number capable of computer generation at the 5-minute test interval (Ds=776.5) 

therefore, samples were not run for 20 minutes. The MIL-W-22759/16 samples 

showed a large variation in Ds values between the 5- and 20-minute test 

intervals for both burners. Moreover, significant differences in Ds values 

occurred between the two different burners at both the 5- and 20-minute test 

points with the straight burner producing higher Ds values. 

The MIL-W-22759/41 test samples also showed a noticeable difference in Ds

values between the 5- and 20-minute test points. This difference occurred with 

both burner types: again, the straight burner producing higher Ds values than 

the multidirectional burner. The extruded radiation crosslinked ETFE 

laboratory samples produced large quantities of smoke. At the 20-minute test 

point, Ds values for both burners were 775.0. At the 5-minute test point, the 

Ds was significantly higher with the straight burner (55.5) than the 

multidirectional burner (7.7). 

DRY ARC TRACKING TEST. Tables 3 through 8 summarize the results of the dry arc 

tracking tests and figures 2 through 7 are photographs of the wire bundles 

after testing. Table 3 presents the data for the on1y composite construction 

among the test specimens. This wire sample incorporated a Teflon outer 

wrap/polyimide middle wrap/Teflon inner wrap. No dry arc tracking was found. 

The initial arcs struck were all moderate in severity. Figure 2 shows the TPT 

wire bundles after testing. Note the appearance of welds and some tube effects 

(i.e., vaporization of conductor with insulation material remaining). No 

evidence of carbonization was found on the wire insulation. Data on MIL-W81381/12 (aromatic polyimide) samples are presented in table 4. All initial 

arcs were massive in severity and caused multiple circuit breakers to trip. 

Carbonization of the po1yimide due to the temperature of the initial arc 

3
occurred each time. Upon resetting of the circuit breakers, severe re-arcing 

took place resulting in more insulation degradation. The polyimide samples are 

shown in figure 3. Tables 5, 6, and 7 summarize arc tracking data on three 

halogenated polymers. All insulation systems are currently in service. 

Initial arcs were mild to moderate for all three sets of samples. No dry arc 

tracking was found for any of the test specimens. Upon resetting of tripped 

circuit breakers, tables 5, 6, and 7 show that all breakers either stayed in, 

retripped immediately, or resulted in a small arc restrike followed by a 

circuit breaker retrip. Figures 4, 5, and 6 show the wire bundles after 

testing. Note the similar appearance of all three specimens with the welds and 

tube effects. Minimal insulation damage is seen for all samples. Table 8 

presents the data on the laboratory sample of extruded radiation crosslinked 

ETFE. Five tests were performed due to a shortage of sample wire. Initial 

arcs were mild to moderate. No dry arc tracking was found. Upon resetting of 

tripped circuit breakers all breakers retripped immediately or stayed in. The 

wire bundles are shown in figure 7. 

SUMMARY

Although three different laboratory-scale tests were evaluated in this wire 

program, only the sixty-degree test is currently required by the Federal 

Aviation Administration (FAA). All test specimens with the exception of MIL-W5086/1-PVC nylon passed this test with average burn lengths within the 3-inch 

maximum and no flame time. The MIL-W-5086/1 samples marginally passed the 30-

second flame time, and the average burn length was greater than the 3-inch 

maximum specified in the FAR. 

The smoke test method used in this program called for a straight pilot burner 

when testing insulated conductor specimens. However, data for a 

multidirectional pilot burner were also included in this report. Large 

variations in Ds occurred between the two burners for ETFE constructions at 

both the 5- and 20-minute test points. The MIL-W-81381/12 aromatic polyimide 

and the composite construction (Teflon/polyimide/Teflon or TPT) showed no 

appreciable difference in Ds between the two burner types. Moreover, test 

duration did not affect smoke generation for these two samples. 

A direct correlation can be seen between dry arc tracking tests and wet arc 

tracking tests (DOT/FAA/CT-88/4). The halogenated polymers formed no 

conductive chars upon thermal decomposition and, therefore, no dry arc 

tracking. The MIL-W-81381/12 aromatic polyimide samples formed a conductive 

char upon thermal degradation, and severe arc tracking occurred. Extensive 

damage to all wires in the bundle occurred due to arc tracking propagation upon 

circuit breaker resetting. The TPT composite construction performed well. No 

dry arc tracking vas evident. This construction behaved similarly to a 

halogenated polymer in this respect. 

4
CONCLUSIONS

1. Specific optical density (Ds) of both modified and unmodified ethylenetetrafluoroethylene (ETFE) polymers varies significantly when tested with the 

straight versus the multidirectional pilot burner. 

2. No difference in Ds was seen for either Kapton aromatic polyimide or the 

composite construction Teflon outer wrap/polyimide middle wrap/Teflon inner 

wrap (TPT) when tested with both burn holders. 

3. No dry arc tracking was seen for any of the specimens tested with the 

exception of the MIL-W-81381/12 Kapton samples. 

4. The Teflon fluoropolymer tapes of the TPT construction prevented dry arc 

tracking. 

5
FIGURE 1. TEST DEVICE 

6
TABLE 1. TEST SAMPLE SUMMARY - SIXTY-DEGREE TEST 

Material Burn Length 

Specification (Average of 3 tests) Flame Time Drippings

TPT 1.3 inches 0 0 

MIL-W-81381/12 1.4 inches 0 0 

MIL-W-22759/16 2.0 inches 0 0 

MIL-W-5086/1 5.1 inches 26 seconds 0 

MIL-W-22759/41 1.7 inches 0 0 

Lab Sample - 1.6 inches 0 0 

extruded radiation 

crosslinked ETFE 

7
TABLE 2. TEST SAMPLE SUMMARY - SMOKE TEST 

Flaming Combustion Straight Pilot Burner 

 Material 5-minute Ds 20-minute Ds 

Specification (Average of 3 Tests) (Average of 3 Tests) 

 TPT 0.19 0.84 

MIL-W-81381/12 0.05 0.36 

MIL-W-22759/16 68.60 364.39 

MIL-W-5086/1 776.20 not run 

(PVC) nylon 

MIL-W-22759/41 11.14 182.37 

Lab Sample - 55.50 775.00 

extruded radiation 

crosslinked ETFE 

Multidirectional Pilot Burner 

Material 5-minute Ds 20-minute Ds 

Specification (Average of 3 Tests) (Average of 3 Tests) 

 TPT 0.013 0.85 

MIL-W-81381/12 0.13 0.13 

MIL-W-22759/16 18.67 207.12 

MIL-W-5086/1 776.52 not run 

MIL-W-22759/41 2.86 105.56 

Lab Sample - 7.70 775.00 

extruded radiation 

crosslinked ETFE 

8
TABLE 3. TEST SAMPLE SUMMARY - DRY ARC TRACKING TEST 

Teflon/Polyimide/Teflon (TPT) 

Wire 

Bundle Initial Arc

Tripped Circuit Breakers 

(Upon Initial Arc)

Arc 

Track

Notes 

(CB's reset 1 time)

1 moderate 0 no

2 Moderate 0 no

3 moderate 0 no

4 moderate 0 no

5 moderate 0 no

6 moderate 1 no CB stayed in 

7 moderate 0 no

8 moderate 2 no Small arc restrike 

and retrip. CB 

retripped. 

9 moderate 0 no

10 moderate 0 no

9
TABLE 4. TEST SAMPLE SUMMARY - DRY ARC TRACKING TEST 

MIL-W-81381/12 - Kapton/aromatic polyimide 

Wire 

Bundle Initial Arc

Tripped Circuit Breakers

(Upon Initial Arc)

Arc 

Track

Notes 

(CB's reset 1 time)

1 massive 4 yes Severe rearcing, 

all breakers 

retripped. 

2 massive 6 yes Severe rearcing, 

all breakers 

retripped. 

3 massive 4 yes Severe rearcing, 

all breakers 

retripped. 

4 massive 6 yes Severe rearcing, 

all breakers 

retripped. 

5 massive 6 yes Severe rearcing, 

all breakers 

retripped. 

6 massive 6 yes Severe rearcing, 

all breakers 

retripped. 

7 massive 6 yes Severe rearcing, 

all breakers 

retripped. 

8 massive 6 yes Severe rearcing, 

all breakers 

retripped. 

9 massive 6 yes Severe rearcing, 

all breakers 

retripped. 

10 massive 6 yes Severe rearcing, 

all breakers 

retripped. 

10
TABLE 5. TEST SAMPLE SUMMARY - DRY ARC TRACKING TEST 

MIL-W-22759/16 – TEFZEL (ETFE) 

Wire 

Bundle Initial Arc

Tripped Circuit Breakers 

(Upon Initial Arc)

Arc 

Track

Notes 

(CB's reset 1 time)

1 moderate 1 no CB’s stayed in. 

2 moderate 2 no Small arc restrikes 

and retrip. CB 

stayed in. 

3 moderate 0 no

4 moderate 1 no CB’s stayed in. 

5 moderate 3 no All CB’s stayed in. 

6 moderate 0 no

7 moderate 2 no Small arc restrikes 

and retrips for both 

CBs. 

8 mild 0 no

9 moderate 2 no Both CB’s stayed in. 

10 moderate 1 no Immediate retrip. 

11
TABLE 6. TEST SAMPLE SUMMARY - DRY ARC TRACKING TEST 

MIL-W-5086/1 – PVC Nylon 

Wire 

Bundle Initial Arc

Tripped Circuit Breakers

(Upon Initial Arc)

Arc 

Track

Notes 

(CB's reset 1 time)

1 moderate 0 no

2 mild 0 no

3 mild 0 no

4 moderate 0 no

5 moderate 1 no CB stayed in. 

6 mild 0 no

7 mild 1 no CB stayed in. 

8 mild 0 no

9 mild 0 no

10 mild 0 no

12
TABLE 7. TEST SAMPLE SUMMARY - DRY ARC TRACKING TEST 

MIL-W-22759/41 – Extruded radiation crosslinked ETFE 

Wire 

Bundle Initial Arc

Tripped Circuit Breakers

(Upon Initial Arc)

Arc 

Track

Notes 

(CB's reset 1 time)

1 mild 0 no

2 moderate 0 no

3 moderate 1 no CB stayed in. 

4 mild 2 no Immediate retrip, 

CB stayed in. 

5 mild 0 no

6 moderate 0 no

7 moderate 0 no

8 moderate 0 no

9 mild 0 no

10 moderate 0 no

13
TABLE 8. TEST SAMPLE SUMMARY - DRY ARC TRACKING TEST 

Extruded radiation crosslinked ETFE 

Wire 

Bundle Initial Arc

Tripped Circuit Breakers

(Upon Initial Arc)

Arc 

Track

Notes 

(CB's reset 1 time)

1 moderate 0 no

2 mild 4 no All CB’s 

immediately 

retripped. 

3 mild 4 no All CB’s 

immediately 

retripped. 

4 mild 4 no CB stayed in. 

CB retripped. 

CB stayed in. 

CB stayed in. 

5 mild 1 no CB stayed in. 

14
FIGURE 3. MIL-W-81381/12 PHOTOGRAPH FIGURE 2. TPT PHOTOGRAPH 

15
FIGURE 5. MIL-W-5086/1 PHOTOGRAPH FIGURE 4. MIL-W-22759/16 PHOTOGRAPH 

16
FIGURE 7. LAB SAMPLE PHOTOGRAPH FIGURE 6. MIL-W-22759/41 PHOTOGRAPH 

17
APPENDIX A – SIXTY DEGREE TEST

Chapter 1 – Federal Aviation Administration Part 25, App. G 

(g) Sixty-degree test in compliance with Part 25.1359(d). A minimum of three 

specimens of each wire specification (make and size) must be tested. The 

specimen of wire or cable (including insulation) must be placed at an angle of 

60° with the horizontal in the cabinet specified in paragraph(c) of this 

appendix with the cabinet door open during the teat or must be placed within a 

chamber approximately 2 feet high x 1 foot x 1 foot, open at the top and at 

one vertical side (front), and which allows sufficient flow of air for 

complete combustion, but which is free from drafts. The specimen must be 

parallel to and approximately 6 inches from the front of the chamber. The 

lower end of the specimen must be held rigidly clamped. The upper end of the 

specimen must pass over a pulley or rod and must have an appropriate weight 

attached to it so that the specimen is held tautly throughout the flammability 

test. The test specimen span between lower clamp and upper pulley or rod must 

be 24 inches and must be marked 8 inches from the lower end to indicate the 

central point for flame application. A flame from a Bunsen or Tirrill burner 

must be applied to 30 seconds at the test mark. The burner must be mounted 

underneath the test mark on the specimen, perpendicular to the specimen and at 

an angle of 30° to the vertical plane of the specimen. The burner must have a 

nominal bore of three-eighths inch and must be adjusted to provide a 3-inchhigh flame with an inner cone approximately one-third of the flame height. 

The minimum temperature of the hottest portion of the flame, as measured with 

a calibrated thermocouple pyrometer, may not be less than 1,750°F. The burner 

must be positioned so that the hottest portion of the flame is applied to the 

test mark on the wire. Flame time, burn length, and flaming time of 

drippings, if any, must be recorded. The burn length determined in accordance 

with paragraph(h) of the appendix must be measured to the nearest one-tenth 

inch. Breaking of the wire specimens is not considered a failure. 

(h) Burn length. Burn length is the distance from the original edge to the 

farthest evidence of damage to the test specimen due to flame impingement, 

including areas of partial or complete consumption, charring, or 

embrittlement, but not including areas sooted, stained, warped, or discolored, 

nor areas where material has shrunk or melted away from the heat source. 

ÕU.S. GOVERNMENT PRINTING OFFICE: 1989-0-606-911 

A-1