Wiring Maintenance Practices/Guidelines

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Aircraft Electrical System Safety
Statement of J. Donald Collier Vice President, Engineering, Maintenance & Materiel Air Transport Association of America, Inc. Hearing Before the House Transportation & Infrastructure Committee Aircraft Electrical System Safety October 5, 2000
Madam Chairwoman, thank you for the opportunity to provide comments to the Committee regarding the very important issue of aircraft electrical system safety. On behalf of all of our member airlines, I would like to commend you for holding this hearing and to share with the Committee our efforts to improve upon an already remarkable aviation safety record.

Prior to the tragic experience of Flight 800, FAA and the airline industry had a long and cooperative program of addressing aging aircraft issues, which began in the 1970's. They focused on aircraft structure, since it has long been known that structural components experience fatigue and other degradation associated with age and frequency of usage. There were wiring and other electrical issues as well, but they were considered to be less threatening than structural issues. The routine inspection of wiring was of a nonspecific nature, subject to "general visual inspections" to detect obvious damage, arcing or deterioration. Problems often manifested themselves in the faulty function of components that were at either end of the wiring, and because of the high degree of redundancy in these systems, repairs were made and reported without signaling a potential safety issue.

While faulty function of wires sometimes resulted in the replacement of wire harnesses, the primary issue was maintaining reliability of components in the system rather than reducing the direct threat from electrical arcing because this had not been identified as a focal point of concern. Such was the experience of the FAA and industry in the early years.

Clearly, the Flight 800 accident refocused attention to this issue. Shortly after the accident, ATA took the lead in working with FAA to address wiring concerns brought forward in the investigation. In 1998, ATA formed the Aging Systems Task Force, a forum in which airlines, FAA, manufacturers and other aviation parties evaluated and responded to aging wiring issues. The ASTF ultimately became an extension of the FAA Aging Transport Systems Regulatory Advisory Committee (ATSRAC).

One of the first products of ASTF was the publication of guidelines containing the best practices of industry for maintenance of wiring. The guidelines were published July 31, 1998 as ATA Specification No. 117, "Wiring Maintenance Practices/Guidelines," and made available to all interested parties. The purpose of this guideline was to capture in a single location valuable information about recommended electrical practices and procedures from various documents used by airlines, equipment manufacturers, professional organizations and the FAA. Subsequently, a training video was produced and distributed by ATA, capturing the key elements of Spec 117.

Spec 117 addresses the major wiring maintenance topics of:

I. Causes of Wiring Degradation
II. Inspection Practices, and
III. Wiring Maintenance Practices.

Causes of wiring degradation include vibration, moisture, chemical contamination, heat, indirect damage, and side effects of aircraft maintenance (metal shavings, etc.). The guidelines point out the importance of checking wire clamping, connectors, terminations, conduits and grounding points. It identifies the sites where the causation of degradation is most severe - wing leading edges, engine pylons, Auxiliary Power Units, landing gear wheel wells, under galleys and lavatories, etc. And it identifies good practices for applying protections against chafing, moisture, chemical contamination and other causes of degradation.

Spec 117 was published for use by airlines and repair stations to guide their review of current practices and modification as needed. It has been widely distributed and implemented throughout the airline industry. While the vast majority of the practices set forth in Spec 117 were contained in airline maintenance programs prior to its creation, the Spec provided a basis for improved focus for many air carriers and repair stations.

ASTF did not stop there. The Task Force also designed a non-intrusive inspection program for aging aircraft whereby teams performed detailed visual examinations of in-service or recently retired airplanes for evidence of phenomena related to aging wiring. From late 1998 through 1999, the teams performed these inspections on A300, B727, B737, B747, DC8, DC9, DC10 and L1011 airplanes that were voluntarily made available by ATA members and other airlines. These airplanes were defined as aging aircraft in accordance with FAA's pre-existing aging aircraft program. In all, 81 airplanes were inspected under the inspection program. Results were published in August 2000. It is our understanding that representatives of the FAA ATSRAC will address the findings of this inspection program before the Committee.

The inspection findings were ordered into three categories. In the top priority category, there were no findings that indicated a need to take immediate fleet action to address an airworthiness concern. A number of findings that either were replicated on several aircraft or were deemed to have a potential over time for impairing airworthiness are being examined further by the manufacturer for possible service instructions, service bulletins or other action. Most of the findings required no follow-up at all. Moreover, the experience of performing the inspections enabled ATA to improve the guidance in Spec 117, which has since been revised.

Airlines who made airplanes available for non-destructive evaluation provided labor of approximately 100 man-hours per airplane to support the inspections. Including the efforts of the inspection teams - FAA, manufacturer and airline members - and the subsequent analysis of results, the total effort exceeded 50,000 man-hours.

ASTF also designed a plan for intrusive inspections of six airplanes, i.e., destructive testing of wiring from airplanes that have been recently retired. This effort is now being conducted under the auspices of ATSRAC and under the leadership of the FAA Technical Center. Retired aircraft needed for the performance of this program have been donated by ATA members and other airlines. While fewer airplanes will be involved, the effort required for each will be twice that of the non-intrusive inspections.

ASTF conceived a plan for reviewing the past service history of airplanes, including all previous service bulletins that were related to aging wiring. Such bulletins were to be evaluated for a possible upgrade in importance and, depending on their nature, possible recommendation for treatment by FAA as Airworthiness Directives. This effort continues today under the aegis of the ATSRAC.

Airlines on their own initiative have taken numerous steps beyond the work of ASTF and ATSRAC. To name a few, airlines have:

1. stimulated tooling manufacturers to develop new tools to aid in the detection of wiring problems;
2. encouraged the development of wireless systems for aircraft such as wireless Fuel Quantity Indicating Systems;
3. participated with the Fuel Systems Safety Leadership Team in the voluntary inspection of fuel tanks in B747s and other aircraft types for electrical problems (over 900 airplanes inspected under this program);
4. participated in the Aircraft Wire and Inert Gas Generation meetings, and shared experiences with other airlines at conference dealing with Nondestructive Testing Technology;
5. revised their maintenance programs to require more specific inspection criteria for wires;
6. provided additional training based on Spec 117 for engineering, inspection and maintenance personnel;
7. added specific inspection instructions for fuel tank bonding jumpers;
8. participated with FAA in the on-going development of arc-fault circuit breaker technology;
9. emphasized root-cause analysis of all smoke/fire/electrical arcing incidents;
10. enhanced inspection and maintenance programs as a result of root-cause analyses;
11. emphasized protection of wiring during sheet metal repairs, corrosion control compound application, and washing;
12. focused on maintaining adequate wire bend radius, and inspections for environmental damage, chafing, bare wires, dust buildup, and arc damage;
13. replaced main wheel well wiring bundles on certain airplanes to incorporate improved conduit protection;
14. accelerated compliance with certain service bulletins and airworthiness directives; and
15. added specific inspections for the wiring located in the tail compartment of certain airplanes to detect evidence of brittleness or other aging symptoms.

This list is by no means exhaustive, but is illustrative of the depth and breadth of attention that airlines have applied - and will continue to apply - to aging wiring concerns.

The efforts and results described above will add extra safety margins to the air carrier fleet, a fleet that the record shows is already incredibly safe. The cooperative efforts of FAA, airframe and component manufacturers, operators and others were critical to this success and each should be lauded.

We are more than willing to provide any other information needed to support the Committee's oversight of this critical air safety issue.



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ATA Spec 117:

Wiring Maintenance Practices/Guidelines

Click ATA Specification 117 to download entire Spec in Rich Text Format.

ATA Specification 117
Wiring Maintenance Practices/Guidelines

Revision 2001.1

Air Transport Association of America, Inc.
1301 Pennsylvania Ave., N.W., Suite 1100
Washington, D.C. 20004-1707

Copyright 2000 by Air Transport Association of America, Inc. All rights reserved. No part of this document may be reproduced or transmitted by any means, electronic or mechanical, including photocopying and recording, or by any information storage or retrieval system, except as may be expressly permitted in writing by the publisher.

Important Information About This Document

Read Before Using This Document

This document contains recommended specifications that have been developed for the covered topics. ATA does not mandate their use. You must decide whether or not to use the recommendations in this document. You may choose to use them in whole, in part, or not at all.

There may be practices, standards and / or regulatory requirements applicable to your operations that exceed the recommendations in this document. You are solely responsible for determining if such practices, standards or requirements exist and whether they apply to your activities, and for complying with those that are applicable. Such practices, standards and requirements can change significantly over time.

ATA does not guarantee, promise or warrant that the specifications in this document will meet the needs of your operations. This is a determination that you must make and for which ATA is not responsible.

For Additional Information

For more information or to order additional publications, refer to the ATA Publications Catalog, the website at www.airlines.org, e-mail pubs@airlines.org or call the ATA Distribution Center at:

1-800-497-3326 (U.S. & Canada)

For Technical Information and Change Submissions

For technical information or to recommend an alteration or amendment to this specification, please submit the recommendation and any supporting documentation to ATA:

E-mail: pubs@airlines.org
Fax: 1-202-626-4181


Release History

Revision 2001.1: July 2000

Revision 2000.1: January 2000

Issued July 31, 1998

Revision 2001.1 (July 2000)

Location Description of Change
Chapter 3 Editorial.
Added Cleaning to "Causes of Wiring Degradation."
Chapter 4 Added Splices to "Wiring Installation Types" in 4-1.
Expanded Primary Inspection Locations in 4-2
Chapter 5 Editorial.
Enhanced protection of wiring from contamination and debris.
Enhanced the concept of "clean-as-you-go."
Corrected edge distance measurement in 5-1., and added metric version.
Added Section 5-9, "Cleaning"

Table of Contents

Chapter 1. Background
Chapter 2. Scope
Chapter 3. Causes of Wiring Degradation
Chapter 4. Inspection Practices
Chapter 4-1. Wiring Installation Types
Chapter 4-2. Primary Inspection Locations
Chapter 5. Wiring Maintenance Practices
Chapter 5-1. Protection Against Chafing
Chapter 5-2. Protection Against High Temperature
Chapter 5-3. Protection Against Solvents and Fluids
Chapter 5-4. Engine and APU Wire Harnesses
Chapter 5-5. Protection of Wires in the Wheel Well Area
Chapter 5-6. Routing Precautions
Chapter 5-7. Connectors
Chapter 5-8. Conduits
Chapter 5-9. Cleaning
Annex 1. Additional Reading

Chapter 1. Background

The Federal Aviation Administration (FAA) is developing an Aging Non-Structural Systems Plan in response to the White House Commission on Aviation Safety and Security (WHCSS) recommendations regarding aging non-structural systems. These recommendations state: "In cooperation with airlines and manufacturers, the FAA's Aging Aircraft program should be expanded to cover non-structural systems." The Commission was concerned that existing procedures, directives, quality assurance, and inspections may not be sufficient to prevent safety related problem, caused by the corrosive and deteriorating effects of non-structural components of commercial aircraft as they age. One area of special concern to the Commission was airplane wiring.

While preliminary industry findings indicate that wiring degradation is minimized when properly installed, it has been shown that vibration, moisture, contamination, etc. can negatively impact the condition of wiring. Consequently, inspections should focus on those areas where these environmental conditions exist.

Maintenance activity can vary greatly from aircraft to aircraft. The disruptive effects of maintenance activity can be more random than the environmental factors that can lead to wire degradation. Wiring should be viewed as an aircraft system, and maintenance practices should focus on maintaining the integrity of the wiring system.

FAA investigation results are similar to the preliminary findings from industry research: wire degradation seems to be principally caused by installation, environmental, and maintenance factors. Some specific findings and concerns raised during the FAA's recent wiring review are: drill shavings and other metal debris in bundles (with cut insulation); lint accumulations; chemicals of various types on wiring (corrosion-inhibitor, paint, hydraulic fluid, oil, grease, soft drinks, coffee, lavatory fluid, etc.); aging and deterioration of materials (cracks in wire insulation, clamp cushions crumbling, crumbled potting in pump connectors, cracked o-rings, etc.); extensive nicks, cuts, and chafes; workmanship issues; and compromised wiring segregation.

The FAA is composing a blueprint to address aging non-structural systems. The blueprint will form the basis of a joint FAA/industry plan that will be modeled after the FAA/industry aging aircraft work. This plan is viewed as a long-term initiative. It is ATA's intent that this document provide guidelines to be shared among industry in the short term for the improvement and formulation of wiring practices.

Return to Table of Contents

Chapter 2. Scope

This information is general guidance. Special inspections should be conducted as deemed appropriate by each operator, based on airplane maintenance experience. Any discrepancies found should be repaired per the aircraft maintenance manuals. Operators are encouraged to incorporate the following guidelines as a part of their current wiring maintenance practices.

These guidelines are a compilation of manufacturer investigations and operator experience through continuing analysis and surveillance programs. This guidance is not considered all-inclusive. Inspector/maintenance technician training requirements have been specifically omitted.

Return to Table of Contents

Chapter 3. Causes of Wiring Degradation

The following items are considered principal causes of wiring degradation and should be used to help focus maintenance programs:

Vibration - High vibration areas tend to accelerate degradation over time, resulting in "chattering" contacts and intermittent symptoms. High vibration can also cause tie-wraps, or string-ties to damage insulation. In addition, high vibration will exacerbate any existing problem with wire insulation cracking.

Moisture - High moisture areas generally accelerate corrosion of terminals, pins, sockets, and conductors. It should be noted that wiring installed in clean, dry areas with moderate temperatures appears to hold up well.

Maintenance - Maintenance activities, if done improperly, may contribute to long term problems and wiring degradation. Repairs made to minimum airworthiness standards may have limited durability and should be evaluated to ascertain if rework may be necessary. Repairs that conform to manufacturers recommended maintenance practices are generally considered permanent and should not require rework.

Metal shavings and debris have been discovered on wire bundles after maintenance or repairs have been conducted. As a general rule, wiring that is undisturbed will have less degradation than wiring that is reworked. As wiring and components become more brittle with age, this effect becomes more pronounced.

Indirect Damage - Events such as pneumatic duct ruptures can cause damage that, while not initially evident, can later cause wiring problems. When such an event has occurred, surrounding wire should be carefully inspected to ensure no damage is evident.

Chemical Contamination - Chemicals such as hydraulic fluid, battery electrolytes, fuel, corrosion inhibiting compounds, waste system chemicals, cleaning agents, deicing fluids, paint, and soft drinks can contribute to degradation of wiring. Wiring in the vicinity of these chemicals should be inspected for damage or degradation. Recommended original equipment manufacturer cleaning instructions should be followed.

Hydraulic fluids, for example, require special consideration. Hydraulic fluid is very damaging to connector grommet and wire bundle clamps, leading to indirect damage, such as arcing and chafing. Wiring that may have been exposed to hydraulic fluid should be given special attention during wiring inspections.

Heat - Wiring exposed to high heat can accelerate degradation, insulation dryness, and cracking. Direct contact with a high heat source can quickly damage insulation. Even low levels of heat can degrade wiring over long periods of time. This type of degradation is sometimes seen on engines, in galleys, and behind lights.

Cleaning - Overzealous cleaning and use of inappropriate solvents can cause wiring degradation.

Return to Table of Contents

Chapter 4. Inspection Practices

This section provides inspection guidelines and is divided into installation issues and primary inspection considerations. The information is a compilation of ongoing industry research and analysis.

Return to Table of Contents

4-1. Wiring Installation Types

The following are types of installations that merit special attention during wiring inspections:

Clamping points - Wire chafing is aggravated by damaged clamps, clamp cushion migration, or improper clamp installations.

Connectors - Worn environmental seals, loose connectors, missing seal plugs, missing dummy contacts, or lack of strain relief on connector grommets can compromise connector integrity and allow contamination to enter the connector, leading to corrosion or grommet degradation. Drip loops should be maintained when connectors are below the level of the harness and tight bends at connectors should be avoided or corrected.

Terminations - Terminations, such as terminal lugs and terminal blocks, are susceptible to mechanical damage, corrosion, heat damage and chemical contamination. Also, the build up and nut torque on large-gauge wire studs is critical to their performance.

Backshells - Wires may break at backshells, due to excessive flexing, lack of strain relief, or improper build-up. Loss of backshell bonding may also occur due to these and other factors.

Sleeving and Conduits - Damage to sleeving and conduits, if not corrected, will often lead to wire damage.

Grounding Points - Grounding points should be checked for security (i.e. tightness), condition of the termination, cleanliness, and corrosion. Any grounding points that are corroded or have lost their protective coating should be repaired.

Splices - Both sealed and non-sealed splices are susceptible to vibration, mechanical damage, corrosion, heat damage, chemical contamination, and environmental deterioration.

Return to Table of Contents

4-2. Primary Inspection Locations

The following locations should receive special attention:

Wings - The wing leading and trailing edges are areas that experience difficult environments for wiring installations. The wing leading and trailing edge wiring is exposed on some aircraft models whenever the flaps or slats are extended. Other potential damage sources include slat torque shafts and bleed air ducts.

Engine, Pylon, and Nacelle Area - These areas experience high vibration, heat, frequent maintenance, and are susceptible to chemical contamination.

APU - Like the engine/nacelle area, the APU is susceptible to high vibration, heat, frequent maintenance, and chemical contamination.

Landing Gear and Wheel Wells - This area is exposed to severe external environmental conditions in addition to vibration and chemical contamination.

Electrical Panels and LRUs - Panel wiring is particularly prone to broken wires and damaged insulation when these high density areas are disturbed during troubleshooting activities, major modifications, and refurbishment. One repair facility has found that wire damage was minimized by tying wiring to wooden dowels. This reduced wire disturbance during modification. It is also recommended to remove entire disconnect brackets, when possible, instead of removing individual receptacles.

Batteries - Wires in the vicinity of all aircraft batteries should be inspected for corrosion and discoloration. Discolored wires should be inspected for serviceability.

Power Feeders - Operators may find it advantageous to inspect splices and terminations for signs of overheating and security. If any signs of overheating are seen, the splice or termination should be replaced. This applies to galley power feeders, in addition to the main and APU generator power feeders. The desirability of periodically retorquing power feeder terminations should be evaluated.

Under Galleys and Lavatories - Areas under the galleys, lavatories and other liquid containers are particularly susceptible to contamination from coffee, food, water, soft drinks and lavatory fluids, etc. Fluid drain provisions should be periodically inspected and repaired as necessary.

Cargo Bay/Underfloor - Damage to wiring in the cargo bay underfloor can occur due to maintenance activities in the area.

Surfaces, Controls, and Doors - Moving or bending harnesses should be inspected at these locations.

Access Panels - Harnesses near access panels may receive accidental damage and should have special emphasis inspections.

Under Doors - Areas under cargo, passenger and service entry doors are susceptible to fluid ingress from rain, snow and liquid spills. Fluid drain provisions and floor panel sealing should be periodically inspected and repaired as necessary.

Under Cockpit Sliding Windows - Areas under cockpit sliding windows are susceptible to water ingress from rain and snow. Fluid drain provisions should be periodically inspected and repaired.

Return to Table of Contents

Chapter 5. Wiring Maintenance Practices

All wiring should be maintained so that it is mechanically and electrically sound and neat in appearance. It is imperative to prevent or significantly reduce potential contamination or debris from coming into contact with the wiring and components during all maintenance, repairs and modifications. This begins with always being aware of potential wiring contamination, and remembering to install appropriate protection (e.g., plastic sheeting), as necessary, to cover avionics/electrical wiring and components. Furthermore, a "clean-as-you-go" attitude helps to maintain the integrity of the installation. In other words, care should be taken to protect wire bundles and connectors during work, and to ensure that all shavings, debris and contamination are cleaned up after work is completed.

Following maintenance, care should be taken to restore routing in accordance with manufacturers' documentation. The wiring must be adequately supported throughout its length. A sufficient number of supports must be provided to prevent undue vibration of the unsupported lengths. All wires and wire groups should be routed and installed to protect them from:

  • Chafing or abrasion
  • High temperature
  • Being used as handholds
  • Damage by personnel moving within the aircraft
  • Damage from cargo stowage or shifting
  • Damage from battery acid fumes, spray, or spillage
  • Damage from solvents and fluids.

Specific routing and installation procedures are described in the aircraft maintenance/wiring diagram manuals. In general terms, the following items can be considered guidelines when conducting wiring maintenance:

Return to Table of Contents

5-1. Protection Against Chafing

Wires and wire groups should be protected against chafing or abrasion in those locations where contact with sharp surfaces or other wires would damage the insulation. Cable clamps should be used to support wire bundles and maintain spacing at each hole through a bulkhead. If wires come closer than 3/8 inch (10mm) to the edge of the hole, a suitable grommet should be used in the hole

Sometimes it is also necessary to cut nylon or rubber grommets to facilitate installation. In these instances, after insertion, the grommet can be secured in place with general-purpose cement. The cut should be at the top of the hole, and made at an angle of 45 degrees to the axis of the wire bundle hole.

Return to Table of Contents

5-2. Protection Against High Temperature

To prevent insulation deterioration, wires should be kept separate from high-temperature equipment, such as resistors, exhaust stacks, or pneumatic ducts. The amount of separation is normally specified by engineering drawings. Some wires must invariably be run through hot areas. These wires must be insulated with high-temperature material. A low-temperature insulation wire should never be used to replace a high-temperature insulation wire.

Many coaxial cables have soft plastic insulation, such as polyethylene, which is especially subject to deformation and deterioration at elevated temperatures. All high-temperature areas should be avoided when installing cables insulated with plastic or polyethylene.

Return to Table of Contents

5-3. Protection Against Solvents and Fluids

One frequently encountered hindrance to inspections is dirt and grime. Consult the manufacturer's maintenance instructions for recommendation on materials suitable for cleaning electrical connectors and wires. For wire inspections, a soft cloth, such as a cotton glove, can be used to clean individual wires. With any cleaning process, care should be taken not to remove wire markings and ID tape. In addition, airplanes are often pressure washed with a general purpose detergent. Moderate pressure and a general purpose detergent are not harmful to wiring, but water under high pressure can penetrate components such as connectors and splices. Moisture penetration into components tends to increase with elevated water temperatures.

Return to Table of Contents

5-4. Engine and APU Wire Harnesses

Consideration should be given to the refurbishment of engine and APU wire harnesses during engine and APU maintenance visits due to the harsh environment.

Return to Table of Contents

5-5. Protection of Wires in the Wheel Well Area

Typically, wire bundles in this area should be mechanically protected. These wires and their protective devices should be inspected carefully at frequent intervals. There should be no strain on attachments when parts are fully extended, slack should not be excessive.

Return to Table of Contents

5-6. Routing Precautions

When wiring must be routed parallel to combustible fluid or oxygen lines for short distances, as much fixed separation as possible should be maintained. Specific separation standards should be available in manufacturer documentation. However, when such information is unavailable, a six-inch minimum separation may be used as a guideline, and no wire should be routed nearer than 1/2 inch to a plumbing line. The wires should be on the level with, or above, the plumbing lines. Clamps should be spaced so that if a wire is broken at a clamp, it will not contact the line. When a specified separation is not possible, both the wire bundle and the plumbing line can be clamped to the same structure to prevent any relative motion. A wire or wire bundle should not be supported from a plumbing line that carries flammable fluids or oxygen.

Wiring should be routed to maintain a manufacturer recommended minimum clearance from control cables. When a manufacturer-specified clearance is not given, coordinate with the Original Equipment Manufacturer (OEM).

Return to Table of Contents

5-7. Connectors

A connector should be disconnected from a receptacle in the following manner:

  1. Use connector pliers to loosen coupling rings, which are too tight to be loosened by hand.
  2. Alternately pull on the plug body and unscrew the coupling ring until the connector is separated.
  3. Protect disconnected plugs and receptacles to keep contamination from entering and causing faults.
  4. Do not use excessive force, and do not pull on attached wires.

NOTE: When reconnecting, special care should be taken to ensure the connector body is fully seated, the jam nut is fully secured, and no tension is on the lines.

Return to Table of Contents

5-8. Conduits

Conduits are used in aircraft installation for protection of wires and cables. Conduits are available in metallic and nonmetallic material, both in rigid and flexible form. When selecting conduit size, a general recommendation is to select the inside diameter of the conduit to be about 25% larger than the maximum diameter of the conductor bundle.

Conduits are vulnerable to abrasion at the ends. Suitable fittings are affixed to the conduit ends in such a manner that a smooth surface comes in contact with the conductor within the conduit. When fittings are not used, the conduit ends should be flared to prevent wire insulation damage. The conduit should be supported by clamps along its run.

Many of the common conduit problems can be avoided by proper attention to the following details:

  1. Do not use a conduit as a handhold or footstep.
  2. Ensure drain holes are provided at the lowest point in a conduit run and are clear. Drilling burrs should be carefully removed from the drain holes.
  3. Ensure that the conduit is supported to prevent chafing against the structure and to avoid stressing its end fittings.

Damaged conduit sections should be repaired to prevent damage to the wires or wire bundle. The minimum acceptable tube bend radii for a rigid conduit as prescribed by the manufacturer's instructions should be followed. Kinked or wrinkled bends in a rigid conduit are normally not acceptable. Transparent adhesive tape is recommended when cutting flexible tubing with a hacksaw to minimize fraying of the braid.

Return to Table of Contents

5-9. Cleaning

Care must be taken whenever wiring is being cleaned, especially as the aircraft and its wiring age. In general, wire insulation may become brittle, so displacement or moving of wiring during cleaning must be kept to the absolute minimum. Careful identification of the most appropriate cleaning methodology is very important. Vacuuming, perhaps in combination with light sweeping of wiring and wire bundles with soft brushes, to remove dirt and debris may be preferred. Additionally, significant damage can be done to wire insulation and other electrical system components with the inappropriate use of cleaning solvents.

Return to Table of Contents

Annex 1. Additional Readings

[AC 43.13-1B] FAA Advisory Circular (AC) 43.13-1B, Acceptable Methods, Techniques, and Practices, Aircraft Inspection and Repair, Chapter 11. Electrical Systems, Federal Aviation Administration (http://www.faa.gov). Available for viewing online at http://www.faa.gov/avr/afs/300/pdf/1a-cover.pdf
[AC 65-15A] FAA Advisory Circular (AC) 65-15A, Airframe & Powerplant Mechanics Airframe Handbook, Chapter 11. Aircraft Electrical Systems Federal Aviation Administration (http://www.faa.gov). Index of ACs online at http://www.faa.gov/abc/ac-chklst/actoc.htm
[747-SL-20-048] Boeing 747 Service Letter 747-SL-20-048, Inspection of Wiring on High Time Airplanes, The Boeing Company, Technical Library, PO Box 3707, Seattle, WA, USA 98124
[D6-54446] Document D6-54446 Chapter 20, Standard Wiring Practices Manual, The Boeing Company, Technical Library, PO Box 3707, Seattle, WA, USA 98124
[FAST article number 14] FAST the Airbus Technical Digest from Airbus Industrie, FAST 14, February 1993, article, Ageing - The electrical connection, Airbus Industrie, 1 rond point Maurice Belloute, 31707 BLANGNAC Cedex, France, Attn: The Editor FAST AI/CM-S, E-mail: fast.digest@airbus.fr, http://www.airbus.com
[FAST article number 18] FAST the Airbus Technical Digest from Airbus Industrie, FAST 18, June 1995,article, Ageing-The electrical connection - Part 2, Airbus Industrie, 1 rond point Maurice Belloute, 31707 BLANGNAC Cedex, France, Attn: The Editor FAST AI/CM-S, E-mail: fast.digest@airbus.fr, http://www.airbus.com
[WDM - Chapter 20] Chapter 20, Standard Practices - Wiring Diagram Manual, Airbus Industries, 1 rond point Maurice Belloute, 31707 BLANGNAC Cedex, France, Attn: The Editor FAST AI/CM-S, E-mail: fast.digest@airbus.fr, http://www.airbus.com

Return to Table of Contents

6/14/2001 11:29:00 AM

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