Electrical Wiring Interconnection Systems - GMF AeroAsiaintra-02.gmf-aeroasia.co.id/e-learning/assets/files/material/... · The Inhouse Production Training has been designed for maintenance

Manual No.: COT-0037 For Training Purpose Only Date of Issue : January 17, 2014

Training Handbook

Electrical Wiring Interconnection Systems


Manual No.: COT – 0037 For Training Purpose Only Issue: January 17, 2014 Page 1

Volume I

Training Development & Administrative Guide



Training Development & Administrative Guide

Table of Contents

Page

Foreword 3

Training objective 4

Qualification Criteria to attend the Training 5

Introduction to Volume I & II 6

Method of Assessment 7

Course Curriculum 8



FOREWORD

This training Handbook has been designed as a part of GMF AEROASIA requirement to meet the Domestic, FAA AC 120-94 and Foreign Authority Regulation. Conducting Inhouse Production Training is a part of continues airworthiness for Electrical & Avionics maintenance staff (Supervisor, aircraft maintenance engineer and technician) to upgrade and compliance with regulations. The Inhouse Production Training has been designed for maintenance unit in Line maintenance activity. The TL Production Training prepared and designed training Handbook Standard Practice for Electrical & Avionics materials adopted from Boeing Alteon training and other reference books . This training Handbook is for training purpose only, but subject to be up graded to keep current information.



Training Objective

This course satisfies for FAA Advisory Circular 120-94 / AMC 20-22. Upon completion of the course, the students will be able to: a) Know the safe handling of aero-plane electrical systems, Line Replaceable Units (LRU), tooling, troubleshooting procedures

and electrical measurement

b) Know different types of inspections, human factors in inspections, zonal areas and typical damages

c) Know the contamination sources, materials, cleaning and protection procedures

d) Know the correct ID of different wire types, their inspection criteria and damages tolerance, repair and preventative maintenance

Duration Approximately 16 training hours.



Qualification Criteria to attend the Training

The course delegates should have previously attended and passed in basic aircraft airframe & powerplant course and have several years experience in aircraft maintenance and inspection.



Introduction To Volume I and II

Volume I : Provides the introduction /overview of training development and administration guide of the course including the method of assessment in which GMF Training Department is committed with time table of this training

Volume II : Provides necessary information to successfully complete this course.

Module A : General EWIS Practices (parts) Module C : Inspection (parts) Module D : Housekeeping Module E : Wire (parts)



Method of Assessment

The course delegates will be graded base on assessment of written or oral examination. In the situation that a delegate is either not understanding the subject, or not participating adequately, he/she shall made aware of the shortfall in performance and, if appropriated, be provided with additional coaching outside the formal course hours. Absence of more than 10% of the planned duration of the course shall be cause for failing of the course. In the last day of this course, the course delegates will do practical training and continued by written or oral examination The written or oral examination will be in English or Bahasa Indonesia To pass the examination the delegates must obtain at least 70 marks.



Course curriculum of Volume II

No. Subject Page

01 Part A -General Wiring System Practices

Safety Practices 3 Electrostatic Discharge Sensitive (ESDS) Device Handling and Protection 15

LRU Replacement General Practices 22

02 Part C -Inspection

Important Information 2

Special lnspections 5 Criteria and Standards 5 Zonal Areas of Inspection 6 Wiring System Damage 35 Human Factors in Inspection 44

03 Part D -Housekeeping

Important Information 3 Contamination Sources 4 Contamination Protection Planning 25 Protection During Airplane Maintenance and Repair 30 Cleaning Processes 35



04 Part E -Wire

Typical Damage and Areas Found Electrical Bonding and Grounds 3 15

05 Examination

Part A Electrical Wiring Interconnection Systems


This module introduces and explains: 1. Safety practices; 2. Electrostatic discharge sensitive (ESDS) device handling and protection; 3. LRU Replacement general practices



General Information

In order to begin training on aircraft wiring systems, a foundation of safety and procedure practices must be understood. This Module explains the areas associated with wiring systems maintenance. Safety is the highest priority of any maintenance activity. This Module explains the principles of first aid as it relates to airplane wiring systems, as well as, human factors that can present potential dangers. Electrostatic discharge can be catastrophic to the operation of airplane wiring systems. This Module explains the causes of static electricity and how technicians can protect wire system components from its damaging effects. Tools and equipment used in maintenance of airplane wiring systems are specialized and technicians must be familiar with their operations. This Module shows associated tools and equipment and identifies their uses. Calibration and certification of wiring instruments and tools must be performed before appropriate maintenance procedures can be done. This Module explains the inspection, requirements, and protection of such equipment.

Troubleshooting is an essential part of maintenance. This Module explains the procedures, charts, and measurements used to isolate faults in order to conduct airplane wiring system maintenance. Measurement and repair procedures shows detailed methods of electrical measurement of circuits, cards, connectors and harnesses. When replacing LRU's, it is important that they are unserviceable first. No Fault Found concerns are discussed as are possible procedures to reduce them. CAT II & Ill landing considerations and LRU concerns are also discussed.



1. Safety Practices

In this section, students will learn about general safety procedures and practices as they relate to electricity, shock hazards, emergencies, maintenance, and human factors.



General Safety Awareness Most accidents are caused by one of only two factors - unsafe acts or practices and/or unsafe conditions. In fact, studies show that nine out of ten accidents are the result of unsafe acts or negligence. Most of us tend to rationalize the risk of getting injured. We think to ourselves that we have done this job many times this way and nothing has happened yet; so nothing bad will happen to us today. We understand there is a potential danger but think that the risk is low because we have not been injured in the past. We even tend to think of ourselves as very safety conscious. We know the right way to do the job, we've been trained correctly, and we realize that it is hazardous to do it this way, but what we're really thinking to ourselves is "It won't happen to me". Most of us are often meticulous about following safe work practices, but because the job will "only take a minute" we use an unsafe method or tool. For example, not putting on our safety glasses because the job will only take a minute, or not locking out a machine because an adjustment will only take a second. "Besides, I'll be done with the job long before the time it takes to go get the proper safety equipment". We usually think about it just before we do something a little unsafe, or maybe even very unsafe.

We know better, we've been trained on the safe way to do it, but we take that small chance because we think nothing will happen this time. In effect we are saying "I know this could result in an injury, but I'm willing to take the chance - besides it can't happen to me". Maybe it's human nature to think we are invincible, to think that accidents happen to others, but they can happen to us too. Only you can decide to do the job safely and correctly. To provide safe working, every technician should observe the following rules: 1. Know the potential hazards and appropriate

safety precautions before beginning work. Ask and be able to answer the following questions: What are the hazards? What are the worst things that could

happen? What do I need to do to be prepared? What work practices, facilities or personal

protective equipment are needed to minimize the risk?

2. Know the location and how to use emergency equipment, including safety showers and eyewash stations.

3. Familiarize yourself with the emergency response procedures, facility alarms and evacuation routes.

4. Know the types of personal protective equipment available and how to use them for each procedure.

Be alert to unsafe conditions and actions and bring them to the attention of your supervisor immediately so that corrections can be made as soon as possible 1. Avoid distracting or startling other workers. 2. Do not engage in or allow practical jokes or

horseplay. 3. Use maintenance equipment only for its

designated purpose. 4. Do not allow visitors, including children and

pets, in maintenance areas while work is in progress.

5. Smoke in the designated smoking areas

only.

6. Confine long hair and loose clothing in the work area. Wear shoes at all times. Opened-toed shoes or sandals a re not authorized.

7 Keep work areas clean and free from

obstruction. Clean your area immediately. 8. Do not block access to exits, emergency

equipment, controls, electrical panels, etc. 9. Avoid working alone whenever possible. 10. Remain alert and aware at all times.



Electrical Shock and Hazards (current is lethal) The major hazards associated with electricity are electrical shock and fire. Electrical shock occurs when the body becomes part of the electric circuit. This happens when the individual comes in contact with: Both wires of an electrical circuit. One wire of an energized circuit and the ground; or A metallic part that has become energized by

contact with an electrical conductor. The severity and effects of an electrical shock depend on the pathway through the body, the amount of current, the length of time of the exposure, and whether the skin is wet or dry. Water is a great conductor of electricity, allowing current to flow more easily in wet conditions and through wet skin. Symptoms range from a slight tingle to severe burns or even cardiac arrest. Current flowing through the highly sensitive central nervous system can, under certain conditions, cause serious injury or death. Electrical Fire Hazards Electrical fires pose an enormous hazard to personnel and equipment. Risk of fire related damage and injury can be minimized by taking precautions to make your workplace safer. Check and maintain all equipment and tools on a

regular basis. Be aware of all devices that produce sparks,

including motor driven appliances and tools. If a fire breaks out, stay calm, and follow applicable fire fighting/ evacuation procedures.

Current The type of current involved alternating current (AC) or direct current (DC) is very important. Low voltage, up to 40 volts of direct current circuits, do not normally represent a hazard to human life. However, even at low voltage, alternating current circuits can be dangerous and present a lethal threat. Both the magnitude and the path of the current flowing through the body are of primary importance. When the path of the current is hand to hand or foot-to-foot, vital organs (brain, heart, lungs, spinal cord) are affected, possibly with serious consequences. The age and physical and emotional condition of the person involved can also effect the severity of an electrical shock.

Figure 1-1 Ohms Law

Resistance The resistance of the body and the degree to which the skin is insulated from the ground govern the amount of current flowing through the body. The skin offers the principle resistance which the human body presents to the flow of current. The length of time the body is in the circuit is also important with respect to severity of burns. Burns break down the skin, thereby lowering the resistance. The more extensive the burn, the less resistance provided.

Time becomes critical when current, flowing through the body, causes loss of muscular control, contraction of the chest (which affects breathing), and ventricular fibrillation of the heart. When

ventricular fibrillation occurs, the hearts pumping rhythm becomes irregular and it ceases to function properly.



Emergency Measures First Aid Everyone engaged in any electrical or electronic work should be capable of carrying out the following measures:

1 Shut off the power. Know how to cut off the power anywhere in your work area, and how to summon help in case of an emergency. 2 Free the person involved from the live circuit. If a person is "frozen" to a live electrical contact; shut off the current. Otherwise use wood boards,

poles or sticks, a belt, piece of dry rope, an article of clothing, or any nonconducting material to pull the body away from the contact and check for breathing.

3 Administer cardiopulmonary resuscitation (CPR).

4 Immediately report any shock received, no matter how slight, to your supervisor, foreman, or other appropriate authority. Promptly report any "popping" or sparking as well as any noticeable defects or hazardous conditions that could cause injury, property damage, or interference with service.



Applying power to the airplane

The aircraft electrical power system reduces crew workload and improves system reliability and maintainability. The monetary cost of these systems and the potential cost in human lives if a mishap occurred makes it absolutely necessary that good judgement, common sense and Safe maintenance practices be adhered to at all times. Virtually all Boeing Aircraft Maintenance Manuals (AMM), maintenance documents and tasks contain safety references that pertain to safe electrical practices. Technicians should become familiar with these technical documents outlining appropriate safety practices. Removing External Power After the supply of electrical power has been completed, general and specific safety procedures should be adhered to, prior to removal of external power.

Applying External Power Special attention must be paid when applying power to the aircraft. Adhere to specific warnings when supplying external power to the ground service buses, for example

Checking External Power Ensure the external power supply operates correctly before you supply external power to the aircraft. Adhere to posted safety warnings while Ensuring correct operation of external power supply units, such as



Circuit Breaker Collars When a circuit breaker is to be opened or "locked out" these special collars can be ordered to prevent accidental closing of the breaker. If these are not available, plastic tie wraps tightened around the circuit breaker head can be used instead.

Isolating the circuit When a system fault occurs and all possible troubleshooting procedures have been exhausted, it may be necessary to isolate the individual circuit and troubleshoot the system wiring. When isolating the circuit, it is absolutely necessary that the proper safety steps be followed. Alphanumeric decals identify each circuit breaker. Numbers increase from left to right horizontally along the bottom of each panel. Letters increase vertically from bottom to top along each side of the panel. The letters I, 0, and Q are not used. Circuit breaker titles are above each circuit breaker and grouped by system. Each system is identified above the circuit breaker title and the amperage value is on each circuit breaker. NOTE: Each section of the P-11 panel is hinged to permit easy access to the back of the panel.



The following procedures should be followed when attempting to isolate the circuit: 1. Identify the System Circuit Breakers. a. Refer to the Aircraft Maintenance Manual (AMM) b. Refer to the Fault Isolation Manual (FIM). c. Refer to the Schematics Diagram. d. Refer to the Wiring Diagram. NOTE: Circuit breakers are identified by a code that shows their physical location as well as their functional name. (Breaker names are not always used in

every technical source). 2. Open the System Circuit Breakers. a. Check AMM Warnings before opening circuit breakers - other systems may be affected. b. Find the Panel, Row, and Column location. c. Pull the circuit breakers. 3. Lock out the System Circuit Breakers. a. lnstall locking collars; or b. lnstall commercial locking devices; or c. lnstall tie wraps on the breakers. 4. Placard the System Circuit Breakers. a. lnstall appropriate tags with data; or b. lnstall masking tape or paper sign; or c. lnstall prepared placard. 5. Test circuit for AC or DC voltages. a. Remove the Line Replaceable Unit (LRU) from its mount. b. Check schematic diagram for power pins in the mount or connector. c. Use voltmeter to ensure no AC or DC voltages are present.



Identifying a Circuit Breaker The code for circuit breaker 11 M 6 IDLE CONT is explained this way: 11 - Location of Circuit Breaker - Panel 11 M - Row Number (horizontally). Identified by letters starting at bottom of panel. 6 - Column Number (Vertically) IDLE CONT - Name of circuit breaker



Ignition Sources WARNING: UNDER NO CONDITIONS SHOULD ANY POTENTIAL IGNITION SOURCE BE USED IN THE VICINITY OF OPEN FUEL TANKS, FUEL

VENTS OR SPILLED FUEL WHERE VAPOR CONCENTRATIONS ARE UNPREDICTABLE OR CANNOT BE CONTROLLED.

A. Fire Safety If ignition-producing equipment is used anywhere on or near an airplane where smoking is not allowed, a member of the local fire fighting crew or a person responsible for airplane fire safety should stand by to observe the work and other nearby activities. These safety practices are recommended: - Work should never begin or continue on any fuel system

component while ignition-producing equipment is present - The number of maintenance and safety personnel involved

should be kept to a minimum - The amount of emergency or fire fighting equipment that should

be at the work site must be determined by local fire fighting personnel, or other authorities, who are responsible for fire safety and are capable of judging the degree of risk associated with the work to be done.

Heat Guns, Soldering Guns, and Soldering Irons This paragraph defines the minimum recommended safety practices to use when operating heat guns, soldering guns, or soldering irons on or near in-service airplanes.

It should be noted that these recommendations are written for use throughout the world and are general in nature. Regulations established by local agencies and/or airline generated procedures may take precedence.

NOTE: Boeing can neither conceive nor document all potential sets

of conditions which the airlines may encounter. Airlines are responsible for the safe use of any of these heating devices. Explosion Potential Heat guns, soldering guns and soldering irons are not considered to be explosion-proof. The devices may contain: - Elements that may operate at temperatures in excess of the fuel

vapor flashpoint (450 degrees F) - Electrical switches that can produce sparks capable of igniting fuel

vapors.



Use in Fuel Tanks A heat device must not be operated in a fuel tank that has not been purged of fuel and filled with an inert gas, such as nitrogen. Use Near Fuel and Flammable Liquids Heat guns, soldering guns, or soldering irons should not be used within 100 feet of: - An airplane during refueling - An airplane during defueling - An airplane when fuel tanks are open - Fuel vents - Fuel spills - Other flammable liquids.



Airplane warnings These are some levels of message in the aircraft manual and the maintenance crews must be more attention during maintenance of aircraft or equipment. These messages are: WARNING: Calls attention to use of material, processes, methods, procedures or limits which must be followed precisely to avoid injury or death to persons. CAUTION: Calls attention to methods and procedures which be followed to avoid damage to equipment. NOTE: Calls attention to methods which make the job easier or provide supplementary or explanatory information.

EICAS Levels

These are the five levels of EICAS messages that inform the flight and

maintenance crews of conditions of the aircraft:

Level A WARNING Displayed in red. It tells the flight crew of conditions that require immediate action.

Level B CAUTION

Displayed in yellow. It tells the flight crew of conditions that require immediate

awareness and possible action.

Level C ADVISORY

Displayed in yellow and indented. It tells the flight crew of a condition that requires awareness.

Level S STATUS

Displayed in status page. It gives information to the flight and maintenance crews about the dispatch status of the aircraft. The maintenance crew can use the status messages together with the operator's Minimum Equipment List (MEL) or Dispatch Deviation Guide (DDG).

Level M MAINTENANCE

Displayed in maintenance page. It gives information to the maintenance crew for conditions caused by a system failure or partial failure. It can be the same as the status message. Typically, maintenance messages are inhibited in flight and will only show when an aircraft is on the ground and the page is selected.



Human factors Maintenance errors are categorized as unintentional actions, or lack of actions, within a maintenance system that lead to problems on the aircraft. Managing the Risk Air safety statistics have tended to understate the significance of maintenance as a contributing factor in accidents. Figures for the worldwide commercial jet transport industry for example, show maintenance as the "primary cause factor" in only 5.9% of hull loss accidents, compared with flight crew actions implicated as a "primary cause factor" in greater than 70% of accidents. Yet when safety issues are presented alongside the fatalities which have resulted from them on worldwide airline operations for the period of 1982-1 991, maintenance and inspection emerges as the number two safety issue after controlled flight into terrain'. Maintenance Costs Maintenance incidents are not merely costly in terms of life and property, but can also impose significant costs when flights are delayed or cancelled. In 1989, maintenance constituted 11.8% of US airline operating costs or more than $8 billion per year. Estimates show that each delayed aircraft costs the airline an average of $10,000 per hour, while each f light cancellation can be expected to cost

approximately $50,000. When these costs are considered, it is apparent that airlines stand to gain significant benefits by even a small reduction in the frequency of maintenance induced delays. Maintenance Incidents Maintenance incidents contribute to a significant proportion of worldwide commercial jet accidents. Yet, little was known of the nature of maintenance incidents and the factors which promote them until recently. In face-to-face interviews, maintenance technicians were asked to report examples of maintenance incidents they had experienced first-hand. Human factors were involved in most of the reported incidents. It was found that workers on duty between the hours of 0200 and 0400 had a greater chance of having an incident than workers on duty at other times. Difficulties with procedures emerged as the most significant factor for incidents which had the potential to affect the airworthiness of an aircraft. These difficulties included both misunderstandings and ignorance of procedures. Difficulties with tools and equipment emerged as the most frequent factor for incidents which had the potential to affect the health and safety of workers.

Human Error Most accidents to complex aircraft systems, such as electrical wiring, feature some involvement of human error. The terms "error" and "human error" are widely used in the safety field and do not imply that technicians are blamed for workplace incidents. Nevertheless, concluding that human error was involved in an accident or incident does not generally help to prevent such occurrences from happening in the future. Electrical wiring discrepancies, including cross-connections, constitute a large amount of maintenance incidents with respect to human error. Every effort must be made to decrease the potential of human factors in the workplace. ATA Specification 113 contains recommended guidelines for developing and establishing a Human Factors Program to enhance safety and aid maintenance personnel in the aircraft industry



2. Electrostatic discharge sensitive (ESDS) device handling and protection Electrostatic Discharge (ESD) Electrostatic charges: Are generated when surfaces of different materials come into contact Are stored on the surfaces of physical objects; the human body is included. Its effect on electronic/electrical devices, and ways of protecting wire harness components from static damage.

ESD from nylon or human hair onto polyethylene or steel can cause these types of damage to unprotected electrostatic discharge sensitive devices:

o Changes in basic characteristics o Degradation of performance o Catastrophic failures.



ESDS Awareness The phenomenon of ESD damage requires widespread publicity. The word must reach all areas where susceptible units are handled. All personnel must be made aware of the expensive consequences of failing to observe the correct procedures when handling equipment that has been identified as being electrostatic sensitive. In order to prevent ESDS problems, technicians must understand the growing problem of electrostatic electricity. To do this, they need to be Familiar with its evolution. Static electricity has been an industrial problem for centuries. As early as the 1400% European and Caribbean forts were using static control procedures and devices to prevent electrostatic discharge ignition of black powder stores. By the 18603s, paper mills throughout the U.S. employed basic grounding, flame ionization techniques, and stream drums to dissipate static electricity from the paper web as it travelled through the drying process. At the turn of the 20th century, lab technicians had little reason to concern themselves with the effect of static electricity on electronic components. Today, however, it is the most obvious problem with electrostatic discharge.

The vacuum tube, developed in the early 1900s to control and amplify electrical signals was prone to Severe heat and frequent failure. Yet, it was basically immune to electrostatic damage The transistor, invented in the 1940s to replace the vacuum tube, had shrunk to the size of a small pea by the 1950s. It was cooler and more reliable than its predecessor and it reduced the required maintenance of electronic equipment As they developed, transistors became increasingly smaller and were found to be susceptible to damage by static discharge. The advent of the microprocessor, or "chip", radically changed the physical characteristics of many of today's electronic parts and forced us to take a serious look at ESDS precautions. Today's technology has shrunk the size of transistors so that millions can be placed on a chip the size of a thumbnail. With each improvement of speed and size we're seeing more and more components which can be damaged by static charges well below those generated by everyday movements about a work station



Causes of Electrostatic Discharge In order to understand static electricity, we first look at how it's generated. Electrostatic discharge, or triboelectric charging, is a result of a stationary (static) charge collected by a material which is dissipated when brought into contact with, or in proximity of, a material with a different charge. It involves the transfer of electrons between materials. The atoms of a material with no static charge have an equal number of positive (+) protons in their nucleus and negative (-) electrons orbiting their nucleus. When two materials are placed in contact and then separated, negatively charged electrons are transferred from the surface of one material to the surface of the other material. Which material loses electrons and which gains electrons will depend on the nature of the two materials. Static charge is measured in volts and the amount of voltage generated is influenced by the types of materials which are interacting. In this figure demonstrates the relationship between static generating materials with respect to cotton, a neutral material. The further apart the materials are in the table, the greater the static charge generated by their interaction. For example acrylic interacting with hair generates a greater charge than polyester interacting with hair. Lightning may not seem much like static electricity, but it's actually very similar. Both are sparks of electricity created through the attraction of unlike charges.

The difference is that static electricity creates a small spark, while lightning is a huge bolt of electricity. Other everyday situations clearly illustrate the ESD phenomenon. For instance, the friction of plastic soled shoes across a nylon carpet can generate as much as 35,000 volts of static electricity. Tossing a windbreaker on a standard workbench causes up to 5,000 volts, and sliding across a foam covered chair - 18,000 volts. Even normal movements at a workbench can create 6,000 volts of static electricity.

Putting these voltages into perspective, the average persons perception level of static discharge is measured at approximately 12,000 volts, roughly the voltage when reaching for a doorknob and hearing a snap or seeing a spark. Static perception level, whether by sight sound or touch, is not an indication of whether or not damage has occurred. Many of today's electrostatic discharge sensitive devices can be functionally destroyed by less than 100 volts - well below the human perception level. One reason for this sensitivity is the size of today's components. Very thin layers of oxide are easily penetrated by static discharge. To provide size comparison, a semiconductors width, about 5/1000 of an inch, is slightly wider than a human hair. The thinness of the oxide layer is measured in millionths of an inch. Relative humidity has a profound effect on electrostatic discharges as the higher the humidity the fewer problems that occur with ESD. Studies have shown that in an area with more than 50% humidity it is more difficult for a discharge from a human to exceed 2000 volts but at 5% humidity a discharge can easily exceed 15,000 volts. Therefore, humidity doesn't prevent ESD it just reduces the voltage level in a discharge and allows for materials to more easily discharge themselves through the atmosphere than through another object.



ESDS Failures

There are two levels of damage in which an electrostatic strike can affect a circuit: Completely destroyed – referred to as

catastrophic or hard failure; or Wounded - referred to as a latent

defect or soft failure.

Hard failures are those in which discharge melts a hole in the oxide layer, fusing the metal and silicone substrate layers together. This type of damage is easily detected because physical damage is often visibly

The majority of ESDS problems are caused by static damage that is much more difficult to detect. A soft failure results from a static strike which stresses a component but does not destroy.

This may occur at as little as one quarter of the voltage required to cause a hard failure. A soft failure is categorized by either an early failure or an altered response pattern. Early failures are those which occur when the wounded part is installed and expected to be operational. Altered response patterns cause components to work intermittently. These are extremely difficult to isolate and often cause a line replacement unit (LRU) to cycle from line to shop several times before the faulty part is found. Typical LRUs contain many ESDS parts that are susceptible to soft failures. These failures translate into considerable increase in trouble shooting and handling expense. Soft failures represent approximately 90% of problems associated with ESDS parts and result in tremendous expenditures in time and resources



ESDS Protections There are four vital protective measures used: ESDS caution labels Wrist straps Approved ESDS bags Protective dust covers or "caps"

ESDS caution labels identify components that can be damaged by an electrostatic discharge. They contain an ESDS symbol and must be placed on all packaging containing sensitive components. The standard symbol for identifying potential electrostatic sensitive parts, assemblies, and packages is shown in Figure Although there are several variations and colours of the ESDS symbol, it always consists of a triangle, a reaching hand, and a slash through the reaching hand. The triangle means "Caution" and the slash means "Do Not Touch". Because of its broad usage, the hand in the triangle has become associated with ESD and the symbol literally means:

Figure of Wrist Strap

Figure of ESDS Bag

Figure of Protective Cap

Adequate protection must exist during manufacturing, assembly, storage, packaging, shipping, and handling. These can be on the line, during testing, or throughout maintenance. Basic ESDS precautions apply to all of these locations and situations. Wrist straps prevent damage to the parts by bleeding all static charges to ground. They typically contain a 250.000 Ohms to 1.5 Meg Ohm resistors to protect the user in the event they come into contact with a live wire. Wrist straps must come into contact with the person's skin to be effective, as shown in Figure 1.5. The other end must be attached to a grounded object. The best protection from ESD is to eliminate, or at least limit, its possibilities. If no electrons are lost or gained in an interaction between bodies, then there can be no electron rush between them.



General Handling Procedures

The intent of ESDS handling procedures and policies is to protect a sensitive part or assembly whenever it leaves the protective packaging by electrically neutralizing everything that contacts or is near ESDS parts. Prior to handling any ESDS labelled part, technicians must attach an approved wrist strap to themselves and to ground. If applicable, table mats should be grounded as well. When components are separated from their protective shipping container or package they should be wrapped in conductive foam, repackaged in approved ESDS bags, and sealed with a caution label. Wrapping the components in conductive foam will short the leads of these parts and prevent them from puncturing the protective bag. Once the component is sealed in the approved bag, it is safe from static discharge by ungrounded personnel or objects. Good static awareness procedures are just as important on the line,

in the overhaul shop, and in an assembly or manufacturing area. In these settings, long sleeves are a potential source of static and must be rolled up past the elbow so that they do not come into contact with ESDS parts. Shop coats and sleeve gauntlets must be made of an antistatic material, such as 100% cotton. The bench setup is another area where special precautions apply. Workbenches must be properly grounded in preparation for handling, testing, and repairing ESDS parts and assemblies. Technicians, work surfaces, and test equipment must all be grounded. Conductive and anti-static tools and equipment should be examined frequently to ensure they do not show signs of wear and tear that would negate their protective characteristics. All ESDS assemblies and parts should be returned to approve protective packaging before nonworking shifts. This ensures that they are not touched by ungrounded personnel.

Controlling ESD

1 . Treat every electronic component, circuit card, or system as if it were STATIC SENSITIVE.

2. ALWAYS use static control procedures when handling electronic

components, circuit cards, or systems. 3. Before handling a bare component or circuit card make sure all

charge is bled from your body.

This means wear a grounded wrist strap or ESD shoes or heel grounders used on static dissipative floor covering or finish.

4. ALWAYS make sure components, circuit cards, and systems are

transported and stored in static safe packaging. 5. The problem of static generation is here to stay. We can reduce

the number of sources and opportunities for damage, but the potential for an ESD strike will always exist.



Protection of ESDS Metal Encased Units

Protective Equipment Plastic dust covers/caps. NOTE: CONDUCTIVE covers/caps are black in colour. ANTI-STATIC covers or caps come in a

variety of colours and are used as an alternative when conductive covers are not available.

Both of these are made of non-conductive material treated with anti-static solution and are marked with the date the cover was treated

Front of Encased Unit

Removal Step 1: Remove the system electrical power. Step 2: Loosen and remove the unit from the

equipment rack, airframe, or panel. Step 3: Do not touch the pins in the electrical

connector. Check the unit to see if a static sensitive decal is present near the connectors. It will be labelled similar to the

Following:

The presence of such of such a label means the unit can be damaged by an electrostatic discharge through the connector pins. Install "conductive dust cover" on connectors that are labelled "static sensitive" and standard dust covers on connectors that are not labelled. NOTE:

Conductive dust covers and connector covers from the unit being installed may be used on the unit being removed.

Step 4: Transport the unit with the conductive

dust covers installed.

Installation

Step 1: Remove the system electrical power. Step 2: Do not touch the pins in the electrical

connector. Remove all conductive dust caps and

connector covers from the unit. Step 3: Install and secure the unit per the

removal and installation procedure.

Figure of LRU Rack



LRU Replacement Techniques

In this section will learn about "No Fault Found" data, LRU retention devices and re-racking procedures and CAT II & Ill landing considerations.

Boeing "No Fault Found" Data and Policies (CRR)

LRU Retention Devices Re-racking Procedures

CAT II &CAT Ill Considerations



Boeing "No Fault Found" Data and Policies (CRR) Most operators have reliability programs to identify which airplanes experience the highest number of delays or which groups of components most frequently experience unscheduled removal. However, many operators do not have a plan to optimally use the data gathered through these programs. As an alternative to reliability programs, the Component Removal Reduction (CRR) process has recently been developed to enable operators to use information about component failure to implement timely, effective corrective actions. Following the process can produce considerable cost savings for the operator. Based on an operator's complaint about excessive Short Life Units (SLU) on a fleet of four 737 airplanes, Boeing investigated the possible causes for this problem. As a result, Boeing established a process that has proved to be beneficial and cost effective in reducing the quantity of unscheduled removals of line replaceable units (LRU). By following this process, the 737 operator was able to reduce the number of replacements for line replaceable units from 32 to 18 per month. Based on an assumption that each shop visit would cost the operator $1,000 which is the monthly cost savings would be $14,000. The Component Removal Reduction (CRR) process was later introduced to another operator with similar results. The CRR Process The CRR process consists of five steps that can be tailored for individual operators:

1. Obtain and Categorize LRU List 2. Analyze Removal Reasons and Patterns 3. Determine Corrective Action 4. Implement Corrective Action 5. Follow Up After Corrective Action

1. Obtain and Categorize LRU List The first step of the process requires operators to obtain a list of all LRUs replaced in the previous month with less than 2,000 hours since the last overhaul or repair (time since overhaul [TSO]). If possible, this list should be sorted according to TSO to ensure that the primary focus is on units with the shortest service life; this is where the greatest potential cost savings can be found. The listing should include the part number (PIN), serial number (SIN), name or description, TSO, and airplane tail number (ATN).



If the list is not sorted by TSO, it should be colour coded to classify these times. For example, all LRUs that failed in 200 hours or less could be marked in red, those that failed in 201 to 1,000 hours in orange, and those that failed in 1,001 to 2,000 hours in yellow.



2. Analyze Removal Reasons and Patterns The list from step one should then be reviewed for common characteristics. These can include multiple failures of a particular PIN or repeated reports of failures to the same ATN or SIN. Shop repair reports should also be reviewed to find the causes of component failure. For example, do the reports often say "No Fault Found" (NFF) or show the same repair being done (the same component replaced) to all LRUs of a particular PIN? This can indicate some controllable action, such as incorrect handling of electrostatic discharge-sensitive (ESDS) LRUs, that is causing the failure. It can also indicate an uncontrolled environment (e.g., heat, cold, or humidity) on the airplane or in a storeroom. If more than one shop is performing repairs, the shop reports should be reviewed to determine whether the LRUs are all from the same shop. (One operator concluded that a cheaper shop was actually more expensive because the service- hour per dollar cost was higher.) 3. Determine Corrective Action After identifying the causes of early failures, the next step is to determine the appropriate corrective action. This can include asking such questions as the following:

Is an airplane or component modification available to eliminate that failure mode?

If the shop reports show excessive NFFs, are the troubleshooting instructions inadequate, are they too time consuming, or do they require special equipment that is not available on the line?

Do the troubleshooting instructions produce inconclusive results or contain faulty logic?

Is the shop using correct processes and equipment? On one job, the shop was testing the LRU without grounding the LRU case, but in the airplane

the case was grounded. The unit was repeatedly returned as NFF.

Do the shop reports or other evidence indicate ESDS abuse? This type of abuse often shows up as LRU failure around 200 to 300 hours TSO. If so, are increased training, other equipment, or improved processes required to stop ESDS abuse to LRUs? This could apply to the repair shop, line maintenance, or shipping (including customs), storage, and handling.



4. Implement Corrective Action After corrective action is identified, the next decision is whether to apply it. This decision must be made based on the operator's particular situation. For example, one operator discovered a situation involving LRUs that were supplied on a flat-rate basis. As a result, the operator saw no need to be concerned. However, after considering that their airplanes often flew into isolated airports where an LRU failure could have serious financial consequences, the operator decided to investigate the situation and resolved the SLU issue. Resolution of vendor and contract shop problems may require a visit from the operator's quality assurance manager, but these problems can usually be resolved by consulting with the shop sales representative. By using the CRR process, the operator can collect the necessary data to make the best decisions about additional training and equipment. In some cases, additional training or equipment can reduce the LRU problem, but the operator still may not be able to justify those expenses. Shipping and handling is suspect from the time an LRU is removed from its position in the airplane until it is reinstalled in another airplane. Although ESDS damage is high on the list of concealed damage, other damage, such as bearing damage, can also occur when instruments are transported without adequate padding.

5. Follow Up After Corrective Action After corrective action is implemented, SLU problems can still exist, but repeating the CRR process will show whether the cause is the same, a new cause, or a cause created by the corrective action for the original cause. Repeating the cycle will isolate the problem. After several months of applying the CRR process, operators should re-evaluate whether using it is continuing to provide cost savings. Results of CRR The following items are examples of the benefits operators have achieved by using the component removal reduction (CRR) process. Line Replaceable Unit (LRU) Removals Reduced by Nearly 50 Percent

Within six months of implementing the CRR process, one operator reduced LRU removals from 32 per month to 18 per month.



An inertial reference unit (IRU) was removed afler less than 1,000 hours in service. A check of the records for this unit showed that it had been installed five times in four years and had never lasted more than two weeks in service after each installation. The vendor exchanged the rogue unit for a new one. Another operator using the CRR process encountered a similar situation with an IRU from another vendor.

Life-Improvement Modification Applied

Investigation of multiple failures of one part number LRU revealed that a free life-improvement modification had not been performed. After the modification was implemented, the LRU no longer showed up on the short-life unit list.

Maintenance Practices Revised

A repair shop reported that an electromechanical indicator failed because of dry grease on the gear train. Inspection of an airplane, which was parked at the maintenance ramp, revealed that technicians had checked the lights in the cockpit and had left the light controls on full bright. As a result, the instrument panel was too hot to touch, and the extremely high temperature caused the grease in the instruments to dry out. The technicians were instructed to turn off the lights after checking them, and the problem did not reoccur.

Shop Practices Revised

Several computers were found to have a short life (200 to 300 hours) after shop repair. Investigation revealed that the vendor shop was not using correct electrostatic discharge-sensitive protection on repaired units. After being alerted to this issue, the vendor revised its shop practices and the life of the computers returned to normal.

Quarantine Procedures Some airlines have found a procedure that mitigates excessive "No Fault Found" failures of their LRUs. By quarantining the defective LRU in a secure area and fitting a new LRU to the airplane they can prove that the new LRU has repaired the fault. Given that the fault has been repaired with the new LRU; then the-old LRU can be sent to the repair shop for maintenance. If the fault is still within the system, and the new LRU did not repair the fault, then the old LRU should be refitted. The new LRU would then be put back to Stores as shelf stock. This procedure has been found to significantly reduce "No Fault Found" reports on LRUs. This quarantine procedure will reduce the amount of money spent on replacing an LRU that may not need to be replaced.



Different Retention Devices LRU's are held in place on the rack by retention devices. There are four different types of retention devices (see Figure 2.10): Lever Latch Type Retention Screw Type Retention Extractor Hold-Down Tridair Extractors



Lever Latch Removal Procedures Remove the electrical power by pulling the applicable

circuit breakers. Depress the lever latch allowing the lever to move

away from the handle. Move the lever in an opening direction, forcing the unit

away from the shelf mounted connector. Remove the unit from the shelf. Fit protective caps.

Lever Latch Installation Procedures Remove any protective caps from the unit. Slide the unit into the shelf with the lever in the open

position until the lever engages the shelf mounted fork.

Move the lever latch to its locked position and verify correct engagement.

Note: It is possible to determine full connector

engagement by feel. A sudden increase in handle pressure, resistance to handle movement indicates the connectors are fully engaged.



Screw Type Retention Removal Procedures

Remove the electrical power by pulling the applicable circuit breakers.

Loosen the extractor slider. Position the carriage with slots engaged in the front plate of the LRU. The extractor’s carriage should be positioned so that it will exert an outward force on the projecting lip of the units front panel.

Turn the torque knob allowing the extractor to eject the unit.

Remove the unit from the shelf. Screw Type Retention Installation Procedures

Slide the unit into the shelf until resistance from the mating connectors is noticed.

Position the extractors carriage so that it will exert an inward force on the projecting lip of the units front panel and

Tighten extractors slider. Insert the unit into the shelf by turning the torque limiting

knob until additional knob rotation has no effect on the unit.

Place the retainer cups over the hold-down hooks, tighten and safety lock the retainer nuts.



Extractor Hold-Down Removal procedures

Turn knob counter clockwise until red indicator is completely visible. Continued turning of knob provides extracting force to equipment to be removed.

Turn cup lever counter clockwise against stop. Drop extractor assembly from hold-down hook

Extractor Hold-Down installation Procedures

Turn knob counter clockwise against stop. Turn cup lever counter clockwise against stop. Lift extractor hold-down to engage hook. Turn cup lever clockwise against stop. Verify

that hold-down hook is engaged. Turn knob clockwise until red indicator

disappears into end of knob. This indicates equipment is properly held in rack.

Test the unit per the applicable system test.



Tridair Extractor Removal Procedures

Open the applicable circuit breakers to remove electrical power. Turn the front hold-down extractor knob counter clockwise to disengage the extractor clutch. Turn the keeper to align the deep slot with the T-hook.

Lower the extractor off the T-hook.

Note: Some LRU's are static sensitive. Take the necessary precautions when you are to remove the boxes. Read the procedure on how to hold electrostatic-discharge sensitive devices (AMM 20-41-011201). The LRU's contain devices that can be damaged by static discharge.

Carefully remove the box out from the tray.

Note: The LRU front face can be moved right to left (about 118 inch). This will help disconnect the box from the electrical connection. .

Make sure that the connector is fully disengaged before removal. Install dust caps on the electrical connector and on the tray electrical connector. Remove and discard any O-rings from the rack-mounted electrical connectors, if installed.



Tridair Extractor Installation Procedures

Make sure that the rubber plugs are installed in the metering tray at the correct locations. Compare the tray orifice configuration with that shown on the decal.

Remove the dust caps. Make sure that the tray gasket and restrictor plugs (adjustment number) did not move. Install if necessary. Make sure that the guide pins on the tray will engage with the LRU connector.

Note: Electrical pins on the LRU connector and the tray connector must not be bent or damaged. Installation with damaged pins could result in damage to the LRU connector, the tray electrical connector, or the system components.

Carefully move the EIE box in the tray and engage the electrical connector

Note: The LRU front-face can be lifted about 118 inch above the tray surface or moved right to left (about 118 inch). This will help engage the electrical connector. During installation apply a light pressure to the front-face of the box. Do not use force during installation.

Turn the keeper to align with the shallow slot with the T-hook. Set the extractor on the T-hook and turn the keeper 180 degrees. Tighten the front hold-down extractor. Turn the front hold-down extractor clockwise until the extractor clutch is fully engaged. Move the LRU left to right. Make sure that the EIE box is tight. Tighten the extractor. Make sure that the electrical connector is engaged. Install the connections to the LRU front if applicable. Close all applicable circuit breakers.



LRU Re-Racking Procedures Before the technician replaces any slide-in LRU, it may be advisable to remove the LRU from the rack and visually inspect it for external damage. Always be sure to check the LRU connectors for signs of corrosion, bent pins, or any other damage that could possibly degrade the performance of the LRU. After ensuring that there are no signs of physical damage to the LRU exterior, reinstall the LRU into the rack and perform another LRU test. If the LRU is functioning properly, there may not be a need to replace it. If the problem continues, follow the prescribed maintenance procedures for that particular component. This step, re-racking the LRU, may save time and money that would have been otherwise wasted on replacing a part that would not necessarily need to be replaced. Certification Considerations (CAT I1 I CAT Ill Landings) This section will help you understand some basic concepts of CAT I1 and CAT Ill landings and some considerations for certifying the aircraft after maintenance has been accomplished. Airlines and operators must have their own approved CAT II and CAT Ill operations and maintenance programs based on their specific regulatory agency requirements. The authorization for CAT II and CAT Ill landing procedures are found in the Operations Specifications (OpSpecs) Category 111111 manual, or the equivalent document issued by the operator's national regulatory agency. The OpSpecs describe in detail the pilot qualifications, airborne and ground equipment, and weather conditions required for each approach procedure.

Approach Categories:

Category DH RVR

CAT II

100 feet

1200 feet

CAT lllA

*

700 feet

CAT lllB

*

**

CAT lllC

#

0 feet

(DH Decision Height, RVR - Runway Visual Range) 50 feet with fail passive landing system. None with fail-operational

landing system

** 600 feet with RVR. 400 feet RVR with rollout guidance # 0 feet with 0 feet RVR. NOT CURRENTLYAUTHORIZED



What is the difference between a CAT II and a CAT Ill landing? CAT I1 landings provide sufficient visual reference at the DH to permit a visual landing. CAT Ill does not necessarily provide a sufficient visual reference and thus requires an automatic landing system and/or a manual flight guidance system. There are three levels of CAT Ill airplane certification: CAT IllA, CAT IllB, and CAT IllC. An airplane's specific CAT Ill landing system is considered either "Fail Passive" or "Fail Operational".

CAT lllA -A precision instrument approach and landing with a DH lower than 100 feet or no DH, and an RVR not less than 700 feet.

CAT lllB -A precision instrument approach and landing with a DH lower than 50 feet or no DH, and an RVR less than 700 feet but not less than 150 feet. CAT IlIC -A precision instrument approach and landing with no DH and no RVR limitations. CAT IIlC operations are not currently authorized.

CAT II/III Airplane Maintenance Program It is the responsibility of the operator's maintenance department to establish a program to ensure reliability of the airborne equipment for CAT II/III operations. Normally, the Digital Flight Control System (DFCS) Land Verify test is used to return the airplane to CAT II/III status, after repair or replacement of "system critical" components listed in the operator's MEL. The particular procedures for maintaining the airplane to CAT II/III status will be identified in the Operator's Maintenance Manual. Specific CAT II/III training is required for maintenance personnel on at least an annual basis for applicable procedures, as specified in the Operator's General Maintenance Manual. Training will consist of both initial and refresher training for maintenance personnel who will be upgrading and downgrading airplane status as per the operator's MEL. This includes a review of the basic CAT II/III operations, a review of airplane systems required for CAT II/III operations, and a review of specific Airline/ operator procedures for upgrading or downgrading the airplane. A record of training for each person with Airworthiness Release Authority, is maintained by the airline training department, noting the dates for training and the scores on written tests during the training.

Part C Electrical Wiring Interconnection Systems


Important Information

In this section you will learn about the overall objectives of this manual, general information about inspection practices in regards to airplane wiring, the ATA MSG3, and levels of inspections.

Module Objectives

About Airplane Wiring Inspections

ATA MSG3

Levels of Inspections



Module Objectives This module introduces and explains: o The terms and standards associated with airplane wiring inspections; o Zonal inspection criteria; o Ideal conditions of wiring components in each major airplane zone; o Typical wiring system damage; and o Human factors in inspection.



About Airplane Wiring lnspection

Over the years, technicians, inspectors, and other maintenance personnel have not viewed airplane wiring components as a system, but rather as auxiliary components of other systems. This has led to an unintentional neglect of wire system components. Wiring as a system has been virtually absent of inspection criteria and standards, and those that do exist have been loosely defined and minimally consistent. This Module explains the terms and practices associated with airplane wiring inspections. The practices will focus on the wiring system as a whole, rather than specific requirements for each of the vast amount of components. They will also focus on commercial aircraft in general rather than specific models or manufacturers. These practices are to be used by technicians as a foundation of which to build and establish airplane wiring inspection procedures for their respective companies or organizations. Some of the practices may not be universally translated to all makes and models of aircraft, but the basic framework and principles of inspection should be. Again, it is up to the technicians to take this information and apply it to their own organizational situations. Aircraft Maintenance Manuals identify zonal inspection criteria set forth by Maintenance Planning Data. Task Cards are then developed to detail specific steps to perform the inspections. However, in the past, these procedures have lacked the proper emphasis needed for inspection of wire harnesses and other wiring system components. This Module is designed to increase technicians' awareness of wiring system component locations and the potential damage that may occur. It is not intended to replace existing inspections, but rather to enhance them.



ATA MSG 3

This Module focuses on "Zonal Inspections", rather than individual components or systems. This is based on the Air Transport Association (ATA) Maintenance Steering Group -3 (MSG-3) Zonal Analysis Procedures, as well as, recommendations from the Aging Transport Systems Rulemaking Advisory Committee (ATSRAC) Task 3 Sub Committee. The ATA MSG-3 provides guidance on a logical means to identify a minimum list of applicable and effective maintenance tasks that maintain the inherent safety and reliability levels of the systems and structure of the airplane. It is used to determine initial scheduled maintenance requirements and contains an analysis process that identifies all scheduled tasks and intervals based on the aircraft's certificated operating capabilities. The original MSG-1 was developed in 1968 to design a scheduled maintenance program for the new Boeing 747. It was later revised into a universal document that was applicable for new type aircraft and it was renamed MSG- 2. In 1979, ATA decided that another revision was both timely and appropriate. The new MSG-3, issued in 1980, was built on the framework of MSG-2, but contained a number of differences in the organization and presentation of material and in the detailed procedural content. The MSG-3 was revised in 1988, 1993, 2000, and again in 2001. Today, the objective of the document is to present a means for developing the scheduled maintenance tasks and intervals which will be acceptable to the regulatory authorities.



Levels of Inspections There are three levels of inspections identified in the MSG-3: General Visual lnspection (GVI), Detailed lnspection (DET), Special Detailed lnspection (SDI)

General Visual lnspection (GVI) Is a visual examination of an interior or exterior area, installation, or assembly to detect obvious damage, failure, or irregularity. This level of inspection is made from within touching distance unless otherwise specified. A mirror may be necessary to enhance visual access to all exposed surfaces in the inspection area. This level of inspection is made under normally available lighting conditions such as daylight, hangar lighting, flashlight, or droplight and may require removal or opening of access panels or doors. Stands, ladders, or platforms may be required to gain proximity to the area being checked. Detailed lnspection (DET) Is an intensive examination of a specific item, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at an intensity deemed appropriate. Inspection aids such as mirrors and magnifying lenses may be necessary. Surface cleaning and elaborate access procedures may be required. Special Detailed lnspection (SDI) Is an intensive examination of a specific item, installation, or assembly to detect obvious damage, failure, or irregularity. The examination is likely to make extensive use of specialized inspection techniques and/or equipment. Intricate cleaning and substantial access or disassembly procedure may be required.

Zonal inspection A collective term comprising selected general visual inspections and visual checks that are applied to each zone, defined by access and area, to check system and power plant installations and structure for security and general condition



Zonal Inspections

In this section you will learn about the breakdown of individual airplane zones and details of Zonal Visual General lnspections and zonal inspection programs Breakdown of Zones Zonal GVl . Zonal Inspection Programs

.



Breakdown of Zones

Most commercial aircraft are divided into eight major zones. These zones are: 100 Fuselage-Lower Half sub zones. 200 Fuselage-Upper Half 300 Empennage 400 Power plants 500 Wing-Left 600 Wing-Right 700 Landing gear and gear doors. 800 Doors-Passenger and Cargo A further breakdown in zone identification is achieved by subdividing the individual major zones into sub zones. Zonal Inspections are performed according to these sub zones. Each airplane model has its own division of sub zones. The specific division of sub zones is identified in the Maintenance Planning Data for the Model. This Figure shows how the sub zones are divided in major zone 100 of the Boeing 757



Zonal GVI

Zonal GVI requires a visual examination to detect obvious unsatisfactory conditions and discrepancies. Unless otherwise noted, it is performed from within touching distance from the technician's eye to the item or area being inspected. Flashlights and mirrors may be required to provide an adequate view of all surfaces, but there is no requirement for equipment removal or displacement unless this is specifically called for in the access instructions. Removal of paints and/or sealants is not necessary and should be avoided unless unsatisfactory conditions are suspected. When unsatisfactory conditions are suspected, items may need to be removed or displaced in order to allow correct assessment. The area to be inspected should be clean enough to minimize the possibility of accumulated dirt or grease hiding unsatisfactory conditions that would otherwise be obvious. Any cleaning that is considered necessary should be performed in accordance with approved procedures in order to minimize the possibility of the cleaning process itself causing damage to components. The inspector is to identify wire harness degradation and make assessments regarding appropriate actions to be taken. In making this assessment, the inspector should consider the influence of any adjacent system installations, particularly if these include wiring

.



Zonal lnspection Programs Zonal inspection programs detail scheduled maintenance tasks. They are located in the Maintenance Planning Data and in Task Cards. They are not specific to wiring, but to all systems that have components in each particular area. They are arranged by airplane zones and assure that all components contained in a zone receive adequate surveillance to determine security of installation and general condition. This Figure shows a sample task card for the Boeing 757 Zonal lnspection Program. This card identifies



Wiring System Components

In this section you will learn about the ideal conditions of wiring system components located in each of the eight major airplane zones. Zonal Areas Ideal Conditions Major Zone 100 Major Zone 200 . Major Zone 300 Major Zone 400 Major Zone 500/600 Major Zone 700 Major Zone 800



Major Airplane Zones

To help simplify the identification of wiring system components, we have separated the aircraft into the eight different sections or "major zones" identified in Figure 3.1. For the purpose of conducting a zonal inspection, each major zone is divided into smaller sections or "sub-zones". However, for simplicity, we will look only at the eight major zones and identify the specific wiring system components they contain.

Because of the many different airplane manufacturers, models, and variations, this zonal breakdown cannot be used for all airplanes

We have designed this section based on the most common configurations found throughout the commercial airline industry. Technicians should use this section as a starting point for developing inspection routines for the models and variations of aircraft they maintain. This Figure for shows the primary wiring system components found in each of the, eight major zones. All of which contain wires. And wire bundles. The remainder of this Section describes and illustrates the ideal conditions that should exist in each major zone. When conducting an airplane wiring system inspection, terminals, splices, connectors and other wire harness components must be inspected



Ideal Conditions In order to properly perform inspections, technicians must know what they are looking for. It is impossible for them to identify components that are damaged if they are not familiar with the conditions that the components should be in under ideal circumstances. To simplify the inspection process, we identify the primary wiring system components grouped according to the numerical order of the major zone in which they are found. It is not imperative for technicians to perform inspections in this same order, yet it is important that their inspections include examination of all wiring system components identified



Major Zone 100 Fuselage-Lower Half The lower half of the fuselage contains the electrical centers, environmental control system, many wire bundles that run the length of the airplane, and cargo areas. The details of inspection in each area are explained for these specific areas, but there are also some general guidelines to follow throughout this zone. Because this zone lies beneath the cabin floor, it is the recipient of large amounts of cabin-generated debris and contamination. This is especially true during heavy checks when the cabin floor boards are removed and machining is performed. FOD and other debris can fall onto exposed wire harnesses and cause damage. Many areas in this zone may require cleaning prior to checking of components. Technicians must also be- careful not to cause further damage to components during inspection by limiting contact as much as possible. This decreases physical displacement and contamination cause from human-wiring interface. Cargo and baggage can cause damage to wire harnesses located behind protective wall coverings. They can puncture these protective coverings and physically displace and crush wiring components. In general, wires and wire bundles should be inspected for insulation damage such as abrasion, cracking, crushing, cuts, and discoloration. Any breaches of wire insulation that exposes the bare conductor requires immediate repair. Clamps should be inspected for correct installation and fittings. Connectors should be inspected for proper seals, backshells, torques, and corrosion.



The main electrical center is the heart of an airplane's wiring system. This is where the electricity generated by the power plants is transferred to the rest of the aircraft. Inspection of this area should focus on wire insulation integrity, bundle ties and clamps, LRUs, batteries, and power feeder connections. Wire insulation is very susceptible to damage from human-wiring interface. It is exposed to contamination, physical displacement, and abrasion from technician contact. Bundle ties and clamps should be installed correctly and replaced accordingly when LRUs are interchanged. Technicians should verify that all clamps and ties are snug around wire bundles to prevent abrasion from vibration. LRUs should be checked for wear and tear of connectors and retention devices. These are subject to damage when LRUs are installed and removed.

Batteries should be inspected for spillage of electrolytes and proper installation. Battery cables should be checked for terminal damage from connection and disconnection. Power feeder connections should be checked for correct torque, high-heat damage, and arcing damage. Heat damage is evidenced by blackening of feeder terminals.



The auxiliary electrical centers are susceptible to the same forms of contamination and damage as the main electrical center, but to a lesser degree because of they contain fewer components. They should be inspected accordingly for damage to wire insulation, bundle ties and clamps, LRUs, and micro switch assemblies. All electrical centers can be susceptible to grease contamination. Grease can drip from control cables onto wire harnesses and LRUs. Inspection of this area may require cleaning before component can be checked.

Micro switch assemblies transmit the position of the thrust levers to the airplane. Care should be taken during airplane inspection to make sure that wire bundles and terminals of micro switch packs are not distorted as these may cause rigging problems. Dirt, dust, and debris contamination must be removed to ensure correct operation of switches.



The environmental control system produces high-heat conditions that can damage surrounding wire harnesses. Inspection of this area should focus on heat damage to wire insulation, splices, connectors, and terminals. Heat damage to wire insulation and splices is evidenced by discoloration, hardening, or even melting. Wires in this area should be protected by metallic-braided coverings as shown in Figure 3.8. Connectors and terminals should be inspected for degraded seals, cracked backshells or collars, damaged pins, and proper crimping. Any corrosion or any damaged components should be repaired immediately.



Cargo areas contain many wire harnesses that run the length of the airplane. These wire harnesses are in the walls, ceilings, and floors of cargo areas and should be inspected for physical damage, displacement, and contamination. Physical damage can occur when cargo and baggage are loaded, stored, and unloaded. They can puncture the protective coverings of walls and damage components. Overhead wire bundles should be inspected for correct installation of bundle ties and clamps. They should fit snug around the bundles to prevent abrasion and physical displacement. Technicians should verify that ties and clamps are installed close enough to provide sufficient support of wire bundles. Contamination is prevalent in cargo areas because of spillage and FOD. inspection may require initial cleaning of the area prior to checking components.



Major Zone 200 Fuselage-Upper Half

The upper half of the fuselage contains the passenger cabin compartments, galleys, lavatories, many wire bundles that run the length of the airplane, and the in-flight entertainment system. The details of inspection in each area are explained for these specific areas, but there are also some general guidelines to follow throughout this zone. Most areas in this zone are pressurized and can be oxygen-rich. They are also occupied areas where large amounts of dust and debris are generated by passengers. For these reasons, the danger of fire from damaged wire components can be higher than in other areas of the airplane. Dust generated by passengers and crews is flammable. In an oxygen-rich environment, this dust can be ignited by arcing from damaged wire insulation. Inspection should include vacuum extraction of dust prior to checking components to decrease the potential fire hazard. Technicians must also be careful not to cause further damage to components during inspection by limiting contact as much as possible. This decreases physical displacement and contamination caused from human-wiring interface.

In general, wires and wire bundles should be inspected for insulation damage such as abrasion, cracking, crushing, cuts, and discoloration. Any breaches of wire insulation that exposes the bare conductor requires immediate repair. Clamps should be inspected for correct installation and fittings. Connectors should be inspected for proper seals, backshells, torques, and corrosion



The flight compartment receives large amounts of dust and debris because it is an occupied area. It also has a high density of wiring components in a possible oxygen-rich environment. These two factors are the focus of inspection. Dust is flammable in any environment. Technicians

should use vacuum extraction of dust and debris when performing inspections to decrease potential fire hazards caused from possible

breached wire insulation. Components behind the flight panels should be inspected for signs of arcing, clamping deterioration, pinched wiring, and contamination. Terminals and connectors with signs of corrosion, and wires with breached insulation should receive immediate maintenance.



There are few wiring components located in lavatories, but they are very susceptible to contamination and physical displacement. Blue-water spillage can cause contamination damage to components and accelerate wire degradation. If blue water spillage occurs, technicians should inspect the area below the lavatory for seepage into the lower fuselage with possible damage. The toilet-tank pump motor should be inspected for Overheating, especially in older aircraft. Signs of overheating include discoloration, smoke odor, and malfunction.

The galley areas contain LRUs and their power supplies. LRUs should be checked for wear and tear of connectors and retention devices. These are subject to damage when LRUs are installed and removed. Power supplies should be inspected for corrosion caused by spillage of soft drinks, coffee, and other fluids in the galley.



Overhead wire bundles should be inspected for correct installation of bundle ties and clamps. They should fit snug around the bundles to prevent abrasion and physical displacement. Technicians should verify that ties and clamps are installed close enough to provide sufficient support of wire bundles. There should not be any bundle movement through clamps or ties to prevent abrasion and deterioration from vibration. The semi-rigid foam in raceway clamps deteriorate over time and should be replaced if worn. All wires and wire bundles should be placed in clamps in a manner that does not cause the wires to bend or be pinched. These conditions can cause wire insulation to be breached.



The in-flight entertainment system components are located overhead and under the seats. Both areas are susceptible to damage and should be inspected. The seat controls and some components of the in-flight entertainment system are located under the seats. These components are subjected to far more potential damage than those that are overhead because they can easily be physically displaced by feet, luggage, and other objects placed under the seats. They must be inspected for damage to wire insulation, splices, connectors, terminal, and LRUs. Typical under-seat damages include abrasion, stretching, and cutting of wire insulation and splices, cracked connector backshells and collars, and contamination of terminals and LRUs from spillage. Overhead in-flight entertainment system components are subject to the same damages as other over head wire harnesses. They can also at risk to physical displacement because they are suspended from the ceiling where they can be displaced by maintenance or passenger loading.



Major Zone 300 Empennage

Inspection of the wire harnesses in the empennage should be separated into two parts: The first part is the APU area. Because the APU produces heat and vibration, the wire harnesses in this area should be inspected for discoloration abrasion or cracking that leads to breaches in wire insulation. Splices and connectors should be inspected for damaged or degraded seals. All components should also be inspected for abrasion and other vibration damage, especially wires and wire bundles around clamping points. They should also be checked for possible contamination from APU oils and corrosion.

The second area is the horizontal and vertical stabilizers. The wire harnesses in this area can be subjected to high levels of vibration and potential physical displacement. Technicians should inspect wires and wire bundles around clamping points for abrasion and breaches of insulation.

Clamps should fit snug around wires and bundles without pinching or bending them. This can also prevent physical displacement of wire harnesses in the leading and trailing edges caused by wind, rain, and de-icing fluid application. Technicians should also check for any Skydrol contamination and remove any that is found.



Wire harnesses on and around the APU are subject to high levels of heat vibration and oil contamination. Technicians should inspect wires and wire bundles for discolored, cracked, and/or breached insulation. Connectors and splices should be inspected for degraded seals and serviceability.

Wire harnesses in the horizontal and vertical stabilizers are susceptible to damage from the high level of vibration in the area. Wires should be inspected for abrasion around clamps and the clamps should be inspected for proper installation and fitting. Wire harnesses in the leading and trailing edges should be inspected for corrosion and physical displacement caused by wind, rain, and de-icing fluid application. Any corrosion should be removed and r any damaged components should be repaired immediately. Figure 2.23 Wiring Components in Horizontal Stabilizer

The APU power feeders should be inspected for heat damage such as discoloration, cracking, or breaches. The terminals connecting to the APU should be checked for corrosion and torque of hold-down nuts. Any corrosion should be removed and any damaged components should be repaired immediately. They should also be inspected at the pressure bulkhead seal and at clamping points for any abrasion caused by vibration. The pressure bulkhead seal should also be inspected for integrity.



Major Zone 400 Power plant Wiring in the power plant area is subjected to high levels of heat, oil, vibration, and corrosion. Inspection of the wire harness in this area should focus on these four factors. Because of the extreme heat generated by the engines, technicians should check for heat damage such as discoloured, cracked, or breached wire insulation. They should pay particular attention to components close to bleed-air ducts for any potential damage. Inspection may require initial cleaning of the area prior to checking components because of oil contamination. Technicians should check connector seals for swelling and contamination that has penetrated into connectors. They should also check for any corrosion, deterioration of rubber clamps, and damage to any heat-shrink protectors caused by engine oil contamination.

Air, rain, de-icing fluids, and oils can accelerate corrosion of connectors and terminals in this area. Technicians should inspect components for any corrosion, remove any that is found, and inspect the components for Serviceability.

Vibration in this area can cause wire insulation to become abraded and breached. Technicians should pay special attention around clamping devices for these conditions.



Engine System Wiring Electronic Engine Control

Power Feeder Clamps

The main power feeders should be inspected for heat damage such as discoloration, cracking, or breaches. The terminals connecting to the engines should be checked for corrosion and torque of hold-down nuts. Any corrosion should be removed and any damaged components should be repaired immediately.

Main Power feeder Terminal



Major Zone 500 Left Wing and Major Zone 600 Right Wing

The wire harnesses located in the wings of an airplane are at risk of vibration damage and air displacement than in any other area. It is important for technicians to focus their inspection of this area on identifying and preventing such damage. All clamping points and bundle ties should be checked for correct installation, spacing, and serviceability. Wires and wire bundles should fit snug in clamps without being pinched or loose. Wire insulation that is pinched in clamps can be easily cut and breached. Clamps that are too loose cause rubbing, which leads to abrasion and possible breaches of wire insulation. Air, wind, rain, de-icing fluid application, and other debris can cause physical displacement and corrosion of wire harnesses. Technicians should check all components and repair any damage immediately.



Fuel Quantity Indicator Wiring

Fuel Quantity Indicator Wiring

Trailing Edge Wires

Technicians should inspect the fuel system wiring for loose bonding terminals caused by improper torquing or vibration. Checking these can decrease the chance of sparks being generated that could ignite fuel vapors in the area.



Leading Edge Wire Clamps Wire harnesses in the leading and trailing edges of the wings are susceptible to damage from air displacement and vibration in the area.

Trailing Edge Wires Bundles

Wires should be inspected for abrasion around clamps and the clamps should be inspected for proper installation and fitting. Wire harnesses in the leading and trailing edges should be inspected for corrosion and physical displacement caused by win, rain, and de-icing fluid application. "Plucking' of individual wire insulation and lost tie cords must be repaired.

Leading Edge Wire



Copalum Splice

Technicians should inspect the outer sleeve and insulation around Copalum splices because they can deteriorate over time and expose the splices. Also, heat can be generated by faulty splices and degrade the sleeves from within which is evident by discoloration. If these sleeves are discoloured the sleeve must be removed and the splice inspected for high resistance. Replacement of the splice may be necessary. Power feeders should be inspected at pressure bulkhead seals and at clamping points for any abrasion caused by vibration. The pressure bulkhead seal should also be inspected for integrity. Bleed-air ducts are high-heat sources that pose potential danger to wire harnesses. Technicians should inspect components near bleed-air ducts for heat damage such as discoloured, cracked, or breached wire insulation.

Power Feeder at Bulkhead Seal

Bleed Air Duct



Major Zone 700 Landing Gear

Inspection of the wire harnesses associated with the landing gear and wheel well areas should focus on damage cause by debris and contamination. These components are subjected to high amounts of debris such as dirt, water, sand, FOD, and other environmental contaminants. Technicians may need to clean them prior to inspection in order to inspect all components sufficiently. Cleaning should only be done as needed to properly inspect components, or unnecessary physical displacement can occur. Contaminants can cause physical displacement and damage to components. They can also cause damage to these components that allow debris to effect their inner parts. Technicians should check all components for breaches of insulation, seals, and other protective barriers. Hydraulic oils are prevalent in these areas and can lead to accelerated damage. They are highly reactive and deteriorate components faster than other contaminants.

Signs of vibration damage should also be checked in these areas. Vibration causes damages noted in other zones and should be inspected for in this zone as well. Another hazard in this area is tire-burst damage. When tires burst, debris can be sent into the area at high speeds causing physical displacement and damage to components. If this happens, tire debris should be removed and all components should be inspected. Hydraulic oils can deteriorate clamps, seals, potting compounds, and wire insulation faster than other contaminants. They cause failure of connector seals, inserts, and pin-retention devices. Over time, they will deteriorate all components they contact and cause damage to the wiring and other systems.



Wire harnesses in the forward wheel are subject to large amounts of water, debris, and contamination. Cleaning may be required prior to inspection. Vibration is also a danger to components in this area. Clamping points and bundle ties should be checked and repaired if needed. Lighting circuits should be inspected for damage from overheating. Terminals, splices, indicators, and proximity switches should be checked for cracking and corrosion. Damaged components should be repaired immediately.

Forward landing Gear Indication

Forward Wheel Well Wiring



Major Zone 800 Doors The interior wire harnesses in the doors are protected from most forms of physical damage and contamination, but the exterior wiring components are not. Technicians should focus inspection on the components connecting the door motors, lights, and indicators. The wires connecting the door motor should be covered in protective conduit but allowed to flex with opening and closing of the door. Technicians should inspect these wires for correct clamping and bundle integrity. Any wires that are pinched by clamps or by the doors can be cut, abraded, and/or breached. The motor itself should be inspected for signs of overheating and physical damage. The wire harnesses connecting the door lights and door indicators should be inspected for damage and contamination. Any damaged components should be repaired and all corrosion should be removed immediately.



Cargo Door Motor Wiring

Cargo Door Proximity Switch

Cargo Door Motor



Typical Wiring System Damage

In this section you will learn about the typical wiring system component damage to look for when conducting general visual inspections.

Wires and Wire Bundles

Connectors

Switches

Ground Points

Bonding Braids and Jumpers

Clamps



Wires and Wire Bundles

Sagging Wire Bundle

Wire bundles not supported or clamped properly can sag. This causes excessive stress on existing clamping points and can cause abrasion and insulation breaches. Technicians must make sure that no more than 112 inch of free movement is allowed.

Improper Support of Wire Bundle Causing

Abrasion

Missing Bundle Ties



Using a plastic tie strap improperly can be a damaging to wires as not using one at all. Improperly applied tie straps can cause abrasion damage to wire insulation, cause the insulation to become breached, and cause mechanical damage to the wire.

Damage from Plastic Tie Strap

Lacing Tape Improperly Installed

An improper bend radius can cause protective sheathing to become branched and wire to become damaged

Improper Bend Radius

Improperly installed lacing tape can cause chafing and damage to individual wires in bundles. Technicians must check tapes for proper installation and wires for acceptable conditions.

Missing bundle ties can cause wire bundles to come apart and become chafed. Technicians must look for signs of damage to wires and replace any damaged or missing bundle ties and clamps.



Heat Damaged Wires High heat from engines, APU, hot air ducts, or other sources can cause dryness and cracking of wire insulation. Even exposure to low levels of heat over long periods of time can damage wire harness components

Dust, Metal Shavings, and Other Debris on

Wire Bundles



Connectors

Corroded Connectors

Contamination can include oils, greases, debris, dust, swarf, dirt, and many other substances that can damage connectors. Technicians should remove contamination according to the SWPM prior to inspection. This makes it easier to see all components and identify any potential damages. Cleaning should only be done when necessary in order to prevent additional damage from human contact.

Contaminated Connectors

Corrosion causes premature degradation of connector contacts. This corrosion can damage the external and internal components of connectors. External damage is easily seen as build up or deterioration. Internal damage can only be detected by disassembling connectors and checking contacts and retention devices for proper working conditions.



Connectors Missing Strain Relief

Broken backshells

Connector Missing Safety Wire



Switches Switches fail due to high heat and increased resistance on the internal contacts. Technicians should check for indications of heat or other damages to the exterior of switches that may indicate internal damages. Damage to protective sleevings or caps on the rear of switches should also be checked for damages caused by contact from humans or other devices, contamination, and corrosion.

Damaged Protective Sleeving

Ground Points

Grounding points are susceptible to corrosion because there is little or no protective coatings between the ground and structure. Technicians should pay particular attention to areas exposed to weather and the external environment because moisture from rain, snow, condensation, and other factors can accelerate corrosion. Zinc chromate primer will help prevent deterioration of ground points after the connection has been made.

Bonding Braids and Jumpers

Bonding is critical to lightning strike and HlRF protection. Technicians should make sure that all bonding straps are as short as possible and are in good condition. Good condition means that the bonding straps are not frayed, are intact and connected properly, and are without corrosion, contamination, or physical damage.



Clamps Clamps are used to secure wire harnesses to the airplane structure. The wire harnesses supported by clamps must not move within the clamp. Any movement can cause abrasion of wires and wire bundles. This can lead to breaches in wire insulation and arcing. Technicians should check for any movement of wire harnesses within clamps, but be careful not to cause unneeded damage from human contact. Any movement necessitates immediate maintenance. This includes tightening or replacement of the clamp and must be in accordance with the SWPM.

Loose Clamp

Broken Clamp

Bent Clamp

Note: Wires or bundles in clamps must not be

able to move with light hand pressure. However, with heavy hand pressure there will be movement.

Damaged Cushion on Clamp



Human Factors in Inspection In this section you will learn about the human factors that compromise airplane safety and can inhibit successful airplane wiring inspections.

Maintenance Errors Factors Physical Health Time Constraints Fatigue Peer Pressure Workplace Distractions Personal Stress Complacency The MEDA Process



Maintenance Errors Maintenance errors are categorized as unintentional actions or lack of actions within a maintenance system that lead to problems on the aircraft. There are two ways in which maintenance errors are discovered: Faulty equipment Inspection. The first, and most expensive, is a fault in equipment or systems that occurs during airplane operations. This can lead to costly maintenance, excessive flight delays and cancellations, or even major accidents. The second, and most preferred, is through inspection. By conducting inspections of systems and components, many maintenance errors can be discovered at little expense. The only expenses are related to parts and labour to correct the error found.

Maintenance Work

Most Common Maintenance Errors

Technicians must be aware of common errors and look for them during inspections. These may not be detected as easily as contamination or damage, so the technicians must be knowledgeable about the zone, system, or components they are inspecting. The eight most common maintenance errors are listed in Figure



Factor Maintenance error can be caused by many factors. Awareness of this can help to reduce their instances. The seven most common human factors related to maintenance error are : Physical health Time constrains Fatigue Peer pressures Workplace distractions. Personal stress Complacency

Exercising Regularly Will Boost Energy

Physical Health Poor physical health can be the result of an illness or poor lifestyle choices. An illness is usually temporary and can be managed easily if technicians are honest with themselves and others about their capabilities at a given moment. If an ill technician is taking medication, they should read and comply with directions on the label or package insert. Rest and time-off can often aid in recovery and be more cost-effective than poor workmanship. Poor lifestyle choices usually effect job performance for longer durations than an illness. These include diet, addiction, stress, physical activity, etc. Technicians suffering from problems that are too big for them to solve on their own should seek help in dealing with them.



Time Constraints

The pressure of avoiding flight delays and cancellations can cause technicians to perform less-than-standard work. If sufficient time is not available to complete a task, then technicians must communicate honestly with the appropriate people and maintain their professional integrity Fatigue Fatigue can be caused by a number of preventable factors such as sleep, stress, and work conditions. Technicians should be sure get a minimum of five hours of sleep per night (many need more), maintain regular sleep/wake habits, develop healthy eating habits, and exercise consistently. On the job, technicians should work in well-lit areas and avoid performing long and tedious tasks without stopping. Also, working in pairs promotes conversation which increases alertness.

Peer Pressure Negative peer pressure can be hazardous in the workplace. It can cause technicians to be indecisive, lack confidence, and perform at a less-than-optimum level in order to gain approval of others. To counteract this pressure, technicians must question any procedure that they think are not correct and maintain their professional integrity. Personal Stress Stresses in personal life can have an effect on job performance. Technicians can reduce stress by talking about it with others, eating healthy, exercising, and getting sufficient rest. If appropriate, they should seek help. Resources are available for many personal problems. Complacency Continuous repetition of the same tasks can dull the senses and lead to lackluster performance. Technicians can combat this by varying the tasks they perform. They can stay mentally alert by being thorough in their performance and checking every detail. During inspections, they should expect to find something wrong, this is because people often find what they expect to see instead of what they do see.



Workplace Distractions The workplace is often filled with people and objects that can interrupt technicians in the middle of a task. Another worker with questions, the phone ringing, a spill, an accident, and many other things can cause technicians to become distracted. Avoidance of these distractions is the best way to limit their effect on task completion, but this is not always feasible. The best way for technicians to deal with unavoidable distractions is to document where they stopped. This can be done by marking or circling the procedure step number if following a written process, writing some notes down on a piece of scratch paper, or putting a piece of tape or paper on the object indicating where they were when the interruption occurred.

Worker Talking on the Telephone

Upon returning to the task, technicians should go back three procedure steps prior to where they left off. This gives them a chance to verify that all steps were completed, as well as, help them get back into the "flow" of the procedure.



The MEDA Process Note: This article was published in Aero Magazine in the second quarter 2007 by William Rankin Ph.D. Boeing. Since 1995, Boeing has offered operators a human factors tool called the Maintenance Error Decision Aid (MEDA) for investigating contributing factors to maintenance errors. Boeing has recently expanded the scope of this tool to include not only maintenance errors but also violations in company policies, processes, and procedures that lead to an unwanted outcome. Boeing, along with industry partners, began developing MEDA in 1992 as a way to better understand the maintenance problems experienced by airline customers. A draft tool was developed and nine airline maintenance organizations tested the usefulness and usability of the tool in 1994 and 1995. Based on the results of this test, the tool was improved. In 1995, Boeing decided to offer MEDA to all of its airline customers as part of its continued commitment to safety. Since that time, the MEDA process has become the worldwide standard for maintenance error investigation. MEDA is a structured process for investigating the causes of errors made by maintenance technicians and inspectors. It is an organization's means to learn from its mistakes. Errors are a result of contributing factors in the workplace, most of which are under management control. Therefore, improvements can be made to the workplace to eliminate or minimize these factors so they do not lead to future events. EFFECT OF REDUCING MAINTENANCE ERRORS The 2003 International Air Transport Association (IATA) Safety Report found that in 24 of 93 accidents (26 percent), a maintenance-caused event started the accident chain. Overall, humans are the largest cause of all airplane accidents (see fig) Maintenance errors can also have a significant effect on airline operating costs. It is estimated that maintenance errors cause:

20 to 30 percent of engine in-flight shutdowns at a cost of US$500,000 per shutdown. 50 percent of flight delays due to engine problems at a cost of US$9,000 per hour, 50 percent of flight cancellations due to engine problems at a cost of US$66,000 per cancellation

More than 500 aircraft maintenance organizations are currently using MEDA to drive down maintenance errors. One airline reported a 16 percent reduction in maintenance delays. Another airline was able to cut operationally significant events by 48 percent. Many other operators have reported specific improvements to their internal policies, processes, and procedures.



In the early days of flight, approximately 80 percent of accidents were caused by the machine and 20 percent were caused by human error. Today that statistic has reversed Approximately 80 percent of airplane accidents are due to human error (pilots, air traffic controllers, mechanics, etc.) and 20 percent are due to machine (equipment) failures.



MEDA OVERVIEW Event. Decision. Investigation. Prevention strategies. Feedback. Event. An event occurs, such as a gate return or air turn back. It is the responsibility of the maintenance organization to select the error-caused events that will be investigated. Decision. After fixing the problem and returning the airplane to service, the operator makes a decision: Was the event maintenance-related? If yes, the operator performs a MEDA investigation. Investigation. The operator carries out an investigation using the MEDA results form. The trained investigator uses the form to record general information about the airplane, including when the maintenance and the event occurred, the event that began the investigation, the error and/or violation that caused the event, the factors contributing to the error or violation, and a list of possible prevention strategies. Feedback. The operator provides feedback to the maintenance workforce so technicians know that changes have been made to the maintenance system as a result of the MEDA process. The operator is responsible for affirming the effectiveness of employees' participation and validating their contribution to the MEDA process by sharing investigation results with them. The resolve of management at the maintenance operation is key to successful MEDA implementation. Specifically, after completing a program of MEDA support from Boeing, managers must assume responsibility for the following activities before starting investigations:

Appoint a manager in charge of MEDA and assign a focal organization.

Decide which events will initiate investigations.

Establish a plan for conducting and tracking investigations.



Assemble a team to decide which prevention strategies to implement.

Inform the maintenance and engineering workforce about MEDA before implementation.

MEDA PHILOSOPHY AND THE MOVE TO AN EVENT INVESTIGATION PROCESS The central philosophy of the MEDA process is that people do not make errors on purpose. While some errors do result from people engaging in behaviour they know is risky, errors are often made in situations where the person is actually attempting to do the right thing. In fact, it is possible for others in the same situation to make the same mistake. For example, if an inspection error (e.g., missed detection of structural cracking) is made because the inspector is performing the inspection at night under inadequate lighting conditions, then others performing a similar inspection under the same lighting conditions could also miss detection of a crack. MEDA began as strictly a structured error investigation process for finding contributing factors to errors that caused events. However, in the 11 years that MEDA has been in wide use. Boeing has learned that errors and violations both play a part in causing a maintenance-related event. An error is defined as a human action (i.e., behaviour) that unintentionally departs from the expected action (i.e.,behavior). A violation is a human action (i.e., behaviour) that intentionally departs from the expected action (i.e., behaviour). Today, MEDA is seen as an event investigation process, not an error investigation process. This new approach means that a maintenance-related event can be caused by an error, a violation, or a combination of an error and a violation. INCLUDING VIOLATIONS IN EVENT INVESTIGATIONS Violations are made by staff not following company policies, processes, and procedures while trying to finish a job - not staff trying to increase their comfort or reduce their workload. Company policies, processes, and procedures all can be violated. The revised version of MEDA acknowledges that violations have a causal effect, and they cannot be ignored if an airline is to conduct a complete investigation. The MEDA process distinguishes between three types of violations: routine, situational, and exceptional. Routine. These violations are "common practice." They often occur with such regularity that they are automatic. Violating this rule has become a group norm. Routine violations are condoned by management. Examples include:

Memorizing tasks instead of using the maintenance manuals. Not using calibrated equipment, such as torque wrenches. Skipping an operational test.



Situational. The mechanic or inspector strays from accepted practices, "bending" a rule. These violations occur as a result of factors dictated by the employee's immediate work area or environment and are due to such things as:

Time pressure. Lack of supervision. Pressure from management. Unavailable equipment, tools, or parts.

Exceptional. The mechanic or inspector will fully breaks standing rules while disregarding the consequences. These types of violations occur very rarely. CONCERING BOTH ERRORS AND VIOLATIONS Because errors have been the focus of much research, there are many more theories about why errors occur than why violations occur. However, errors and violations often occur together to produce an unwanted outcome. Data from the U.S. Navy suggests that:

Approximately 60 percent of maintenance events are caused by an error only. Approximately 20 percent of these events are caused by a violation only. Approximately 20 percent of these events are caused by an error and a violation (see figure )

In this example, a mechanic does not use a torque wrench (violation), which leads to an engine in-flight shutdown (event). There are reasons why (contributing factors) the violation occurred (e.g., unavailable torque wrench or work up norm is not to use a torque wrench).



In this example, the mechanic mistakenly misses a step in the airplane maintenance manual (contributing factor), which leads to an incomplete installation (error). The mechanic decides not to carry out the operational check (violation), thereby missing the fact that the task was not done correctly. Because an error was made and this was not caught by the operational check, an engine in-flight shutdown (event) occurs.





HOW ADDRESSING THE CONTRIBUTING FACTORS TO LOWER-LEVEL EVENTS CAN PREVENT MORE SERIOUS EVENTS A contributing factor is anything that can affect how the maintenance technician or inspector does his or her job, including the technician's own characteristics, the immediate work environment, the type and manner of work supervision, and the nature of the organization for which he or she works. Data from the U.S. Navy shows that the contributing factors to low-cost/no-injury events were the same contributing factors that caused high-cost/personal-injury events. Therefore, addressing the contributing factors to lower-level events can prevent higher-level events. In a typical event investigation, as conducted at many airlines in the past, a maintenance event occurs, it is determined that the event was caused by an error, the technician who did the work is found, and the technician is punished. Many times, no further action is taken. However, if the technician is punished but the contributing factors are not fixed, the probability that the same event will occur in the future is unchanged. The MEDA process finds the contributing factors and identifies improvements to eliminate or minimize these contributing factors in order to reduce the probability that the event will recur in the future. During a MEDA investigation, it is still necessary to determine whether the event is caused by human behaviour and find the individual(s) involved. Instead of being punished, however, the technician is interviewed to get a better understanding of the contributing factors and get the technician's ideas for possible improvements. The information can then be added to a database. The central part of the MEDA process is making the improvements needed to eliminate the contributing factors. Some of these improvements will be obvious after a single event and others will be apparent only after analyzing a number of similar events. After the improvements have been made, it is important to inform the employees so they know their cooperation has been useful



THE IMPORTANCE OF A DISCIPLINE POLICY It is important to have a discipline policy in place to deal with violation aspects of maintenance events. However, discipline or punishment is only effective for intentional acts. Boeing suggests a policy that:

Does not punish honest errors. Does not punish routine violations. Considers punishment for situational violations. Provides punishment for exceptional violations



Boeing supports the "Just Culture" concept, which is based on moving beyond a culture of blame to a system of shared accountability, where both individual and system accountability are managed fairly, reliably, and consistently. NEW MEDA MATERIALS AVAILABLE Boeing has updated the MEDA Results Form and User's Guide that reflect the process's new event investigation focus. These materials are provided to anyone at no charge. Boeing will also train operators at no charge if the training takes place in Seattle. SUMMARY Maintenance events have negative effects on safety and cost. A maintenance event can be caused by an error, a violation, or a combination of errors and violations. Maintenance errors are not committed on purpose and result from a series of contributing factors. Violations, while intentional, are also caused by contributing factors. Most of the contributing factors to both errors and violations are under management control. Therefore, improvements can be made to these contributing factors so that they do not lead to future maintenance events. The maintenance organization must be viewed as a system in which the technician is one part of the system. Addressing lower-level events helps prevent more serious events from occurring. For more information, please contact William L. Rankin at [email protected].



OTHER INVESTIGATION PROCESSES In addition to MEDA, Boeing has three other investigation processes available to the industry. Like MEDA, these tools operate on the philosophy that when airline personnel (e.g., flight crews, cabin crews, or mechanics) make errors, contributing factors in the work environment are a part of the causal chain. To prevent such errors in the future, those contributing factors are identified and, where possible, eliminated or mitigated. The additional investigation processes are:

Ramp Error Decision Aid (REDA), which focuses on incidents that occur during ramp operations. Procedural Event Analysis Tool (PEAT), which was created in the mid-1990s to help the airline industry effectively manage the risks associated with flight crew procedural deviations induced operational incidents. Cabin Procedural Investigation Tool (CPIT), which is designed for investigating cabin crew induced incidents

Part D Electrical Wiring Interconnection Systems


Important Information In this section will learn about the overall objectives of this module, general information about housekeeping practices in regards to wiring, and the causes of airplane wiring system degradation. The picture below shows the effects of debris contaminating an APU battery compartment. The debris fell onto the battery through a misaligned cabin air outlet grill. The debris was then charred by heat from the battery due to a shorted cell. Module Objectives

About Airplane

Wiring

Housekeeping

Causes of Wiring System Degradation



Module Objectives This module introduces and explains:

The causes of airplane wire harness degradation;

Contamination sources; Contamination protection planning; Contamination protection procedures; and Wiring system cleaning processes.



About Airplane Wiring Housekeeping

Maintenance practices and techniques vary greatly from company to company and from aircraft to aircraft. Improper maintenance can lead to as much damage to airplane wiring as extreme environmental factors. While each airplane consists of hundreds of thousands of individual wiring components, this module will look at the wiring system as a whole and explain how to prevent premature degradation of the system.

Air Transportation's (ATA) Specification 117 published in 1998 and manufacturer's guidelines. The guidelines in ATA Specification 11 7 are a compilation of manufacturer investigations and operator experience through continuing analysis and surveillance programs. This module identifies causes of airplane wiring degradation, and the internal and external sources of wiring contamination. It discusses practices and

procedures and how to clean as you go. The focus of this manual is to make the technician aware of the degradation impacts caused by improper maintenance practices and environmental factors. By knowing how, where, and why wire degradation occurs, technicians can prevent

The practices and techniques in this module are based on the 'findings of the Federal Aviation Administration's (FAA) Aging Aircraft program identified in the

techniques to protect equipment and wiring components during airplane maintenance and repair. It also explains how to plan prior to maintenance and repair

such damage and prolong the life of the wiring system. This decreases costly ground-time due to repair and maintenance and increases the productivity, serviceability, and profitability of the airplane.



Causes of Wiring System Degradation

There are many factors that cause premature degradation of the airplane wiring system components Although some of these factors cannot be prevented entirely, they can be limited through proper maintenance and repair practices. Most degradation of airplane wiring stems from the following: 1. Vibration 2. Moisture 3. Heat 4. Debris 5. Indirect damage 6. Chemical 7. Human contact

This section discusses how these factors occur and the practices and techniques used to prevent or limit these factors. The sources and prevention of contamination will be discussed in Section 2 in greater detail.



Vibration A leading cause of airplane wire degradation is vibration. It is often the result of improper clamp installation or maintenance. This leads to wire chafing and insulation cracking at clamping points. The wires or wire bundles not clamped properly rub against clamps, tie-wraps, or string ties and degrade the outer surface of the wire or insulation. This can result in damaged wiring and intermittent continuity. Vibration exacerbates any existing problems with insulation chafing or cracking.

Vibration Damage

Vibration can be reduced or eliminated by providing adequate support throughout the length of each wire or wire bundle. By using a sufficient number of supports and proper cable clamps, vibration can be significantly reduced and the life of wiring system components can be prolonged. The SWPM identifies the processes for replacing or installing wire harness supports in 20-10-12. It details the necessary conditions for clamp replacement, alternative replacement clamps, and the use of plastic tie straps, raceway clamps, and Stringer clips. In this Figure demonstrates how a Stringer clip attaches wire harnesses to the airframe stringers. The procedures for installing and removing these clips is found in the SWPM. Figure 1.5 demonstrates how loop clamps are used to attach the feeder wires on the CFM56-7B power plant of a Boeing 737.

Loop Clamps on Power Feeder Cables



Moisture Moisture accelerates corrosion of terminals, pins, sockets, and conductors. This leads to premature degradation. Moisture results from rain, snow, ice, condensation, cleaning, cargo spillage, galleys, lavatories, and damaged pipes and ducts. Corrosion is the deterioration of metals resulting from reactions between the metals and their environment. Galvanic corrosion requires a difference in electrical potential between an anode and a cathode (dissimilar metals), the presence of an electrolyte, and a conductive connection between an anode and a cathode. Corrosion occurs between dissimilar metals in contact with moisture because water serves as the electrolyte (Figure 1.6). A corrosion cell results in which metals become anodes and cathodes because of their relationship to each other in the electro-chemical series. The more active (anodic) metal will corrode in the process and the more passive (cathodic) metal will not. The relative size and degree of protection by finishes determines the rate at which corrosion takes place. Figure 1.7 identifies the reactivity of different metals in the galvanic corrosion scale. For design purposes, The Boeing Company classifies metals used

In airplane construction into four groups, with Group I being the most reactive and Group IV being the most passive or noble. The use of sealed connectors and proper routing of wires decreases moisture damage to sensitive components. However, moisture cannot be completely eliminated from the wiring system environment and corrosion is going to occur at some level in all aircraft. When this components are to be replaced according to the guidelines of the SWPM The most important strategy against corrosion is to implement a comprehensive corrosion prevention program for the airplane as a whole. A CPC program is now mandatory for FAR 121 operators

Galvanic Corrosion Model

A comprehensive program includes a minimum of the following: Washing for contamination removal. Cleaning the interior to assure drain paths and

valves are open.

Boeing Metal Reactiveness Scale

Cleaning of contaminants promptly. Applying and replenishing lubricants, water-

displacing compounds, and other corrosion inhibitors.

Protecting protective finishes and sealants during maintenance.

Inspecting systems thoroughly to identify conditions conductive to corrosion attack, such as breakdown in protective finish, to prevent corrosion before costly repairs become necessary.



Heat Exposure to high levels of heat can accelerate wire degradation and cause dryness and cracking of insulation. Even exposure to low levels of heat over long periods of time can damage wiring system components. Immediate damage to components can be caused by direct contact with any high level heat source. Improper replacement of high-temperature wire with low temperature wire, lack of separation between wiring components and heat sources, and failure to use correct insulation lead to premature wire degradation.

Heat Damage

Damage from high temperatures can be decreased or eliminated by protecting the components and/or separating them from heat sources. Engineering drawings and manufacturer's guidelines specify the minimum distances of separation between components and heat sources such as resistors, exhaust areas, and pneumatic ducts. However, not all wiring system components can avoid high temperature areas. In these cases, it is imperative that the correct wire type is used when replacing existing wire damaged by heat. The SWPM identifies replacement and alternative replacement wires by wire type code, wire specification, and airplane model in section 20-00-13 There are also several protective wire coverings to decrease the effects of high heat. This "sleeving" is found primarily in the power plant and APU areas. They are easily identifiable because they are made from fiberglass, metallic braiding, or conduit. This Figures snow two types of protective wire covers.



Metallic Debris or Swarf Wiring system components can be damaged by metal shavings, other debris from improper maintenance, and a lack of cleaning. Failure to protect these components during maintenance, and/or clean up following maintenance, causes long term problems and premature degradation. Routine cleaning will be discussed in Section 5 of this manual, so we will focus here on preventing debris caused from improper maintenance practices. Metal shavings and debris have been discovered on wire bundles after maintenance or repairs have been conducted. Airframe modification work produces a large amount of this debris. Proper protection and cleaning should be included into any maintenance or modification work plan. This will decrease the potential for damage to the wiring system, as well as components of any other systems in the airplane. Proper protection during maintenance or modification work requires good planning and attention to detail. These processes will be discussed in Sections 3 and 4 of this manual.

Debris Covered Terminals



Metal Shavings and Debris on Wire Bundles

Metal Shavings on Wire Bundle

Indirect Damage Damaged ducts, pipes, or other components can cause indirect damage to wiring system components. This damage may not be identified immediately, but leads to future problems. Failure to inspect and/or clean surrounding wiring components following damage to an apparently unrelated item causes premature degradation of the wiring system. Damage to any one component of any system can affect components of other systems. It is crucial that the technician conducts an inspection of the surrounding area following any damage that involves the spillage or leakage of fluids, gases, or debris of any kind.

Wire Harnesses Beneath Ducts

Chemical Contamination Chemicals such as hydraulic fluid, battery electrolytes, fuel, corrosion inhibiting compounds, waste system chemicals, cleaning agents, de-icing fluids, paint, and soft drinks cause premature wire harness degradation. The use of non-authorized cleaning agents also damage connectors, terminals, and splices. Although technicians have good intentions in cleaning these components, failure to follow manufacture's guidelines is harmful to the wiring system. Section 2 of this manual discusses the prevention of contamination in detail.

Chemical Damage



Human Contact Wire harnesses that remain untouched are less likely to degrade prematurely. Cleaning, inspection, repair, and other maintenance procedures often require wire harnesses to be moved, disconnected, or handled in other ways. However, the procedures that can cause further damage to wire harnesses are those that involve components and systems other than wiring. When technicians perform maintenance on wire harnesses, they are conscientiously being careful not to cause further damage. It is when they are performing maintenance on other areas/components that they tend to disregard the wiring system as they focus on the components being repaired, replaced, or inspected. This is when wire harnesses unconsciously become secondary to the procedure at hand and damage 0 to wire harnesses can occur Human contact with wire harnesses causes physical displacement and damage to wire harnesses. Wire insulation can be abraded or cut, splices and terminals can be loosened or stretched, connector contacts can be bent, and other potential damage can occur when humans and wiring interface. It is impractical to suggest that wire harnesses should not be contacted or handled during maintenance. Yet, it is possible to limit the physical displacement and damage that result from excessive and repeated contact. Technicians can decrease premature degradation by limiting how much they contact wire harnesses and

touching only the wiring components necessary to accomplish the specific task needed. Technicians must be aware of surrounding wire harnesses components and be careful not to lean against, pull on, step on, or hang things from these components. By making a conscious effort to prevent unnecessary damage to wire harnesses components, technicians can prolong the life of the wiring system.



Contamination Sources

In this section you will learn about the external, internal, and other sources of airplane wiring contamination. Each contamination source is accompanied by a model identifying the areas on the aircraft that damage occurs

External Sources Internal Sources

Other Sources

.



External Sources This section discusses the external sources of wiring system contamination. These are the sources that come from outside of the aircraft. The majority of these external sources come from nature. Air, rain, snow, and ice can damage and degrade wiring components. These elements cannot be prevented or avoided, but measures can be taken to decrease their effects. Another external source is de-icing fluids, which are directly related to the natural contaminants. Air can cause physical displacement of wiring components while the aircraft is in flight. Leading and trailing edges of wings contain wiring components that are usually well protected by panels, flaps, and slats. However, these components are exposed to air pressure and flow during take-off and landings due to flap and slat operations. The airflow can physically displace the components and cause vibration. Vibration, as discussed in Section 1, causes wires to become chafed and degradation is accelerated. Over the long life span of an airplane, continuous air flow can erode wiring insulation and can even unravel tie wraps and protective coverings. Air and the pressures caused by it are unavoidable. The damage it inflicts, however, can be decreased through a regular inspection program. The physical displacement of wiring components can be visibly inspected and the loosening of tie wraps etc. can be physically checked. The technician must ensure that inspection procedures are rigorously carried out and that these established company policies are adhered to.

Boeing 747 Wing



Rain can be a contaminant when the airplane is on the ground. Section 1 discussed the damage caused by moisture as it exacerbates corrosion. Rain is the leading cause of this moisture and is an unavoidable source of wiring system damage. However, rain also contains acidic pollutants such as sulphuric and nitric acids. These also accelerate corrosion and can damage wiring insulation. Rain also has another damaging quality when the airplane is in flight. It can be driven into open panels or into the leading and trailing edges of the wings with tremendous force. This causes physical damage to wires, connectors, and other components as the force of rain physically displaces them. Airplanes are designed to be self draining. Yet, it is the responsibility of the technician to ensure that all drain points are clear of debris and are working properly. Fresh-water rinses and routine washings can help to decrease the effects of the acids found in rain. Inspections of the wiring system components in the leading and trailing edges of the wings prevents any early stages of displacement or degradation from becoming a greater problem.

Wire Bundle Inside Wing Access Panel

Wire Bundle Under Wing Flap



Snow and Ice are also made up of the same elements of rain, so they can cause similar damaging effects. In addition, they can pack into the openings that rain can enter and then physically displace wiring components. When moisture freezes, it expands to further displace wiring components. The wiring components on an airplane are not affected by the extreme cold of snow and ice. These components are not damaged by the temperature, only the physical displacement and corrosion. Another risk of snow and ice comes during their removal and so the application of de-icing fluids will be discussed next.

Snow on Boeing 727

De-icing fluids remove snow ice, but can damage wiring components when applied carelessly. These fluids typically contain 30-50% monoproylene glycol, surfactants, and other chemical additives mixed with hot water. These mixtures are applied using high-pressure wands. The high pressures of de-icing fluids can cause physical displacement of wiring components. When sprayed into crevices in the airframe or wings, the pressure of these fluids can breakdown connector seals, backshells, and potting compounds. The de-icing mixture can also contaminate terminals and splices by exacerbating moisture corrosion. Technicians can decrease these effects by being careful not to spray fluids directly onto any visible wires, bundles, or other components. They also be very careful when spraying around any open panels or other places that may contain wiring components.

Application of De-icing Fluids



Internal Sources This section discusses the internal sources of wiring system contamination. These are the sources that come from inside the aircraft. Some of these contaminants are limited to specific locations such as cargo areas, galleys, or lavatories; some can be found throughout the aircraft. Most of these contaminants can be avoided by routine maintenance and inspections. It is the responsibility of the technician to ensure that these contaminants are controlled and that the wiring system components are protected.

New Wiring in Cargo Bay Floor

Cargo spillage can consist of anything from food and beverages to hazardous materials. The threat to the wiring system occurs when cargo spillage seeps into the floor joints in the cargo bay floor and onto the under-floor wiring. Any spillage can make the wires dirty and sticky. This leads to excessive build up of lint. dust, and other debris that is found in the under-floor. This affects the wiring, connectors, terminals, splices, and any other components it contacts. The primary protection against spillage is prevention. If spillage does not occur, then contamination is avoided. The technician must follow all company policies in regards to securing any cargo. The next prevention measure is to ensure that the cargo bay flooring is maintained and that all seals have not been damaged or breached. If spillage occurs, however, it is important that it's cleaned up immediately before it seeps to the under-floor or the contaminant spreads to other areas of the aircraft.



Hazardous materials must be properly identified and secured according to company policy. Chemicals such as mercury, battery spillage, and acidic chemicals can be extremely corrosive and damage any surfaces or materials they contact. Technicians must be knowledgeable of company hazardous materials handling procedures and follow them accordingly. In regards to the wiring system components, any spillage of hazardous material can have a variety of chemical reactions with metals in wiring, connectors, terminals, and all other wiring components. All airline companies have procedures for handling of hazardous materials as mandated by OSHA. The technician must be familiar with these procedures and follow them accordingly. The best protection from hazardous material spillage is prevention. If spillage occurs, ensure that all traces of the material are properly removed from the wiring components, as well as the rest of the airplane in accordance with company regulations.

Hazardous Materials Warning

Galleys and lavatories are hotspots for spillage. Beverages such as soda, alcohol, and coffee that contact the wiring components can accelerate corrosion, degrade wiring, and increase build up of lint, dust, and debris. Lavatory fluids such as "blue water", sanitizers, urine, and other waste also cause similar effects and can be even more corrosive. The primary protection for these types of spillage is also prevention. If spillage does not occur, then contamination is avoided. However, the technicians responsible for the maintenance of wiring has little control over the actions of flight-crew members or other passengers on the airplane Technicians, therefore, must expect that spillage will occur and take prevention to the next level.

Typical of Galley

That next level is to prevent any spillage from contacting the wiring system components. To do this, make sure that all floorings around galleys and lavatories are properly sealed and maintained. Inspect toilets, sinks, and containers for any leaks. Verify that proper maintenance and servicing has occurred. Clean up any spillage immediately and inspect any wiring components contacted



Lint and dust are electrostatically attracted to all wiring system components and are found throughout the aircraft. They do not cause damage directly to the components, but they can lead to two conditions that are dangerous to the wiring system. Excessive build-up of lint and dust creates a fire hazard much like any other flammable material would be if it covered components carrying electrical charges. This build-up also attacks moisture that can accelerate corrosion. All contact with lint and dust can be avoided, but technicians can prevent excessive build-up by establishing and following a regular cleaning schedule. Section 4 of this manual details the processes involved in wiring systems cleaning.

Lint and Dust Covered Connectors

Engine and APU oils are synthetic oils that leak from the engines and APU and are deposited on surrounding wiring components. These oils soak and penetrate wiring insulation and deteriorate the wiring over time. They cause connector seals to swell and then they penetrate into connectors to damage the connectors. They cause corrosion, intermittent shorts, and even failure of pin-retention devices resulting in complete failure of the connector and system components. These oils also deteriorate rubber clamps by causing cracking and swelling, and they cause heat-shrink protectors to lose their "shrink".

Repairing all leaks, inspecting breather outlets, and wiping up cowls can decrease damage from engine and APU oils. All wiring components exposed to these oils should be cleaned immediately and inspected for any additional damage.

Contaminated APU Wiring Components



Hydraulic oils found on modern commercial aircraft are normally phosphate esther synthetic oils under the generic name of Skydrol. They cause damage similar to engine and APU oils, and deteriorate everything they contact, with the exception of Teflon and aluminum. These oils come from the leakage of hydraulic system components found in the tailplane, wings, hydraulic pumps, and landing gear areas. They deteriorate clamps, seals, potting compounds, and insulation faster than most other contaminants. They cause failure of connector seals, inserts, and pin-retention devices. They deteriorate labels and decals making proper identification of components difficult. These oils will basically deteriorate everything they contact over time and can cause damage to the entire wiring system.

Wire Bundle Near Hydraulics

Technicians should consult company policies in regards to cleaning

up hydraulic oils and be sure to clean up any spills or leaks immediately.

Fuel consists of mineral-based hydrocarbons that remove all natural oils present on components it contacts. It causes drying, staining, and cracking of wiring insulation and removes protective treatments on wiring components. It causes connector seals to swell and then penetrates into the connectors to cause failure of pin-retention devices. Fuel also removes any anti-corrosion treatments that have been applied to wiring components.

Technicians can prevent damage to wiring components caused by fuel by repairing any fuel leaks immediately and routing fuel lines below wiring components as required, and checked against the airplane installation configuration drawings



Grease is a mixture of oil and metallic powder (lithium). It seeps out of bearings and can be deposited on wiring components. Grease causes damage similar to oils. It penetrates wiring insulation and causes the wiring to deteriorate over time. It causes connector seals to swell and then leads to damage of the connector and pin -retention devices. By following correct greasing procedures and wiping off extra greases, the technician can limit the amount of grease that is deposited

Wing Component Located Beneath Grease Sourse

Bleed air can be damaging to wiring system components. It is used for cabin conditioning, de-icing, and for starting the engines on aircraft. The heat from the engine compressor can be above200 degrees Celsius. If wiring components are too close to the bleed air ducts, the heat can damage wires, connectors, and other components. The bleed air ducts are located around the engines and the APU. Even wiring components that are not close enough to exhibit immediate and visible damage from the heat can sustain damage from low levels of heat over a long period of time. Technicians can prevent heat damage from bleed air by conducting routine inspections of wiring and ducts. Any wiring that has been damaged should be replaced immediately to prevent consequences that can be both dangerous and costly.

Wiring Components Near Bleed Air Ducts



Other Sources This section discusses other sources of wiring system contamination that does not fall neatly into the categories of external or internal. These sources can be found both inside and outside of the aircraft depending on the situation. Like de-icing fluids, they are contaminants that are introduced by technicians during maintenance procedures, or come from a source that is in the aircraft's environment. Because most of the wiring is found inside the airplane, many of these sources will affect mostly the internal components. These external contaminants are maintenance provided and have been introduced to the environment under other-than-normal conditions.

Various External Paint Designs



Paint can be found both inside and outside of the aircraft, but the primary point of damage to the wiring systems is found in the wheel wells. Most airlines repaint the exteriors of their aircraft every four to five years, and usually during C-checks or D checks. Paint is not usually damaging to wiring components directly. It can, however, obscure or completely cover markings making maintenance difficult and more time intensive. Paint contacts the wiring components through over spraying or dripping when technicians fail to properly mask-off areas that should be protected. The components most susceptible to damage when painting the aircraft's external body are those located in the wheel-wells and wing edges. The other damage that results from painting comes during cleaning or paint removal from wiring components.

Paint stripper is a caustic alkaline chemical that causes similar damage as hydraulic oils. It deteriorates seals, clamps, potting compounds, and insulation. These lead to failure of connector seals, inserts, and pin retention devices. It also erodes labels, decals, or other identification markings that makes maintenance procedures more difficult. The best prevention of paint contamination is to mask-off the surrounding areas with a protective film, plastic, or paper to eliminate any airborne pain/stripper particles from contacting wiring or other essential components that are susceptible to corrosion or damage. It is important for the technician to remember that stripper is dispersed through the air, and that the area of possible contamination is not limited to the immediate area where the stripper is being applied.

Safety precautions call for good ventilation of a stripped area, and this can cause the particles to be dispersed even farther from the immediate site. Technicians must evaluate the conditions of each situation before application begins.



Debris or swarf consists of small particles of metal debris caused from aircraft modification or other maintenance. These particles can be aluminium, magnesium, steel, copper, or any other metal and are usually very sharp and can be corrosive. Refer to Section 1 and the galvanic corrosion scale. When dissimilar metals come in contact, the more active of the metals will corrode. When steel shavings from an airframe modification fall onto copper or aluminium wiring components, corrosion occurs. If this happens in a moisture-rich environment, or if the particles are not cleaned up and the area becomes wet, then corrosion will be accelerated and the wiring components will become damaged. Swarf also causes penetration of wiring insulation because drill shavings are sharp and cut the insulation. This leads to shorts in the wiring. Swarf can also cut, penetrate, and short connectors, terminal, and splices. It can also cause damage to LRU components by entering the units ventilation system and causing shorts or even physical damage to its internal components. Swarf can be prevented by protecting surrounding areas and implementing a "clean as you go" philosophy. Masking off surrounding area when performing modifications or other maintenance procedures can protect against these small particles contacting wiring components. Remember that these particles can also be small enough to be transferred by air, so evaluate each situation before proceeding and isolate the repair to the working area. The Cleaning section 4 will discuss the "clean as you go" principles in detail.

Wire Bundles Contaminated with Swarf



Foreign objects can damage wiring components easily. Tools, screws, washers, rivets, and other metallic objects can cause shorts and physically damage wiring components. Physical damage can be displacement, penetration or cracking of insulation and components. It can be caused when objects are dropped on components or during flight when objects are not cleaned up. Foreign object damage (FOD) leads to $4 billion in damages to the aerospace industry each year. FOD control is vital to any maintenance procedure. Each technician and line supervisor is responsible for reducing damage to aircraft components caused by FOD. Every company should have a FOD prevention and control plan. This plan should include control and accountability of all tools, parts, and equipment. Tool and equipment cards, parts lists, containment trays, and tool identification measures help to ensure accountability during maintenance. Regular inventory inspections should be performed during procedures and again when maintenance is completed. FOD walks through the interior and around the exterior of the aircraft help technicians to ensure all items are gathered when main ten ace procedures are completed

FOD in Cargo Bay

Cargo Bay of Freighter



Animal waste is extremely corrosive and can cause damage to wiring components. It consists of uric acid and fecal matter. It causes similar damage as spillage from lavatories, but can be even more corrosive. Spillage from frozen fish and other meats also fits into this category. Freighters are more susceptible to this type of damage by the sizes of their cargo, as well as, the types of animals they transport. The key to limiting the corrosive effects of animal waste is prevention

Technicians should protect as much of the aircraft interior as possible, especially insulation blankets if conditions permit. Insulation blankets absorb moisture and must be dried out during refurbishment. The stowage areas must be ventilated when the aircraft is on the ground to decrease build-up of moisture and heat. Watertight floorings and sidewall coverings with absorbent material should be installed to contain the waste. Consult the company policies in regards to transporting animals and related maintenance



Contamination Protection Planning

In this section you will learn how to develop planning measures for the protection of aircraft wiring systems during maintenance procedures.

Protection Planning Overview

Elements of a Protection Plan

Protection Plans

Area Mapping



Protection Planning Overview The first step in any maintenance, repair, or modification procedure is planning. A comprehensive plan for these procedures must include the protection of surrounding components. Protecting the wiring system reduces contamination from FOD and swarf caused by machining. Developing a protection plan can eliminate the time and costs associated with contamination cleanup, as well as, repair or replacement of damaged wiring harness components.



Elements of a Protection Plan

A protection plan should contain the following elements: 1. Identification Identify the location of any

components that could potentially be damaged.

2. Initial Cleaning

Remove any existing debris or contaminants from components so as to allow firm adhesion of adhesive tapes holding plastics or papers in place to allow the QUARANTINE of areas.

3. Protection Cover all components in the surrounding area. This can be done by masking off the area with paper or plastic sheeting. It is important that all components are properly covered and that the ends of the sheeting are secured with tape. The sheeting should extend beyond the immediate area where maintenance or modifications are being performed because small particles become airborne and can be distributed to areas outside the initial workspace

4. Follow-up Cleaning Remove any contaminants or debris from the work area during and after the maintenance or modification work has been completed. "Clean as you Go" The paper or plastic sheeting should be cleaned prior to being removed. It should be treated as a work surface and cleaned accordingly.

5. Protection Removal After the sheeting has been cleaned, then it can be removed. It is to be rolled or folded from the outside edges inward this will cause any contaminants or debris missed during the follow up cleaning to be trapped within the sheeting. The sheeting can be used again for future projects after it has been properly cleaned and all debris has been removed.

6. Inspection

Before the project can be deemed complete, the area must be inspected. Even the most comprehensive debris prevention efforts can sometimes fail. The area must be inspected for any debris or contamination that may have broken through the defence of the prevention plan and contaminated the airplane wiring system.



Protection Plans

A plan to protect wiring system components from contamination is dependant on the procedure being performed. Most maintenance, repair, or modification procedures require their own set of measures based on the six elements of protection planning. The focus of this topic is to make technicians aware of the different planning aspects in relation to specific types of maintenance. The details of the procedures used to protect the wiring components will be discussed later in this section. The location of the procedure will determine the area and type of protection needed. Typically, maintenance procedures performed inside the aircraft require more extensive masking of surrounding areas. Whereas, procedures performed outside require less masking, but more initial cleaning. Procedures in the upper portion of the fuselage requires consideration as to where debris will fall. Care must be taken to prevent swarf from entering into ventilation ducts and other sensitive areas. If milling or grinding procedures are being performed, it is recommended that vacuum collection is used. Procedures in the lower portion require emphasis to protect wiring system components that are in close proximity to machining operations because the majority of electronic equipment is fitted below floor level. On the Figure shows some of the specific areas of focus in different protection plans. Technicians can use this chart as a guide to developing their own protection plans for other maintenance procedures.

Protection Planning Variable Chart



Area Mapping Area mapping is the process of dividing the aircraft into specific sections or "zones" and identifying the wiring system components located within each zone. As discussed in Module C, zonal identification helps to focus attention to a specific area, rather than viewing protection of the entire wiring system as one enormous and overwhelming task. Aircraft are divided into eight major zones. Each zone (except 500 and 600) contains different wiring harness components. Figure 3.3 shows the primary wiring system components that are at risk in each major zone. Technicians must protect these components during maintenance procedures.

Airplane Major Zones

Primary Wiring Components in Major Zones



Contamination Protection Procedures

In this section you will learn how to protect aircraft wiring systems during maintenance procedures. These procedures include: General maintenance

Airframe repair and modification

Powerplant repair and

Modification



Protection Overview The key to preventing premature degradation of wire harnesses is protection. In this section of this Module explains the planning process, but this section explains the practices used to physically protect components during maintenance. The focus of protection is to prevent contaminants from contacting wire harnesses. As discussed in earlier sections, these contaminants can be fluids, vapours, or solid objects. Fluids can be aqueous or oil-based, vapours can be seen or unseen and solid debris can be large or microscopic. Protection procedures are based on the type of potential contaminants in each situation. The location of the maintenance procedure also effects protection procedures. Spillage, machining debris, and other contaminants can cause more damage in some areas than in others so they pose a greater hazard in certain situations. Access to maintenance areas is also a factor in contamination protection. Small areas limit the maneuverability of technicians and make it difficult to perform protection measures for the surrounding wire harnesses. The procedures in this section are not feasible in all situations. They are recommendations for "best practices". They are not based on existing regulations or requirements. They are a compilation of ideas and practices to help technicians prolong the life of wire harnesses and the airplane. The protection procedures are grouped into three categories: General maintenance Airframe repair and modification Power plant repair and modification.



General Maintenance

These steps are designed to protect wire harnesses during routine maintenance procedures. Their purpose is to prevent contaminants from contacting wire harnesses. They can be used anywhere on the airplane but must be tailored to fit each situation based upon type of contaminants, location, and access to the working area. General maintenance procedures include cabin re-configuration, LRU replacement, servicing, and other routine maintenance that exposes wire harnesses to possible damage or contamination.

1. Initial clean of existing lint and debris from area and wire

harnesses using proper techniques and materials. 2. Cover surrounding components by draping cloths, plastic

sheeting, or draperies over components to protect from spillage or debris. In most situations, it is not necessary to wrap each wire harness individually. Loosely draping a large area is usually adequate to prevent contamination from contacting wire harnesses.

3. Cover open connectors with antistatic caps, wrap them in plastic

sheeting or put them in plastic bags secured with rubber bands, and then secure them to the airframe with ties. This prevents contaminants from getting in to contact cavities, seals, and other parts of connectors. Securing them to the airframe prevents potential physical damage 0 that could occur if the connectors were left hanging.

4. Secure any hanging wires to the airframe using ties. The ties

should be close enough to prevent the wires from being physically displaced and wire bundles from separating. If long portions of wires or bundles are to be coiled and stowed,

be sure to allow a sufficient bend radius of coils. Coils must have a bend radius of at least 10 to 1

This means that the diameter of the coil must be no less than 10 times the thickness of the wire or wire bundle.

5. Inform other technicians of any loose wire harnesses in the

working area. This can be done verbally, by posting signs, using marking tapes, or any other method that identifies that components are susceptible to damage.

6. Do not use overhead wire harnesses for support. Wire bundles

can be physically displaced if used as a hand rail or used to support drop-lights or other tools.

7. Reinstall clamps to correct specifications. Be sure that wires are

not pinched in clamps. This will cause failure of the insulation layer, causing a short to ground.

8. Conduct maintenance in accordance with SWPM guidelines and

use only the tools, materials, and procedures identified in the corresponding SWPM subject for each component.



Airframe Repair and Modification

These steps are designed to protect wire harnesses from the large quantities of swarf produced during airframe repair and modification procedures. These sharp metallic particles can be very damaging to wire harnesses because they can cause shorts, cut wire insulation, and accelerate corrosion. The purpose of protection is to prevent swarf from contacting wire harnesses. The steps identified under general maintenance are applicable for airframe maintenance with the exception of covering surrounding components. The loosely draping of harnesses used for general wire maintenance procedures is not adequate to protect components from the swarf production during airframe repairs and modifications. Apply these steps when performing airframe work. Be sure to tailor them to fit each situation and work area.

1. Select a material to curtain off the work area. Plastic sheeting should be

used rather than cloths or draperies because the sharp metallic particle is not as likely to stick to plastic as it is to other materials. The thickness of the plastic sheeting is determined by the type of work being performed. Drilling requires thicker sheeting that sanding because of the particles produces. The size of the sheeting is determined by the location or area the work is being performed in. The sheeting must be large enough to separate the work area from all other areas of the airplane.

2. Curtain off the work area. Secure the sheeting by taping it to the

airframe. Do not use masking tape because it is difficult to remove if it is in place for extended periods of time. It is best to use duct tape, blue tape, or electrical tape because they are less likely to adhere to surfaces so they are easier to remove after the work is complete. The tape should be used on the entire perimeter of the sheeting to prevent airborne particles from penetrating around the edges of the sheeting. If more than one piece of plastic sheeting is used, they should be overlapped to prevent excessive separation. This overlapping area can be used as a point of entry in to the work area. If this is the case, the sheeting should be overlapped enough to allow personnel to enter or leave the work area without permitting contamination to escape into other areas.

3. Wrap all wire bundles in the work area. When working on the airframe,

It is usually not possible to cover all wire harnesses with sheeting because many of the wire harness run along the airframe itself and are

close to the portion of the airframe that is being repaired. In this case, wrap bundles individually so that the airframe can be accessed and the wiring is protected.

4. Use vacuum extraction when performing maintenance. This limits the

amount of swarf available to contaminate surrounding components. It reduces the amount of microscopic particles that become airborne and decreases particles on the ground that can be tracked into other areas.

5. Limit the amount of personnel entering the work area. Provide alternative

access to other areas if the work area is centrally located in the aircraft. This decreases the amount of swarf that is tracked into other areas.

6. Provide debris removal areas just outside the curtained off area. These

areas should have plastic sheeting on the floor, brushes for clothing and shoes, and vacuum extraction equipment. A debris removal area should be located at each entry point into the work area. This allows personnel to remove any swarf that can be tracked into other areas.

7. Perform routine cleaning of the work area and debris removal areas. Cleaning should be done before maintenance starts, at the end of each shift, and when maintenance is complete. Use the cleaning procedures explained later in this module



Powerplant Repair

These steps are designed to protect wire harnesses from being damaged during power plant repairs and engine changes. Their purpose is to prevent oils and fuels from damaging wire harnesses. In most circumstances, contamination contacting exterior wiring components such as wire insulation and connectors is unavoidable, but internal components such as connector contacts and wire conductors can be protected The wire harnesses in the engine areas are more susceptible to damage from heat and vibration than in any other section of the airplane. Technicians must use care when moving or handling these wire harnesses. They must physically inspect these wires, connectors, splices, and other components for cracking, breaks, worn surfaces, and other damage caused by the extreme heat and vibration, as well as oil and fuel contamination.

1. Cover surrounding components by draping cloths, plastic sheeting, or draperies over components to protect from oil spillage. Be sure to wait until the engine is cool enough to touch so that the sheeting is not melted by the heat of the engine.

2. Cover open connectors with antistatic caps, wrap them in plastic

sheeting or put them in plastic bags secured with rubber bands. Some wire harnesses are part of the engine and should be secured to it. The wire harnesses that are part of the airplane must be secured out of the way when the engine is being changed. This prevents damage to the wire harnesses when the new engine is installed. Cover both sets of open connectors to prevent debris or oil from contaminating contact cavities, seals, and other parts of connectors.

3. Do not bend the main power feeder cables after disconnecting them

from the engine. They are thicker than most other wires and are not as flexible. They should be secured to the nearest cowl using ties. Their terminals should be inspected for corrosion, heat damage, distortion, and general serviceability.

4. Cover engines when working above them. Machining work on pylons and wings can cause swarf and other debris to fall on or in the engine. Use intake and exhaust covers to protect the internal components of the engine and plastic sheeting to protect the external components. It is also advisable to close the cowls when working above the engine. Whenever possible, do not perform maintenance above the engines at the same time engine work is being performed.

5. Take care with the fire protection system components. The sensors

are semi-rigid and made of stainless steel. The have limited flexibility and can be easily damaged if moved. Fire wire connectors must be protected the same as other connectors and they must be dry and free of any grease or oil before being reconnected.

6. Clean as you go.



Cleaning Procedures

In this section you will learn the cautions and warnings, the materials, and the procedures used to clean aircraft wiring harness components. The Cleaning Process Cautions and Warnings Cleaning Materials Cleaning Procedures Matrix Cleaning Procedures



The Cleaning Process

The cleaning of wire harnesses and other electrical equipment is a crucial part of aircraft maintenance. It is impossible to perform adequate inspections or repairs on components that are covered with contamination. Yet, improper cleaning techniques can cause damage or physical displacement of components that are in good working condition. This has been a controversial subject in the field of wiring system maintenance and must be addressed. Cleaning is performed based on situational necessity. Wire harness components are not cleaned simply because they are dirty. They are cleaned when they must be repaired or inspected. This is because the cleaning process is time and labour intensive and can also cause unnecessary displacement or damage. Thorough cleaning is usually performed during heavy checks (B, C, or D checks) because wire harnesses are being inspected and maintenance is being done. Lighter cleaning is usually performed during A or B checks because less inspection or maintenance is needed. Cleaning is seldom performed when an airplane is operational unless inspections or repairs are necessary. The level of cleaning and materials used are determined by the type and extent of contamination. Heavy contamination of corrosion or debris requires more cleaning than a light coat of oil or other fluids. The proper materials and techniques used for various levels and types of contaminants are outlined in this section. Care must be taken to make sure that the cleaning process does not cause further damage to wire harness components. Wire harnesses must be supported when clamps are removed. Applicable Cautions and Warnings must be followed during cleaning and all repairs must be carried out in accordance with the SWPM, unless permission from the OEM (Original Equipment Manufacturer) has been obtained.

Bundles must be properly reassembled after cleaning has been completed and system checks must be carried out to verify the integrity of individual systems. The cleaning procedures and materials in this section are based upon those found in the SWPM. Additional information and regulations may be instituted by individual companies if they are in accordance with regulatory bodies.



Cautions and Warnings

The following list of cautions and warnings apply to cleaning procedures. They are divided intro three categories 1. Personal Protection 2. Components protection 3. Fire protection



Personal Protection 1. The following protective equipment should be used: Aprons Boots Coveralls Neoprene gloves Rubber gloves Chemical goggles Approved eye protection

2. To make sure that solvent vapors are not breathed, one of these conditions should occur: The area has a good air flow Respiratory protection is used

3. The cleaner manufacturer's conditions must be obeyed 4. The local necessary conditions must be obeyed. 5. Compressed gas can be dangerous. To prevent an injury, carefully apply the gas in the direction away from the eyes, face, and other personnel. 6. Do not separate the connectors until the temperature is sufficiently cool enough, approximately 100 degrees F (28 degrees C), to touch with bare hands.



Component Protection 1. All connectors in the area must be protected. 2. Equipment or components that are sensitive to contamination, solvents, or water must be protected if they are near the area that is to be cleaned. 3. An aqueous cleaner must only be mixed at the recommended concentration. 4. A solvent, a cleaner, contamination, or water must not go into a connector. 5. A paint, a plastic, a polymeric material, or an adhesive must be fully cured before it can be cleaned 6. When using a solvent, these conditions apply:

o A solvent must not be mixed with a different cleaner o The solvent must be approved for cleaning the materials in a wire harness o The local environmental conditions must be obeyed o The solvent must only be applied as it is permitted or specified in the cleaning procedure

7. When using an aqueous cleaner, these conditions apply: o The pH of the cleaner must be a maximum of 9.0 o The area to be cleaned must have sufkient drainage for large volumes of liquid o The cleaner must not be mixed with other cleaners o The solvent must be approved for cleaning the materials in a wire harness o The local environmental conditions must be obeyed o The cleaner must only be applied as it is permitted or specified in the cleaning procedure o

8. When using a wiper, these conditions apply: o Do not put too much aliphatic naptha or isopropyl alcohol on the wiper. o Do not use more water than is needed to make the wiper moist. o Do not put too much solvent on the wiper. o

9. Do not use a solvent that is not specified for use with the materials and the components in a wire harness 10. Do not move a wire harness more than is necessary to clean it.



11. Do not clean a wire mark or an identification tape with too much force. 12. Carefully clean the contamination on protective finishes. 13. Do not get aliphatic naptha on control cables, acrylic, decals, or finishes that are not resistant to Skydrol (BMS 3- 11) or on a surface that has a corrosion

inhibiting compound on it, as they will be removed. 14. Do not let aliphatic naptha stay on a wire harness component longer than three minutes 15. Do not put the flow of cleaning fluid or water closer than six inches from a connector. 16. Make sure that the surfaces are flushed sufficiently to remove all of the cleaner, 17. The connector must be fully dried before the plug can be installed. 18. Do not put silicon lubricant on the connector insert or the contacts.



Fire Prevention 1. A flammable solvent must be kept in an approved closed container. 2. Methyl alcohol and isopropyl alcohol are flammable. Make sure that the quantity of isopropyl alcohol near the airplane is no more than is necessary to

clean the wire harness. 3. A wiper or cloth made with a synthetic material is not permitted because a synthetic material may make an electrostatic discharge. 4. These conditions are applicable in an area where flammable solvents or vapours are present:

o All flames, smoking, sparks, and other sources of ignition must not occur o Tools that are used must not make sparks o Clothing, materials, or processes that can make electrostatic discharges must not be used o All electrical equipment, such as lights, motors, wiring, etc., must meet the necessary electrical and fire codes o The accumulation of vapours must be prevented by sufficient ventilation o Flammable solvents must be kept in closed containers



Cleaning Materials





Cleaning procedure Procedure 1 Materials Aliphatic naphtha Isopropyl alcohol Wiper or a cloth Contamination Removal 1. Disassembly of Wire harness

Remove all wire harness ties in the area of the contamination. Separate the wires.

2. Remove contamination using aliphatic naphtha. Put sufficient quantity of aliphatic naphtha on a wiper to make it moist. Use a moist brush to loosen particles if necessary. Wait a maximum of three minutes for the aliphatic naphtha to loosen the contamination. Dry the remaining solvent that is on each wire harness component with a clean wiper or use carefully applied 10 PSI compressed air or nitrogen. Repeat until all contamination is removed.

3. Remove all remaining aliphatic naphtha contamination from wire harness components. Put sufficient quantity of isopropyl alcohol on a wiper to make it moist. Carefully clean the aliphatic naphtha contamination from each component with the moist wiper. Dry the remaining isopropyl alcohol that is on each wire harness component with a clean wiper or use carefully applied 10 PSI compressed air or

nitrogen.



Procedure 2 Materials -Aqueous cleaner .Brush -Wiper or cloth Contamination Removal

1. Disassemble the wire harness. Remove all wire harness ties in the area of the contamination. Separate the wires.

2. Remove contamination using an aqueous cleaner. Make a mixture of cleaner and water that has a pH level of 9.0 or less. Apply the water and cleaning solution on the wire harness using a hose, wiper, or brush. Let the cleaner soak for approximately five minutes making sure that the cleaner does not dry on the surface of a component. Use a moist brush or wiper to loosen particles if necessary. Rinse the area with clean warm water that is 160 degrees for less. Dry the wire harness component in the air, with a clean wiper, or carefully applied 10 PSI compressed air or nitrogen.

3. Inspect the wire for contamination. 4. Refer to Procedure I if contamination cannot be removed with the Aqueous cleaner and water.



Procedure 3 Materials Brush Vacuum Wiper or cloth Isopropyl alcohol (if necessary)

Contamination Removal 1. Remove loose particles that are on the external surface of the wire harness using hands, brush, vacuum, or wiper. 2. Disassemble the wire harness. Remove all wire harness ties in the area of the contamination. Separate the wires.

3. Remove the remaining contamination using water. Put sufficient quantity of water on a wiper to make it moist. Carefully clean the contamination from each component with the moist wiper. Be sure to clean the areas where contamination can be caught (clamps, sleeves, etc.). Dry the wire harness component with a clean wiper or carefully applied 10 PSI compressed air or nitrogen.

4. Inspect the wire for contamination. 5. If contamination cannot be removed using water, remove contamination using isopropyl alcohol. Put sufficient quantity of water on a wiper to make it moist. Carefully clean the contamination from each component with the moist wiper. Be sure to clean the areas where contamination can be caught (clamps, sleeves, etc.). Dry the wire harness component with a clean wiper or carefully applied 10 PSI compressed air or nitrogen. Repeat until all contamination is removed.



Procedure 4 Materials Water Wiper or cloth

Contamination Removal 1. Disassemble the wire harness. Remove all wire harness ties in the area of the contamination. Separate the wires.

2. Remove contamination using water. Put sufficient quantity of water on a wiper to make it moist. Carefully clean the contamination from each component with the moist wiper. Be sure to clean the areas where contamination can be caught (clamps, sleeves, etc.). Dry the wire harness component with a clean wiper or carefully applied 10 PSI compressed air or nitrogen.

3. lnspect the wire for contamination. 4. If contamination cannot be removed using water, remove contamination using isopropyl alcohol. Put sufficient quantity of water on a wiper to make it moist. Carefully clean the contamination from each component with the moist wiper. Be sure to clean the areas where contamination can be caught (clamps, sleeves, etc.). Dry the wire harness component with a clean wiper or carefully applied 10 PSI compressed air or nitrogen. Repeat until all contamination is removed.



Procedure 5 Materials Brush Vacuum Wiper or cloth

Contamination Removal Remove contamination using brush, vacuum, or wiper. Be sure to clean the areas where contamination can be caught (clamps, sleeves, etc.). Procedure 6 Materials Isopropyl alcohol Brush Swab Wiper or cloth

Contamination Removal 1. Disassemble the wire harness. Remove all wire harness ties near the end of the connector. 0 *Separate the wires. 2. Remove the backshell. 3. Remove contamination from grommet, backshell, and wire near the connector using isopropyl alcohol Carefully apply isopropyl alcohol with a brush or swab. Clean the area until contamination is dissolved. Flush the area with sufficient quantity of alcohol to remove contamination. Repeat until all contamination is removed. Dry the connector in the air for one hour or carefully applied 10 PSI compressed air or nitrogen.

4. Seal any empty contact cavities.



Procedure 7 Materials Isopropyl alcohol Swab Wiper or cloth

Contamination Removal 1. Disassemble the wire harness. Remove all wire harness ties near the end of the connector. Separate the wires.

2. Remove the backshell. 3. Remove contamination from backshell, front and rear inserts, and wire near the connector using isopropyl alcohol Put sufficient quantity of water on a wiper to make it moist. Carefully clean the contamination from each component with the moist wiper. Repeat until all contamination is removed



Procedure 8 Materials Isopropyl alcohol or methyl alcohol Brush Swabs


2. Separate the plug and receptacle. 3. Remove contamination using isopropyl alcohol or methyl alcohol. Carefully apply alcohol with a brush or swab. Brush the face of the connector until contamination is dissolved. Flush the face of the connector with sufficient quantity of alcohol to remove contamination. Dry the connector in the air for one hour or carefully applied 10 PSI compressed air or nitrogen. Put the connector in a position so that it is not fully on its side to let the solvent drain.

4 Inspect the wire for contamination. 5. Refer to Procedure 9 if contamination cannot be removed using isopropyl alcohol or methyl alcohol, or if a fast turnaround is necessary.



Procedure 9 Materials 0.25 pint (0.125 Litter) of acetone Squeeze container Brush Swabs Container of the sufficient size to catch solvent


2. Separate the plug and receptacle. 3. Remove contamination using acetone. Put 3 cc to 5cc of acetone into the connector with the squeeze container. Brush the face of the connector until contamination has been loosened. Remove the unwanted acetone in the container from the work area. Flush the face of the connector with no more than 5 cc of acetone to remove contamination making sure to catch the acetone with another container. Remove the unwanted acetone in the container from the work area. Repeat until all contamination is removed. Dry the connector in the air for one hour or carefully applied 10 PSI compressed air or nitrogen making sure the inside of the socket contacts and

inserts around them are fully dry.

Part E Electrical Wiring Interconnection Systems


Aircraft Wire or Cable



This module introduces and explains:

- Typical damage found; - Electrical bonding and grounds.



Typical Damage of Wire and Wire Bundles

In this section, Typical Damage of Wire and Wire Bundles, you will learn the typical insulation damage found and how that damage can occur on wire and wire bundles.

Insulation Damage

Abrasion

Heat Damage

Fluid Damage

Nicks, Scrapes and

Maintenance Damage

Carbon Arcing



Insulation Damage Although the wiring that was originally installed in today's aircraft is a superior product, long aircraft life combined with sometimes careless maintenance practices have taken their toll on the wiring systems. One of the first places that normally are damaged is in the damage to insulation. Following you will see some examples of typical insulation damage. The most common forms of damage are caused by: abrasion (chafing), heat, fluid damage of all types, nicks, scrapes and maintenance damage, over bent radii, corrosion, impact with cargo and passengers, being used as hand-holds and exposure to the elements

Abrasion (Chafing) The first type of typical damage to be shown will be from chafing, or the rubbing of wires against one another, dissimilar wires or structural members, to include flight controls. Abrasion and heat damage caused by wires that had chafed against each other and against the duct. The heat damage was caused from the shorting electrical loads after damage to the insulation.



Power Feeder cables that have had their proper clamping removed at sometime in the past, causing rubbing and chaffing



Vibration is one of the factors affecting wire aging. Vibration is not at a single, constant level throughout the aircraft. It varies greatly as a function of location in the aircraft, and as such it affects the wiring running through those areas differently. Mixing wires of different types in the same bundle has been shown to be detrimental to wire life, because the harder coating on one wire can cut through the other when the wire bundle is subject to vibration.

Note: Wheel wells, engine compartments, and areas near the air-conditioning packs all have different vibration cycles. Vibration levels on airplanes can be found in 20-02-30 of the SWPM.

This APU main power feeder’s insulation was breached because of abrasion with consequent shorting of the conductor to ground.

A relatively unknown type of abrasion is under plastic tie-wraps. Because of excessive force used in tightening the wraps, the plastic material can dig into the insulation and abrade the material over a long period of time. Correct tightening procedures using Panduit guns set to the correct torque helps overcome this problem.



This example show how wires crossing over each other will literally saw into each other until the insulation is breached. Arcing and other damage will occur as this happens. This is a conduit that has a bend at the yellow circle. The conduit has been distorted by unknown means; hand or foot at one time in the airplanes life. Any damage to conduit means that the wires will probably have been damaged inside and therefore both conduit and wire will have to be replaced, repaired and inspected because of the danger of abrasion. .

These are the power feeders that came out of the damaged conduit. Notice that they had completely rubbed through right at the pressure point which was created by the kink in the conduit



This bundle of wire was breached in several locations. All of the abrasion was contained within the wire bundle. However, the bundles had not been properly tied in a high-vibration area As a result there were several openings to the conductors worn through

Heat Damage The next example of insulation damage is heat damage. There are specific wires that are designed to survive in high-heat environments. The following pictures represent a few wires that were not designed to withstand that heat. Temperature is a factor affecting the aging rate of wire insulation. Elevated temperatures increase the degradation rate, as do large, repeated temperature variations (thermal cycles). Wiring insulation is subjected to heat generated by the wire itself, as well as the heat from the surrounding equipment



These wires were all exposed to heat, such as over current, touching a bleed air return, or not being clamped away from heat sources in engine or APU areas. The first indication of heat damage is discoloration of the insulation, sleeve, lug or shrinkable sleeve. When heat indication or damage is found, immediate action must be initiated to remove the heat source and repair the damage normally by replacement.





The common factor to all of these wires is that the conductor became exposed. Without insulation, the power in the wire can go directly to ground or arc to another wire. All of these problems can be avoided with due care to the necessity of helping the wire to survive.



Fluid Damage The key for surviving exposure to fluids is for the insulation to remain intact. The wires were designed to withstand extreme environments, but without their outer skin of insulation, this cannot be accomplished. Any event that causes the wire's protective coating to be compromised will induce damage if exposed hen to fluid contamination. The following photos represent some wires that have been damaged, and the results in one case of that damage from being exposed to fluid after having the outer skin affected in some fashion

These cracks in the wire insulation are from bending, fluid attack and compounded by old age. Notice the underlying insulation that has been changed by the fluid into a slimy substance who's dielectric strength has been compromised

These are three different views of the same wire. This wire has had its outer cover breached, (red arrow) allowing lavatory fluid (blue water) that had leaked to contaminate and break down the insu1ator.A~ the wire was handled the insulation fell off the inner insulating material eventually exposing the conductor. Even a wire which appears to have only minor damage can be completely ineffective to protecting the wire.



Nicks, Scrapes, and Maintenance Damage One of the most damaging events to a wire is to have its covering compromised. This can happen by any of several methods, to include being nicked, scraped, or being the recipient of poor or ill-advised maintenance practices. The following photos represent just a few examples of these types of damage

These wires had been pinched under the tongue of the clamp. The conductors had both been exposed to a shorted-out situation when the insulation was compromised. These wires had been dragged across a sharp edge when being moved to facilitate repair to another component. Again, the conductor was exposed after the insulation was compromised.

This is an example of a typical breach or in older aircraft wiring. A deep hot stamp was the culprit on this one. A breech such as this will allow a direct path for any fluid contamination to enter and compromise the wire



Carbon Arcing Carbon arcing is a very dangerous phenomenon that can happen with aircraft wiring. All organically based insulation materials have a carbon base. All plastics are organically based, as they come from derivatives of oil. As stated earlier, wires that are in the aircraft that you may encounter must be suitable for their task. This is however, not necessarily the case if the insulation on two co-located wires has been compromised (Figure 3.15). When this happens, if the conditions are just right, the electricity in one wire can arc over to the next wire (Figure 3.16). When this happens, the organically based insulation can break down to its carbon base. Carbon is an excellent conductor of electricity. These arcs, even though they may last for merely thousandths of a second can create such intense heat as to cause this break down to carbon Every time that this particular wire now arcs in the same place can cause the insulation converted to carbon to grow. Because carbon is an excellent conductor of electricity, this will allow the arc to begin to travel the wire, (Figure 3.18) converting more and more insulation to carbon effectively turning the insulator into a conductor over time. The best defence against carbon arcing is strict adherence to the housekeeping and inspection requirements, as well as the proper repair techniques of the wire in the airplane.



Electrical Bonding and Grounds In this section will learn the basic electrical definitions, proper inspection standards, primary bonding, secondary bonding, and information concerning lightning strikes and HIRF protection. Introduction Definitions

Inspection Standards

Primary Bonding (Structure)

Secondary Bonding (System Grounding)

Cleaning and Corrosion Control

Lightning Strikes

High Intensity Radiated Field (HIRF)

Shielding



Introduction Airplanes in flight are susceptible to various environmental hazards including lightning and high intensity radiated fields (HIRF). Both these conditions can impose sudden, serious damage to critical and essential airplane systems such as electronic engine controls, high lift devices and primary flight controls, and can affect safety of flight. Protection from this condition is built into Boeing airplanes through shielded enclosures and shielded wiring which are grounded to airplane structure.

Term Definition Basic Structure The major, electrically integral, metallic part of an airplane Case Ground A current return path through the equipment mounting surface

Critical Ground

An important current return path; the voltage drop (resistance) from the wire terminal to the structure must be measured after the assembly of each wire terminal to a ground

Current-Return Ground

A current path or connection that is established between the ground side of the circuit of an electrical or electronic device and the basic structure; made with a designated ground lead or wire on the non-case grounded equipment with either a direct case to the structure ground or a jumper on the Case Grounded equipment

Designated Bond

An important bond; the maximum permitted resistance and the other major conditions are directly specified; are designed to permit the operation of a circuit-protective device, reduce any fire or explosion hazards, avoid electric shocks to personnel, minimize radio interference; examples include bonds for lightning protection, static bleed-off, and case bonds for electrical and electronic equipment in flammable Leakage zones

Dual Ground A type of connection that has two physical paths of the current return to structure

Dual Terminated An alternative term for Dual Ground Electrical Bond A stable connection between two objects that has the result of electrical

conductivity between those objects

Explosion Hazard Area

A work area, or the area of an airplane or any other manufactured product that is identified by the responsible organization as a hazard because of the combustible or explosive substances in the area



Inspection Standards There are numerous inspection paragraphs for electrical bonding and grounds. All are found in Chapter 20-20-00, Paragraph 6 and include the maximum permitted resistance of electrical bonds, such as:

Ground stud bonds Faying surface bonds Conductive finishes and panels Connector shell bonds Static discharger bases mounted on composite surfaces Hydraulic fitting bonds inside a fuel tank Bulkhead fitting bonds Clamp and conduit or tube bonds Adjacent surfaces of fiberglass Ground module bonds S280W5550( ) & YHLZG-( )

Technicians must always refer to the appropriate section of the SWPM before performing the inspection. See this Figure

General lnspection Procedures for Electrical Bonds.



Typical Bonding Test Graphic.

Inspection will always include measurement of resistance using a Bond Resistance Meter; a very accurate resistance measuring meter. Approved meters by Biddle, BCD and Avtorn, are found in 20-20-00 and must be used as follows:

Meter is calibrated with an accuracy of +-5% of the range specified by the manufacturer of the equipment Value of the resistance is not less than 10% of the full range of the meter The meter has a four probe design with separate current and potential probes

Note: A satisfactory alternative to measure resistance that are greater than 1 ohm are an Ohmmeter or Multimeter.



Primary Bonding (Structure) Unless it is specified differently, the resistance values given in Chapter 20-20-00. of the SWPM refer to the overall resistance as it is measured across the bond from the object to the' basic structure. See this Figure

Structural Bonding Resistance.

Secondary Bonding (Systems Grounding) A current return ground must be tested if it has been changed, added to, or temporarily disconnected. The maximum resistance between a ground stud and the structure in which the ground stud is installed. See Figure If the bonding test is not within limits then the bonding area will have to be cleaned in accordance with SWPM Ch 20- 20-00.

Ground Stud Resistance



Cleaning and Corrosion Control If corrosion is found under a bonding point then that corrosion must be removed and a new conversion coating like Alodine (for aluminium) applied. All procedures must be followed in the applicable section in the SWPM unless Boeing engineering authority has been obtained.

Rotary Corrosion Removal Tools

The rotary bonding brush is used to remove Alodine, paint, or light anodization from materials, including corrosion. The disc mandrel is used to remove the above including anodize coatings, skydrol resistant finishes and similar hard finishes. Note: Bonding Brush tools are colour

coded. No colour for aluminium, blue for stainless steel and red for composite materials.

Note: For any material, do not use a

bonding brush or disc that has been used on another type of material.

Note: Make sure to keep the loss of

material and the damage to the surface to the minimum.

When replacing parts of a bonded joint, ensure that the correct parts are fitted in accordance with the SWPM.



Lightning Strikes A lightning strike can cause direct physical damage to an airplane and, through circulating current coupling, can indirectly affect critical and essential systems. It occurs only about once every 3,000 hours (about once a year) on a commercial airplane. This rate is frequent enough for a lightning strike to be considered almost inevitable. Lightning produces a current in the airplane skin, generating voltages across joints in the skin and structure, These currents couple or connect to internal airplane wiring by way of the electrical and magnetic fields that are generated by current flow. Lightning strike energy can be transferred or coupled through non-metallic skin panels to electrical wiring and equipment. It can also have a sufficient magnitude to cause a system failure if it is not attenuated. As a result of extensive studies, the aircraft have lightning protection systems which include transient suppression filters and metallic shields over the wire bundles. Susceptible areas to lightning strikes are identified by the red area in the diagram shown in figure10.6 below.

Lightning Strike Areas.

Lightning strikes vary in intensity and duration. When designing airplanes. Boeing assumes that all lightning strikes are of a high intensity and duration and therefore a certain amount of current must be shunted to ground to minimize the amount that is indirectly coupled to internal wires. These electromagnetic fields are created at the airplane surface, inducing voltages inside the airplane that can cause damage to electrical equipment or cause it to malfunction indirectly. The resulting effects, known as lightning indirect effects, range from tripped circuit breakers to computer malfunction to physical damage of input or output circuits in electronic equipment.



High Intensity Radiated Field (HIRF) HlRF is generated by lightning strikes and various radio frequency (RF) emissions such as high power radio and television signals and radar. It can also affect the proper functioning of critical and essential systems. Low-intensity RF can originate from personnel electronic devices such a laptop computers and cell phones used by passengers in flight. These low-intensity devices can also affect critical and essential systems. Electromagnetic interference from these devices is suspected as the cause of many unexplained flight control upsets. The recommended approach to mitigating the harmful effects is to shield and ground the electronic equipment and the interconnecting wiring. As a result, electrical currents generated by lightning or HlRF then circulate through the equipment enclosure to ground without affecting internal circuitry. This enclosure practice extends to interconnecting wiring through the use of cable shielding; that is, is the enclosure that is grounded. Other damage mitigation considerations include the location of the equipment and wiring, and use of good grounding practices. Shielding Cable shielding is a key component in protecting critical and essential airplane systems from the damaging effects of lightning strikes, HIRF, and other potentially harmful environmental hazards. The advent of fly-by-wire airplanes such as the Boeing 777 has further increased the importance of this protection.

Class 3 Shielded Cable with Solder Sleeve



No single point on an airplane can be considered "ground," so the entire airplane structure is typically used as a ground. If a shield is grounded at both ends of a cable, circulating currents go into the structure and return through the shield ground path at the other end, creating a loop. The circulating loop current cancels the magnetic field that produces common mode voltages. This concept is directly counter to the reason for establishing a single-point ground and calls for shields to be grounded at both ends. However, installing dual shielded cable with the inner shield grounded at one end and the outer shield grounded at both ends eliminated hum while maintaining lightning protection. If circulating currents mitigate the effects of electromagnetic fields, keeping the shielding resistance low will maximize the protection. Testing for this low resistance is a direct measure of the protection A new shielded cable properly installed will exhibit a certain amount of resistance in the shield circuit. By monitoring this resistance, maintenance personnel can determine the ability of the shield to protect internal wiring. Measuring shield path resistance directly indicates what voltage level will be reached and allows testing limits to be established for determining when corrective action must be taken. Any increase on resistance indicates that a problem is occurring in the circuit, such as corrosion at a junction, connector, or loose hardware. When the resistance reaches a certain level, maintenance personnel must take corrective action, usually by cleaning the affected junctions, securing loose connections, or replacing the cable. Note: Further information on testing shielding can be found in Aero magazine Vol.10, Loop Resistance Tester. The FAA released Flight Standards Information Bulletin for Airworthiness #97-16A on the subject of Lightning HlRF protection maintenance. The bulletin contained guidelines for FAA inspectors to use for ensuring that in-service airplanes maintain continued airworthiness against lightning and HIRF hazards. Each operator was request to provide a lightning HlRF protection maintenance program to the appropriate FAA district office for review and approval This activity was required for all models including earlier airplanes with mainly analog electrical/electronic controls and displays although not all aspects of the bulletin would apply to the earlier airplanes

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