AIRCRAFT ELECTRICAL WIRE TYPES

AIRCRAFT ELECTRICAL FIRES

 

An aviation safety article

Alex PATERSON

http://alexpaterson.net/aviation/wire_types.htm

Last Updated: 22 July 2012

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MASTER INDEX of articles written, posted online, or recommended by Alex Paterson

INTRODUCTION

This article provides a list of electrical wire types most commonly used in jet transport aircraft. The articles lists both the positive and negative characteristics of each wire type and the aircraft that these wires have been installed in. It needs to be understood that the article is by necessity incomplete because aircraft manufacturers and airlines have historically given scant regard to the potential dangers posed by different wire types when installing them in their aircraft and therefore have not kept accurate records of what types of wire have been installed in the same. The complacency within the aviation industry towards the dangers posed by electrical wire is endemic and is best summed up by the comment of United States Federal Aviation Authority (FAA) deputy head, Tom McSweeny, who is reported to have said before a Congressional Committee in 19-- that "wire is wire". (more on Mr McSweeny's alleged comment below)

NOTE: This is a draft web page only, setup for discussion between contributors. It undoubtedly contains omissions, and possibly some mistakes.  

Readers are invited to agree with, disagree with, seek clarification about or put their point of view about any of the issues discussed in the article.

Alex Paterson (May 2007)

AIRCRAFT WIRE TABLE

The following table relates to general purpose aircraft electrical wire. It is important to understand that all transport jet and turboprop aircraft have a mixture of the following different wire types installed in them. The wire types listed in the table relate to the predominant type of wire used in each aircraft. It would appear that even aircraft manufacturers themselves are not completely sure as to what wire is installed in individual aircraft as their attitude towards electrical wire in the past has been that "wire is wire".

Table Colour code:

NOTE: Wire is listed in the table by date of introduction into aircraft, with the oldest wire typed listed at the top.

WIRE TYPE	DESCRIPTION	AIRCRAFT INSTALLED IN (some)
PVC/Nylon (Polyvinyl-Chloride) Introduced 1950s Specification No: 5086	Fails Far 25 Weight 6.8 lbs. per 1,000 ft (Heaviest and thickest) Rated temperature low: 105°C Flammable - burns readily creating copious amounts of thick, toxic smoke rendering it virtually impossible for pilots to see their flight instruments or breathe. (e.g. Valujet 592) Insulation when burning turns to hydrochloric acid when exposed to water. Outgasses onto electrical & electronic contacts Soft - Susceptible to chafing Susceptible to aging in that it dries out and becomes brittle. Banned by US Air Force. US Air Force had 800 autopilot anomalies due to defective PVC in a 6 month study in --? Still used as general purpose replacement wire. Implicated in Valujet Flight 592 DC9 which crashed into the Florida Everglades on 11 May 1996 Dangerous Wire	Installed in Early DC-9s up until 1979 (e.g. Valujet 592) Early B727s up until 1976 Early B737s up until 1976 Still used as general purpose replacement wire by sections of the aviation industry.
Kynar Introduced in 1964 Specification number: 81044/9	Fails Far 25 Thickness: 15 microns Weight 5.5 lbs per 1,000 ft. Rated Temperature: 150°C (fails temperature spec) Poor fluid resistance No longer used	Installed in DC9s from 1970 until 1976
Kapton (complex aromatic polyamide) Manufactured by Dupont Chemical Co. Introduced 1966 Specification Numbers: 81381/11 BMS 13-51 (Boeing)	Fails Far 25 Thickness: 8.4 microns (Very thin) Weight: 4.6 lbs per 1,000 ft (Very light weight) Rated temperature: 200°C 'Explodes' and burns fiercely at flash-over during an arc tracking event due to the production of free hydrogen, severely damaging adjacent wires and igniting surrounding structure. (i.e. behaves like detonator fuse.) 1 High ignition temperature to start burning (usually associated with an electrical short circuit of 5000°C), but when it does finally ignite it burns very fiercely (explodes) creating virtually no smoke. Fumes are clear and fairly benign. Susceptible to wet and dry Arc Tracking. Susceptible to aging in that it dries out forming hairline cracks which can lead to micro current leakage (i.e. electrical 'ticking' faults ) which in turn can eventually culminate in an explosive arc tracking event. (i.e. short circuit) 1 Stiffness (straight line memory) makes it prone to vibration chafing, (rubbing) and stressed by bending. Abrasive to other wires. (due to its hardness) Hygroscopic (i.e. absorbs water ) rendering it susceptible to wet arc tracking. Installation difficulties (difficult to strip and mark) Banned by * US Air Force * US Navy * Canadian military * Boeing in 1992 * Bombardier? VERY DANGEROUS WIRE	Installed in Airbus A310 (all) Airbus A320 (currently) 2 Airbus A330 (currently) Airbus A340 (currently) B727 (after 1979, EB) B737 (after 1979 to 1990) B747-400 (some from 1989 - 1991) B757 (up until 1990) B767 (up until 1991) BAe 146 (unconfirmed reports) DC-10 MD-8x (all) MD-11 (up until early 1992) A300 -600 (with Teflon top-coat) L-1011 Tristar Concorde SST B-707 (but not according to EB) Dassault Mercure CL 600 Series (but not RJ/CL604 or Global Express (Challenger) Shorts SD-330 Gulfstream G-II, G-III HS125-700 Bell 212, 214 Sikorsky S-61, S-70B, S-76 Westland 606 Plus 31 military types such as P-3, C130, F-14, F-18, Hawkeye, etc Still used by AIRBUS in A319, A320, A330, A340 until about 2005 (see footnote 2 below)
Teflon (Polytetrafluoroethylene - PTFE) Introduced in 1969 Specification Numbers: 22759/11	Fails Far 25 Thickness: 10 microns Weight 5.43 lbs/1,000 ft. Rated temperature: 200°C Longitudinal splitting problem due to manufacturing process. Susceptible to cold-flow (creeping of conductor). Type of insulation found as ignition source on Apollo 13 Type of insulation found split in TWA 800-fuel tank wires [Fuel Quantity Indicating System] (FQIS) Banned by major manufacturers in 1983	Installed in B747 BAe146
Poly-X (alkane-imide) an Aliphatic polyimide Manufactured by Raychem Introduced in 1970 Specification Numbers: 81044/16-29	Fails Far 25 The first exotic blend of insulation (due to oil embargo) Thickness: 10 microns Weight: 4.7 lbs. per 1,000 ft (Light weight) Rated temperature: 150°C Susceptible to solvents Susceptible to radial cracking. Projected service life 60,000 hrs/but circumferential cracks found after just 2000 hrs by US Navy. Susceptible to premature aging. Banned by US Navy in 1978 due to premature aging of insulation after 4000 hrs Brittle. Due to brittleness, 1" bare spots not uncommon. Susceptible to chafing. Fails FAR 25 (airworthiness testing standards) Caused 323 USN F-14s to be re-wired Banned by US Navy. Implicated by Edward Block (and others) in the downing of TWA Flt 800 in 1996.  4 No longer used in civilian aircraft. Dangerous Wire	Installed in Early 747s (e.g. TWA 800) Early DC-10s
Stilan Introduced 1972 Specification Numbers: 81044/20	Fails Far 25 Thickness: 10 microns Weight 4.7 lbs. per 1,000 ft (Light weight) Rated Temperature: 150°C Insulation breaks down in hydraulic and de-icing fluid Microscopic crazing problem seen under microscope Cracks under stress Found to arc over Susceptible to spurious signal generation (EMI hazard) Absorbs water (i.e. hygroscopic) No longer used	Installed in B-747s built in mid-to-late 1970s DC-10s built in mid-to-late 1970s
Tefzel (ETFE) Introduced 1972   Specification numbers F-5	Fails Far 25 Rated temperature 150°C Soft at rated temperature Used as general installation wire but should never be mixed in bundle with other wire types due to its softness.	Installed in Arcturus Tefzel was found in Swiss Air flight SR111's Inflight Entertainment System (IFEN) which was suspected as being the cause of the inflight fire and subsequent crash of the aircraft off Nova Scotia in November 1998.
Cross Linked Tefzel (XL-ETFE) Manufactured by Judd Wire and Raychem. Known by some sections of the aviation industry as "Spec 55" wire. Apparently the name "Spec 55" has been trademarked by Raychem. Introduced 1977  Specification numbers MIL-W-22759/34 Spec 55 Spec 55A BMS 13-48 (Boeing)	Fails Far 25 Thickness: 10 microns Weight: 5.0 lbs/1000' (light weight) Rated temperature: 150°C Wet arc tracks Flammable producing copious amount of Dense toxic smoke (96%+ density) when it burns rendering it virtually impossible for flight crew to see their flight instruments. NASA states will fail flammability requirements in 30% oxygen. Toxicity - the worst of all wires, banned for manned aerospace use by major manufacturer. (Grumman Corporation banned it in 1982 and NASA followed suit in 1983 due to its toxicity) Soft at rated temperature Loses mechanical strength properties at rated temperature Fails FAR 25 (airworthiness standards test) Projected life 50,000 hrs Notch propagation problems Dangerous Wire	Installed in B737 (currently) B747 (currently) B757 (currently) B767 (currently) B777 (currently) BAe146 Airbus A320 Airbus A330 Airbus A340 Still used by BOEING in B737, B747, B757, B767, B777 and Airbus
TKT Boeing (Teflon/Kapton/Teflon) Introduced 1992 Boeing Specification No: MIL-W-22759 BMS 13-60 (Boeing) Tufflite brand manufactured by Tensolite http://www.tensolite.com	Passes FAR 25 Weight: 5.0 lbs. per 1,000 ft (Light weight) Arc-track resistant Abrasion resistant Superb insulation protection High heat tolerance Resists smoking when burning (less than 2% density) Displays all the positive aspects of Kapton (i.e. lightweight, resistance to burning, no fumes when burning etc) without any of Kapton's negatives. No known problems SAFE WIRE	Installed in B737s built after 1992 B757s built after 1992 Reported by some LAMEs to be partly installed in some B747-400 aircraft manufactured between 1989 - 1999. NOTE: Airbus Industries now use their own version of TKT (See below)
KKF BAe Two layers of Kapton within a FEP laquer topcoat. Installed within the pressure cabin of BAe 146 aircraft. Note: Source of info: BAe Statement dated 7 July 1999	FAR 25 attributes unknown Undoubtedly safer than Kapton if only because it reduces Kaptons propensity to dry out and form cracks. Resistance to Arc Tracking unknown.	Installed in BAe 146 Source: BAe Statement 7 July 1999
KT BAe Single layer of Kapton overlaid by single wrap of PTFE (i.e. Teflon) Installed outside the pressure cabin of BAe 146 aircraft. Note: Source of info: BAe Statement dated 7 July 1999	FAR 25 attributes unknown Undoubtedly safer than Kapton if only because it reduces Kapton's propensity to dry out and form cracks. However, similar to Airbus' KTT (see below) which according to the America's foremost independent aircraft wire expert, Edward Block, "this type of wire is just Kapton with a cosmetic coating of Teflon which is used for marking purposes only and does little to reduce Kapton's propensity to explosively arc track". Safety Unknown	Installed in BAe 146 Source: BAe Statement 7 July 1999
KTT Airbus Kapton with two very thin outer layers of Teflon. Called by Airbus Polimide/PTFE/PTFE Airbus Specification No: ASNE0261CF	FAR 25 attributes unknown Undoubtedly safer than Kapton, but Airbus refuses to disclose performance attributes or specifications of this wire to independent researchers. According to specifications available, this wire is made up of 25µm Kapton, sandwiched between two layers of 2.5µm FEP. Safety Unknown	Used by Airbus to replace Kapton as a general purpose wire. Installed in Airbus FBW aircraft up until mid 2006 when it was replaced by Airbus' TKT specification EN2267-008 listed below. See footnote 3 below.
TKT Airbus Called by Airbus PTFE/Polimide/PTFE Note: PTFE/Polimide/PTFE is just another name for TKT as Teflon is a PTFE and Kapton is a Polimide Airbus Specification No: EN2267-008	Probably meets FAR 25 Airbus refuses to fully disclose the performance attributes or specifications of this wire to independent researchers. No known specifications released by Airbus although suspected to be very similar to Boeing's TKT wire listed above. Allegedly has a much thicker outer layer of PTFE (i.e. Teflon) than the KTT wire used earlier by Airbus. (see below) Probably Safe	Reportedly now installed in Airbus Aircraft as from mid 2006 as a general purpose wire.

Sources:

• Edward Block (IASA) Edward B. Block is an international expert on aviation and wiring, specialising in aircraft crash investigations. 
• Captain John Sampson (IASA)  Is a practicing airline pilot with extensive experience in civil airline operations, helicopter piloting and military aviation.  Was editor of Aviation Safety Week for a period of time in the mid 2000s.
• Michael Murphy. Aviation safety auditor from Canada.
• Patrick Price (deceased) Ex-employee of Boeing Corporation tasked with investigating aircraft electrical wiring issues.

NOTES

FAR 25 comprises clauses mandating aircraft design safety rules. However, there are no specific clauses within FAR 25 pertaining to the flammability, toxicity or smoke visibility criteria of electrical wire insulation. That said, FAR Section 601 mandates a general statement that;

FAR 25-601: "The airplane may not have design features or details that experience has shown to be hazardous or unreliable. The suitability of each questionable design detail and part must be established by tests."

Source: http://www.flightsimaviation.com/data/FARS/part_25-601.html

As argued in this document the suitability of aircraft electrical wire insulation materials are "questionable", yet they have never been the subject of a comprehensive formal testing program and as such are in breach of FAR 25-601.

Only Boeing's TKT wire has no known problems and meets FAR 25 requirements. Airbus' version of TKT probably meets FAR 25 requirements.

No specific standards spelt out by aircraft regulatory authorities such as US FAA or European JAR regarding aircraft electrical wire. Specifically no standards defined or any requirement to test wire for:

• Propensity of wire to wet or dry arc track.
• Propensity of wire to burn.
• the density of smoke and toxicity of fumes when wire burns.

Modern jet transport aircraft are required by law (FAA 25 & JAR 25) to ensure all safety of flight items and aircraft systems have adequate backup systems installed in the event of a failure of the main system, (and that includes aircraft electrical systems), yet no thought was given to the failure of the aircraft wiring system itself.

Wire is deemed by most in the aviation industry (i.e. aircraft manufacturers, pilots, airline management and regulatory authorities) as an "install and forget" item. This attitude is best summed up by the comment of United States Federal Aviation Authority (FAA) deputy head, Tom McSweeny, who is reported to have said before a Congressional Committee that "Wire is wire". This attitude ignores the fact that:

• Modern jet transport aircraft contain literally hundreds of kilometers of wire.
• Wire is often damaged during manufacture and/or installation.
• Wire is often incorrectly installed in aircraft. (i.e. incorrectly routed near hot equipment and/or bundled together with other incompatible wire types such as soft wire laying adjacent hard wire etc)
• Wire (both the wire and its insulation) deteriorates with age. With regard to the insulation, it dries out, becomes brittle forming cracks exposing the conductor (i.e. wire) . Wire itself, oxidises especially associated with the widespread electrolysis that occurs in aircraft leading to poor contacts and the generation of local hot spots in the wire which has the potential to melt the surrounding insulation material.
• All wire deteriorates in service due to environmental factors such as:
  • extremes of heat & cold experienced by aircraft on the ground and in the air. (i.e. wire can experience plus +200°C down to minus -70°C),
  • water damage, (hydrolysis and the fact that some wire types exhibit hygroscopic tendencies)
  • salt damage associated with marine environments. (all aircraft operate into airfields adjacent marine environments at least some time in their operational lives)
  • contamination by aircraft fluids such as fuel, oil, hydraulic fluid, deicing fluid, cleaning chemicals, toilet residue, galley spillage etc.
  • inflight vibration causing chafing of wires rubbing against other wires or the structure of the aircraft. This is especially a problem with hard wire such as Kapton laying adjacent a soft wire like Tefzel.
  • All wire products display differing properties with regard to aging, but practically all wire insulation material dries out, goes hard and then develops hairline fractures which allow the ingress of water and other aviation fluids leading to micro-discharges of current through the cracks to surrounding wires or the aircraft structure. ('ticking' faults)
  • All aircraft use their airframe as their electrical earth return pathway resulting in significant constraints in the operation of protection devices such as circuit breakers located in the cockpit. (see separate paper on this issue)

According to Ed Block: "Only TKT wire insulation (BMS 13-60) meets FAR 25 Standards."

RECOMMENDATIONS

The aviation industry as a whole needs to acknowledge that the shortcomings associated with different electrical wire types are a serious issue and potentially very dangerous as evidenced by the information presented in this paper. The notion held by many with in the aviation industry that "wire is just wire" is irresponsible.

Practical steps that the industry should take to begin to address the situation include:

• Aviation regulatory authorities need to specify rigorous performance standards for electrical wire so that they conform to FAR 25 in that "insulation material is not used that is hazardous, unreliable, or contributes smoke/fire". Any promulgated standards for electrical wire would need to be rigorously enforced.
  
  
• Acknowledge that Kapton wire is a particularly dangerous hazard to aircraft and insist upon its its removal from aircraft where practical. (this statement acknowledges the fact that the complete removal of Kapton wire will be in many cases an impossibility)
  
  
• Insist that electronic 'Fly by Wire' (FBW) aircraft be fitted with a completely separate 'virgin' emergency electrical bus to allow pilots to remove all electrical current from all 'normal' electrical wire circuits in the event of an electrical fire. For more on this subject see 'Virgin Electrical Bus'

GLOSSARY

• Aging is the deterioration of wiring insulation with the passage of time. To certain extent aging is a natural process associated with the propensity of most materials to breakdown into their constituent parts over time. (e.g. rust) Most electrical insulation compounds tend to dry out over time, become brittle and crack. Aging of wiring insulation is exacerbated by aircraft vibration causing chaffing (see below) and exposure to a whole raft of chemicals within the aircraft such as hydraulic fluid, engine oil, toilet chemicals, salt spray and moisture etc. Fluorination and other treatments (such as top-coating) may accelerate the aging process.
  
  
  
• Arc tracking is the process by which electrical conductance can occur through and along the insulating coating, rather than just the wire conductor. This is made possible by the formation of carbon along cracks within the insulation material and because carbon is an electrical conductor, once formed the carbon track tends to grow associated with the localised heat that is generated along the track by the electricity leaking through it. The heat generated by the current flow leakage causes a chemical breakdown of the insulating material adjacent to the carbon track, forming more carbon along the track. In other words once initiated the formation of a carbon track becomes self propagating and therefore continues to grow with the passage of time. In other words, once started, arc tracking is capable of self propagation through the virtual instant creation of its own combustion-induced carbon char leading to a massive leakage of electrical current through the carbon track so formed and the damage of adjacent wires in the same wire-bundle. This process is called 'flash-over'. (see next)
  The initiator of arc tracking can be a flaw in the insulation caused by imprint labeling, radial cracking, chafing between wires or contact between a wire conductor and the airframe, hygroscopic absorption of water, salt and other contaminants or an electrical short circuit. It can also be precipitated by undetected shorting damage in inaccessible areas or by use of inappropriate types of insulation in SWAMP areas (severe weather and moisture-prone areas such as wheel-wells).
  NOTE: See also 'Ticking Faults' listed below.
  
  
• Flash-over is the self propagation and catastrophic escalation of an arc tracking event through the instant creation of a major carbon char pathway associated with the heat that is generated during the initial arc track event (i.e. carbon is produced when the insulation material starts to burn) The resulting escalation of the arc track event associated with flashover can be explosive (especially with Kapton wire) and the naked flames can cause damage to adjacent wire-bundles and thermal-acoustic insulation within the airframe. (e.g. Mylar) Vertical wire runs are more susceptible to flash-over (because naked flames naturally rise vertically). However flash-over can also occur horizontally or, less explosively, in a downward vertical sense. Unlike a straight electrical short, the conductor's temperature itself may not rise high enough to trip the circuit protective device (CPD) meaning the arcing phenomena may not necessarily cause a thermal circuit-breaker to trip. The arc tracking phenomenon is based upon the ability of the conductive carbon char to heat adjacent wiring and self-propagate, particularly along a wire bundle more so than an individual wire. Note that the phenomena induced in the presence of significant moisture is called "Wet Arc Propagation" (as against "Dry Arc Propagation"). Wet arcing is more likely to produce the flash-over end-result.
  
  
• Chafing occurs when wires vibrate and rub against each other (or the structure of the aircraft) causing the insulation layer surrounding the wire to be rubbed away exposing the electrical. The vibration causing the chafing is usually the cumulative effect of the high-frequency vibration which naturally occurs in flight associated with aerodynamic and engine vibrations. The tendency for wire to chaff is exacerbated by insufficient tensioning, insufficient offset or the tightening of a wire against an airframe component (especially around corners). Over-tensioning of wires and/or insufficient support intervals can lead to "strumming" of wires (causing them to contact other surfaces). Scraping caused by pulling wire through narrow areas during installation can cause a similar effect to chafing.
  
  
• Cold-flow (creeping of the conductor) is any permanent deformation due to pressure or mechanical force, without the aid of heat softening.
  
  
  
• EMI: Electromagnetic Interference. Wiring that is unshielded is susceptible to strong electromagnetic fields stemming from systems and modules that are natural emitters such as GPS, DME (Distant Measuring Equipment), radios, weather radars, radar altimeters etc (plus cell-phones and Gameboys etc)
  
  
• FBW: Fly By Wire. In conventional aircraft, flight control is actuated by pushrods and cables to hydraulic actuators driving the primary control surfaces (i.e. ailerons, rudders, spoilers, canards, elevons and elevators). In FBW aircraft the physical connections of cables and pushrods are replaced by proportionate computer-generated digitized signals.
  
• Fluid resistance: Resistance to a wide range of commonly used solvents, fluids and lubricants used in aircraft.
  
  
• Hydrolysis: (noun) the chemical reaction of a substance with water, usually resulting in decomposition of the said substance. (Source: Oxford Dictionary)
  
  
  
• Hygroscopic: (adjective): A hygroscopic substance is one that tends to absorb moisture from the air (Source: Oxford Dictionary)
  
  
  
• Notch Propagation: The tendency of a wire insulation to propagate a crack through to the conductor with on going bending cycles. Usual requirement is expressed as an acceptable limit. e.g. The wire shall not propagate a crack to the conductor following a minimum of ten bend cycles of the v-notched area.
  
  
• Outgasses: Some insulation materials are volatile. In many critical aerospace and semiconductor applications, low-outgassing materials must be specified in order to prevent contamination in high vacuum environments. Outgassing occurs when a material is placed into a vacuum (very low atmospheric pressure) environment, subjected to heat, and some of the material's constituents are volatilized (evaporated or "outgassed"). Outgassing is related to conductor temperatures (i.e. load carrying capabilities).
  
  
• Radial cracking: This can occur around a wire's circumference and expose the conductor and cause 'ticking faults'. (see below) Causes of radial cracking can be natural deterioration, insufficient bend radii or damage at installation. Over significant stretches of wire runs, the cause will normally be the degradations due to aging, coupled with top-coat flaking. This latter phenomenon is the natural breakdown of a shellac-like substance applied to protect aromatic polyamide (i.e. Kapton types) in particular from hygroscopic activity. Radial cracking can be initiators of ticking faults.
  
  
• Rated temperature: The maximum temperature at which a given insulation or jacket may be safely maintained during continuous use, without incurring any thermally-induced deterioration. Rated temperature of a wiring insulation/conductor gage may not remain constant for the life of an installation due to the aging process.
  
  
• 'Ticking' faults. This is an intermediate process of wiring insulation breakdown where sufficient conductor exposure (perhaps due to radial cracking) coupled with the early phase of outer carbon charring allows "arcing in miniature" (i.e. "ticking") to occur. Think of it as sparkling along the outer sheath. Once sufficiently advanced, this process will have built up a sufficient carbon char for full-blown self-propagating arc-tracking to occur. If wetted (by say a galley or toilet leak or ramp moisture ingress), the condition may allow an earlier 'flash-over' event.   

   

FOOTNOTES

1. Kapton Arc Tracking and Flashover: According to Dr Armin Bruning of the Lectromechanical Design Company of Dulles, Virginia USA - a company which has been contracted by the US Navy amongst others to investigate Kapton arc tracking - the reason Kapton explodes during an arc tracking event and 'flashover' is because "the arc will cause a temperature of 5000 degrees Celsius ... and in this condition carbon is vaporized and free hydrogen is liberated."
Source: email from Armin M. Bruning Lectromechanical Design Co to Alex Paterson dated 5 May 2001

It would appear that encapsulating Kapton between layers of Teflon [i.e. Teflon - Kapton - Teflon (TKT)] prevents the Kapton layer from drying out and cracking, as well suppressing the production of hydrogen during a short circuit, rendering the Teflon coated Kapton (i.e. TKT) relatively benign from an arc tracking point of view.

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2. Airbus Industries began using a hybrid version of Kapton comprising Kapton coated with Teflon (TK) made by Dupont in some parts of its Fly by Wire aircraft in the late 1990s. However, according to the America's foremost independent aircraft wire expert, Edward Block, this type of wire is "just Kapton with a cosmetic coating of Teflon which is used for marking purposes only and does little to reduce Kapton's propensity to explosively arc track".
However, see note 3 below.

___________________________

3. As of mid 2006 Airbus Industries have started to install their own version of Boeing's TKT in their new Airbus aircraft. This wire is designated Airbus Specification No: EN2267-008. This wire would almost certainly be much safer than bare Kapton, but Airbus Industries refuses to disclose the performance attributes of this wire so it is difficult to determine for certain how safe this wire actually is. See main wire table above for more details about this wire.

___________________________

4. Source: Assertion made by Edward Block in 'Aerospace Testing International' magazine dated June 2009 on page 39.

RELATED WEBSITES:

• International Aviation Safety Association (IASA) - A resource guide to aircraft safety and aircraft wiring.
• 'Aircraft Design Features that Enhance Safety' by Alex Paterson
  

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ABOUT ALEX PATERSON

Alex PATERSON is an Australian airline pilot by profession. He writes articles and advises on issues pertaining to aviation, politics, sociology, the environment, sustainable farming, history, computers, natural health therapies and spirituality.

He can be contacted at:

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