A modern aircraft carries several hundred kilometres of electrical wiring. On a long-haul jet of the A330 or B777 generation, the figure routinely exceeds 150 km of conductors, more than 100 000 connectors, thousands of harnesses and grounding points, all distributed across every zone of the airframe — from electronic bays to engine pylons, cargo holds, wings and empennage. Since 2007 this invisible web has had an official name: EWIS, the Electrical Wiring Interconnection System. Wiring is no longer treated as a loose collection of items but as a fully fledged system, with its own design rules, scheduled inspections and dedicated maintenance procedures.
For a modern Part-145 organisation, mastery of EWIS has become a marker of industrial quality. A mechanic who cannot inspect a harness, identify arc tracking or rebuild a ground point to the standard is exposing the next flight to a risk no one wishes to take. This article offers a technical and regulatory reading of EWIS for B1 and especially B2 LWTR personnel, in the Algerian context and in light of the ANAC Algeria framework.
1. EWIS: a broadened definition of aircraft wiring
Before 2007, aircraft wiring was treated as one sub-assembly among many, scattered across ATA 24 (electrical generation and distribution), ATA 92 (standard wiring) and dozens of system-specific ATA chapters. This dispersion long obscured a simple truth: a wire never exists alone. It is mated to a connector, fixed to a panel, returned to a ground, run through a harness held by clamps, sheathed for protection, kept at a minimum distance from a hydraulic line.
The unified definition adopted by the FAA and then the EASA brings the following elements explicitly under the EWIS umbrella:
- Conductors: single wires, twisted pairs, coaxial cables, shielded wires, optical fibres bundled with service wires.
- Connectors: circular MIL-DTL-38999, modular, grounding connectors, splices, quick-disconnect devices.
- Harnesses: bundles of wires held together, sleeved or not, with their supports, clamps and damping wraps.
- Electrical grounds: return points, ground studs, bonding straps, radio-frequency grounds.
- Protections: circuit breakers (CB), fuses, residual current devices, arc fault circuit interrupters (AFCI), mechanical and thermal sleeves.
- Identification: wire markings, harness tags, wiring diagrams (WD), Wiring Diagram Manual (WDM).
This system view is fundamental. A connection is never just a connector: it is the combination of the wire, the care of the crimp, the cleanliness of the contact, the mechanical retention and the quality of the ground that determines circuit reliability. EWIS failures are rarely spectacular, but their consequences can be.
2. Historical context: TWA 800 and the birth of EWIS regulation
On 17 July 1996, a Boeing 747-131 operating TWA flight 800 broke up in flight over the Atlantic, twelve minutes after take-off from New York-JFK. All 230 occupants perished. The four-year investigation by the US NTSB concluded that the probable cause was an explosion of the centre wing fuel tank, ignited by a source most likely electrical in nature. The retained hypotheses converged on a short circuit in the fuel gauge wiring, whose ageing conductors ran close to the tank walls.
The NTSB report was a regulatory earthquake. For the first time, the global aviation community realised that civil aircraft wiring could age to the point of becoming dangerous, and that traditional maintenance programmes — focused on airframe and engines — did not properly cover the hundreds of kilometres of onboard wiring. In 1998 the FAA launched the ATSRAC programme (Aging Transport Systems Rulemaking Advisory Committee), which in 2007 produced two structuring texts: subpart H of FAR 25 (titled Electrical Wiring Interconnection Systems) and the EAPAS/FTS rule, requiring operators to integrate a dedicated EWIS component into their maintenance programmes.
TWA 800 transformed how the industry sees wiring: no longer a consumable installed once and forgotten, but a structural system subject to ageing and demanding dedicated surveillance.
The investigation also revealed deficient maintenance practices: overloaded harnesses, corroded ground points, undetected insulation degradation that classical visual inspections were missing. Twenty years on, those lessons continue to shape the training of technicians worldwide, including in the Algerian schools delivering Part-66 qualifications.
3. FAR 25.1701 and AC 43-218: the American framework
The American EWIS regulatory framework rests on several complementary texts. The pivot is FAR 25.1701, embedded in subpart H of Federal Aviation Regulations Part 25 (transport aeroplanes). This paragraph defines what an EWIS is, lists design requirements (circuit separation, protection against mechanical aggression, low-flammability materials) and mandates EWIS consideration in every safety analysis of a certified aircraft.
FAR 25.1701 is complemented by paragraphs 25.1703 (system components), 25.1705 (fire safety), 25.1707 (system separation), 25.1709 (safety analysis), 25.1711 (component marking), 25.1713 (fire resistance), 25.1715 (qualification testing), 25.1717 (bypassing and redundancy) and 25.1719 (maintenance accessibility). This network covers the full life cycle of a harness, from design to in-service maintenance.
For maintenance, the FAA published Advisory Circular AC 43-218, titled Aircraft Electrical Wiring Interconnection Systems (EWIS) Best Practices Job Aid. Freely downloadable, it has become the technicians' bible: colour photographs of typical defects, recommended gestures, suggested tooling, wear limits for various wire types. AC 43-218 is not strict regulation, but no serious shop operates without it.
4. EASA CS 25.1701 and AMC 20-21/22/23: the European framework
On the European side, EASA transposed the American philosophy into its CS-25 framework (Certification Specifications for Large Aeroplanes). Paragraph CS 25.1701 mirrors the EWIS definition and imposes equivalent design and analysis requirements. Operationally, three Acceptable Means of Compliance shape European practice:
- AMC 20-21: general requirements for the in-service EWIS integrity programme, applicable to operators. Describes the Enhanced Zonal Analysis Procedure (EZAP), a zonal analysis method used to identify critical inspections to embed in the maintenance programme.
- AMC 20-22: training requirements for personnel involved in EWIS design, installation, inspection and maintenance. Defines five competency levels (Targeted Training Levels 1 to 5) delivered according to role.
- AMC 20-23: EWIS maintenance requirements, a technical complement to the two preceding texts. Details inspections, acceptable repair practices and replacement criteria.
For European Part-145 shops, AMC 20-22 has a direct impact: any mechanic working on a harness or connector must have completed EWIS training of a level matched to their scope. This training — sometimes referred to as EWIS awareness at level 1 and EWIS specialist at levels 4 and 5 — now belongs to the mandatory recurrent training base, alongside Human Factors and Fuel Tank Safety.
5. ANAC Algeria: local adaptation of the EWIS framework
The Algerian regulatory authority, the ANAC, has historically aligned with the EASA framework for transport aircraft maintenance. This regulatory continuity facilitates the mobility of technicians and the mutual recognition of approvals. For EWIS, ANAC adopts the European logic: integration of EWIS inspections into national operators' maintenance programmes, training requirements aligned with the principles of AMC 20-22, and an obligation for approved Part-145 organisations to include EWIS in their Maintenance Organisation Exposition (MOE) and quality procedures.
This local adaptation rests on three pillars. The first is the transposition of the annexes of the Chicago Convention (notably annex 8 on airworthiness) into Algerian aviation law. The second is the ANAC approval of maintenance training organisations and Part-145 shops, which must demonstrate command of the EWIS framework to obtain and retain their approval. The third is continuous oversight by ANAC inspectors, who routinely audit EWIS practices at shops and operators.
For future Algerian shops — and AéroNéo at Tamanrasset is one such project — this ANAC/EASA compliance is an entry ticket to the market. No customer, no lessor and no international airline entrusts an aircraft to a shop that cannot show, with documents, the ability to inspect and maintain EWIS to the state of the art.
6. Degradation modes: why a wire ages
An aircraft wire is designed to last as long as the aircraft itself, typically 25 to 30 years for a commercial transport. In practice, this longevity depends on operating conditions. Four families of degradation dominate in service.
6.1 Mechanical wear
In-flight vibration, ground manoeuvring, repeated opening and closing of panels, and technicians moving through bays during C-checks generate chronic friction between harnesses and their surroundings. Insulation gradually thins, exposing the conductor. Particularly exposed zones include structural edges, hatch surrounds, instrument panel feet and cargo pass-throughs.
6.2 Thermal ageing
Certain zones — engine pylons, electronic bays beneath the cockpit, areas close to air conditioning units — run at elevated, sometimes cyclic temperatures. Insulation, generally polymer-based (PTFE, polyimide, ETFE, PEEK), stiffens, cracks and eventually loses its dielectric properties. On some older generations, Kapton polyimide insulation raised specific issues: sensitive to humidity and prone to propagating arcs.
6.3 Oxidation and corrosion
Ambient humidity, condensation in unconditioned zones (cargo holds, rear fuselage), sea salt for coastal operators, and service fluids (fuel, hydraulic, cabin cleaning) attack metallic contacts. Tinned copper connectors see their contact resistance rise, which translates into localised heating and, in time, intermittent failures that are notoriously difficult to diagnose.
6.4 Contamination
Cabin dust, beverage and food residue under the floor, household fluids, the dropped flashlight, the forgotten tool — everything progressively contaminates harnesses and connectors. In the Algerian Saharan context, fine abrasive dust is a leading factor: it infiltrates everywhere, acts as a corrosion agent in the presence of residual humidity and promotes the formation of conductive paths between wires that should be insulated from each other.
7. EWIS inspections: visual, instrumental and NDT
EWIS inspections come in three families, structured by maintenance manuals and integrity programmes for each aircraft type.
The General Visual Inspection (GVI) is the most common: the technician, with the naked eye and a torch, examines accessible harnesses for signs of friction, discoloration, flattening, sheath splits or loose connectors. The Detailed Inspection (DET) requires a close-up look with magnifier or mirror, sometimes with partial panel removal. The Special Detailed Inspection (SDI) brings in specific tooling: borescope, insulation measurement, thermography.
Instrumentally, two measurements are fundamental: insulation resistance between conductors and between conductor and ground, typically performed at 500 V DC with a megohmmeter, and continuity and bonding resistance measurement on grounding points using a milliohmmeter. Time Domain Reflectometry (TDR) techniques are beginning to spread in the best-equipped shops: they locate a fault on a wire dozens of metres long to within a few centimetres, without physical removal.
The table below summarises the main degradation modes, observable signs and recommended inspection methods, consistent with the principles of AC 43-218 and AMC 20-23.
| Degradation type | Observable sign | Inspection method |
|---|---|---|
| Mechanical wear / chafing | Flattened sheath, thinned insulation, friction marks on structure | GVI then DET with magnifier; gloved-finger sweep to detect thinning |
| Thermal ageing | Stiff, cracked, discoloured insulation (yellowing to browning) | DET with controlled harness flexing; 500 V DC insulation test |
| Contact oxidation | Green tint, white deposits, loss of pin brightness | Borescope inspection of the connector; contact resistance measurement |
| Ground corrosion | Oxidised ground stud, frayed bonding strap | Bonding resistance with milliohmmeter; comparison against WDM values |
| Liquid contamination | Traces of fuel, hydraulic fluid or beverages on harness | DET, cleaning per CMM, insulation test after drying |
| Dust contamination (Sahara) | Sandy deposits in connectors and panels | DET with borescope; dry-air cleaning, post-cleaning visual check |
| Arc tracking | Localised charring, smell, black traces on insulation | Immediate SDI, harness removal, lab analysis if recurrent |
| Marking failure | Illegible or missing label, unidentifiable wire | GVI; remarking per WDM with traceability procedure |
This table does not replace the type-specific procedures, which alone are normative. It serves as a teaching anchor for trainee technicians and pre-inspection briefings.
8. Arc tracking: the feared phenomenon
Arc tracking is the most feared EWIS scenario. It occurs when an insulation defect lets an electrical arc cross between two adjacent conductors, or between a conductor and ground. The arc, fed by the circuit's DC or AC current, vaporises insulation locally, deposits conductive carbon on nearby surfaces, and propagates step by step along the harness. Temperatures at the arc point exceed 2 000 °C, enough to ignite any combustible material in the immediate vicinity.
The mechanism depends on insulation type. Some polymers, including certain historical polyimide formulations, are vulnerable to so-called wet arc tracking: in the presence of humidity or a contaminating fluid, the arc may propagate over several centimetres within milliseconds. Other modern insulations (PTFE composite, ETFE) are designed to extinguish the arc by carbonising in a non-conductive manner: they are termed arc track resistant.
Protection is layered. At circuit level, AFCIs (Arc Fault Circuit Interrupters) detect the characteristic electrical signature of an arc and cut the current within milliseconds, far ahead of a classical thermal breaker. At harness level, physical separation of redundant circuits, sleeving, distance from humidity sources and well-tightened clamps are barriers. At human level, regular inspection remains the best defence: a harness exhibiting local heating, a smell or a black trace must be removed and analysed without waiting for the next scheduled check.
9. The central role of the B2 LWTR in avionics
The certified B2 mechanic (avionics, electrical, instruments) is the front-line responder on EWIS. On recent aircraft, EASA introduced a specific qualification: the B2L, restricted to particular specialisations, and above all the LWTR (Light Aircraft Maintenance Licence — Wiring, Test and Repair) or its equivalent embedded in the standard B2. These qualifications target the strict EWIS scope: connector crimping, harness repair, detailed inspection, insulation measurement, ground stud replacement.
Concretely, the B2 LWTR commands:
- Reading of the Wiring Diagram Manual (WDM) for the aircraft type and the Standard Wiring Practices Manual (SWPM, generally the manufacturer's ATA 20).
- Wire identification and marking per the manufacturer's conventions (Airbus, Boeing, Embraer, ATR, etc.).
- Crimping MIL-DTL or proprietary contacts with the appropriate calibrated dynamometric tools.
- Use of extraction and insertion tools for rear contacts of circular connectors.
- Splice creation per authorised types: crimped, soldered, heat-shrink insulated.
- Installation and inspection of mechanical protection devices: braided sleeves, spiral wrap, heat-shrink sleeves.
- Insulation testing at 500 V DC and interpretation of results against SWPM thresholds.
- Writing EWIS inspection records and entering them into the shop's quality systems.
This toolbox is demanding. A shop that properly trains its B2 LWTR personnel invests in calibrated crimping benches, type-specific tooling chests and continuing training programmes, because techniques evolve with each new connector generation. On modern programmes (A350, B787), the growing use of composite primary structure makes the quality of electrical bonding even more critical: the majority of ground return current now travels through the harnesses themselves.
10. AéroNéo: EWIS in the planned Part-145 programme
The AéroNéo project, in pre-launch at Tamanrasset, places EWIS at the heart of its technical scope. The Part-145 programme targeted at ANAC Algeria will incorporate, from the approval phase onwards, an EWIS capability built around four axes.
The first axis is documentary: a dedicated EWIS procedure embedded in the Maintenance Organisation Exposition (MOE), articulating AMC 20-23 requirements, manufacturer practices (Boeing SWPM, Airbus ABP, Embraer and ATR equivalents) and consolidated lessons learned. The second axis is training: all technical personnel will be qualified at the level appropriate to the AMC 20-22 framework, from level 1 awareness for support staff to level 4 for technical managers and quality inspectors.
The third axis is tooling: calibrated crimping benches, high-precision megohmmeters, milliohmmeters for bonding, borescopes, TDR equipment for fault localisation. The Saharan climate also calls for dust-resistant and thermally robust equipment. The fourth axis is organisation: a quality cell dedicated to EWIS traceability, with before/after photographs, electronic archiving and cross-review between technicians.
This approach is not a luxury but a market-access condition. International customers entrusting aircraft to an Algerian shop assess first its EWIS capability, because it directly reflects the industrial maturity of the organisation. A shop that knows how to inspect and repair wiring to the state of the art also knows how to keep a job card, archive a signature and follow a procedure. It is this quality foundation, more than hangar availability or paint finish, that decides who wins contracts.
EWIS is not an abstract subject. It is rooted in a past tragedy, in hundreds of kilometres of invisible wires, in the patience of a B2 crimping a contact to the right tension, in the rigour of an inspector rereading a ground stud before signing. For the young Algerian aerospace industry, it is a school of technical humility and industrial discipline. It is also a gateway: because mastering EWIS means promising, on every flight, that no arc, no faulty ground and no forgotten harness will break the silent trust between the machine and its crew.
