Untitled Flashcards Set
Aviation Maintenance
Practices I
Final
EASA Module 07A Maintenance Practices 1
Learning objectives:
After the end of the week, the students must be able to:
➢ Understand the fundamental components, structure, and function of the EWIS.
➢ Learned various methods and techniques for proper wire termination. ➢ Learned about the installation, maintenance, and safety considerations associated with junction boxes.
➢ Identify different types of AN/MS connectors and their respective uses. ➢ For this PPT we will be focusing on the (Electrical Wiring Interconnect System (EWIS) – Wire Termination – Junction boxes – AN/MS connectors)
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Electrical Wiring
Interconnect System (EWIS) EASA Module 07A Maintenance Practices 3
Electrical Wiring Interconnect System ➢Electrical wiring interconnect system or EWIS encompasses a wide
array of components and devices designed for transmitting electrical energy within aircraft.
➢EWIS includes the following:
➢Wires and Cables
➢Bus Bars
➢Termination Points EASA Module 07A Maintenance Practices 4
Electrical Wiring Interconnect System ➢EWIS includes the following:
➢Connectors
➢Connector Accessories
➢Grounding and Bonding Devices ➢Electrical Splices
➢Protective Materials
➢Shields or Braids
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Electrical Wiring Interconnect System ➢EWIS includes the following:
➢Clamps and Routing Devices
➢Cable Tie Devices
➢Identification Labels
➢Pressure Seals
➢EWIS Components within Equipment
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Insulation
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Insulation
➢Insulation in electrical systems serves as a protective barrier, ensuring the safety and efficiency of electrical conductors.
➢There are two fundamental properties that define insulation materials: Insulation resistance and dielectric strength.
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Insulation
➢Insulation Resistance – Insulation resistance refers to the ability of the insulation material to prevent current leakage through and over its surface.
➢Dielectric Strength – Dielectric strength signifies the capability of the insulator to endure potential differences or voltage without breaking down.
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Selection of conductor insulation
➢The selection of conductor insulation material depends on various factors like the environment in which they will be used. ➢Characteristics such as abrasion resistance, arc resistance,
corrosion resistance, cut-through strength, flame resistance, mechanical strength, smoke emission, fluid resistance, and heat distortion need to be considered.
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Selection of conductor insulation
➢Older aircraft may have used materials like PVC/Nylon, but newer aircraft designs primarily utilize more advanced materials such as Tefzel®, Teflon®/Kapton®/Teflon®, and PTFE/Polyimide/PTFE due to their superior properties.
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Bonding and Grounding EASA Module 07A Maintenance Practices 12
Grounding
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Grounding
➢Grounding involves electrically connecting conductive objects to a common point or conductive return path. ➢Proper grounding is essential for the safe completion of circuits, especially during normal and fault conditions.
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Grounding
➢Multiple return currents – different types of return currents (e.g., from DC and AC sources) should not be interconnected or connected to the same ground point.
➢Safety concerns – connections within flammable vapor areas need to avoid arcing, sparking, or overheating under various current flow or mechanical failure conditions, including induced lightning strikes EASA Module 07A Maintenance Practices 15
Bonding
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Bonding
➢Bonding refers to the process of electrically connecting two or more conductive objects that are not sufficiently connected otherwise.
➢This process ensures proper functionality and safety within the aircraft’s electrical systems.
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Bonding
➢The following key aspects and requirements related to bonding in aviation:
➢Equipment bonding – electronic and electrical equipment in aircraft require low-impedance paths to the aircraft structure.
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Bonding
➢The following key aspects and requirements related to bonding in aviation:
➢Metallic surface bonding – all conductive objects outside the aircraft (exterior airframe) must be electrically connected to the airframe using mechanical joints, conductive hinges, or bond straps.
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Bonding
➢The following key aspects and requirements related to bonding in aviation:
➢Static bonds – isolated conducting parts inside or outside the aircraft with a size over 3 square inches and a linear dimension beyond 3 inches, exposed to electrostatic charging due to weather conditions, should have a secure electrical
connection to the aircraft structure
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Testing of Bonds and Grounds
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Testing of Bonds and Grounds
➢After making connections, the resistance of all bond and ground connections should be tested before finishing. ➢The resistance of each connection should not exceed 0.003 ohm. Accurate measurement requires a high-quality test instrument.
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Bonding Jumper
Installation
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Bonding Jumper Installation
➢ Bonding jumpers should be short and installed in a way that keeps resistance per connection within 0.003 ohm. They should not interfere with the operation of moving aircraft parts or get damaged due to normal movement.
➢ To ensure low-resistance connections, non-conductive finishes on attachment surfaces should be removed, and wiring should not be directly grounded to magnesium parts.
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Bonding Jumper Installation
➢Corrosion Protection and Prevention – corrosion is a common cause of bonding and grounding failures. Post finishing completed connections with a suitable coating helps protect against corrosion.
➢Choosing appropriate jumper materials, such as aluminum alloys or copper, helps prevent corrosion.
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Bonding Jumper Installation
➢Ground Return Connection – Bonding jumpers handling substantial ground return current should be adequately rated to produce negligible voltage drop.
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Wire Termination
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Wire Termination
➢Wire termination refers to the process of preparing the ends of electrical wires for connection to terminals, connectors, splices, or other devices.
➢Proper wire termination involves stripping the insulation to expose the conductive part of the wire and then attaching terminals or connectors securely to facilitate electrical connections.EASA Module 07A Maintenance Practices 30
Stripping Wire
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Stripping Wire
➢Stripping tools should be used carefully to avoid nicking or damaging the wire strand.
➢After stripping, check the wire for damage.
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Stripping Wire
➢Ensure that the insulation is cleanly cut without frayed edges and that there’s no insulation left on the stripped area.
➢When removing insulation longer than ¾ inch with hand-plier strippers, it’s easier to do so in multiple operations.
➢Restore the natural lay and tightness of copper strands by hand or with pliers or needed.
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Wire Stripping with Hand Stripper ➢Insertion – Place the wire in the correct cutting slot for its size
➢Closure – Close the handles as far as they go
➢Release – Allow the wire holder to return to the open position
➢Remove – Take out the stripped wire
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Wire Terminals
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Wire terminals
➢Terminals are connected to wire ends for easier connections to terminal strips or equipment.
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Wire terminals
➢Factors to consider include;
➢Current rating,
➢Wire size,
➢Insulation diameter, ➢Compatibility of conductor material,
➢Stud size,
➢Insulation material,
➢Environmental application, ➢And the choice between solder or solderless connections.
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Terminal Strips
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Terminal Strips
➢Terminal strips are used to join wires, and those with barriers can prevent contact between adjacent terminals. EASA Module 07A Maintenance Practices 39
Terminal Lugs
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Terminal Lugs
➢Terminal lugs connect wiring to terminal block studs or equipment terminal studs.
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Copper and Aluminum Wire terminals
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Copper and Aluminum Wire terminals ➢Copper wire terminals – conforming to MIL-T-7928, can be used in solderless crip-style connections.
➢Aluminum wire terminals – they should be crimped to aluminum wire and should be position between flat washers when terminated on studs.
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Pre-insulated Splices EASA Module 07A Maintenance Practices 44
Pre-insulated Splices
➢ Installation of pre-insulated terminal lugs and spices requires a high quality crimping tool with size positioners for wires.
➢ Correct crimp depth – if the crimp is too deep, it might damage individual wire strands. If it’s not deep enough, it may not securely hold the wires or could lead to resistance due to corrosion buildup.
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Crimping tools
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Crimping tools
➢Various tools, from handheld to hydraulic, are available for crimping terminal lugs.
➢They ensure proper force application to create a secure connection between the wire and terminal while also securing the insulation support.
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Emergency Splicing Repairs
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Emergency Splicing Repairs
➢Temporary solution – broken copper wires can be temporarily repaired using crimped splices, cutting off tongues from terminal lugs, or soldering and potting broken strands.
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Inspection and Testing of Crimped Joints
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Inspection and Testing of Crimped Joints
➢Properly crimped joints should exhibit strength and stability when subjected to tension, ensuring they don’t slip or move.
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Junction Boxes
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Junction Boxes
➢Junction boxes serve as central points for organizing and distributing circuits to relevant harnesses connected to equipment. They may also house miscellaneous components such as relays and diodes.
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AN/MS CONNECTORS EASA Module 07A Maintenance Practices 56
➢Connectors (plugs and receptacles) facilitate maintenance when frequent disconnection is required.
➢The connector types that use crimped contacts are generally used on aircraft.
➢Some of the more common types are the round cannon type, the rectangular, and the module blocks.
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Types of Connectors
• Aircraft connectors are essential for reliable and safe electrical connections in demanding environments.
The most common types are:
1. Circular Connectors
2. Rectangular Connectors
3. Coaxial Connectors
4. Fiber Optic Connectors
5. Splice and Terminal Block Connectors
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Circular Connectors
• Round connectors with robust metal housings.
• It is commonly used in; power supply, signals, and avionics systems.
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Rectangular Connectors
• Compact connectors with high pin density.
• Avionics modules and systems with multiple circuits. EASA Module 07A Maintenance Practices 61
Coaxial Connectors
• Connectors for high-frequency signals
• Commonly used in; Communication systems, radar, and navigation
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Fiber Optic Connectors
• Connectors for light-based data transmission. • Advanced avionics, high-speed communication systems.
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Splice and Terminal Block Connectors
• Connectors for joining or terminating wires.
• Electrical repairs, circuit junctions. EASA Module 07A Maintenance Practices 64
Voltage and Current Rating EASA Module 07A Maintenance Practices 65
Voltage and Current Rating
➢Voltage Rating
-The maximum voltage a connector can operate at without insulation breakdown or arcing.
➢Current Rating
-The maximum current a connector can handle without overheating or causing damage.
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SPARE CONTACT FOR FUTURE WIRING EASA Module 07A Maintenance Practices 67
SPARE CONTACT FOR FUTURE WIRING
➢Spare contacts are included in connectors for future wiring needs.
➢A good practice is to provide two spares on connectors with 25 or fewer contacts; 4 spares on connectors with 26 to 100 contacts; and 6 spares on connectors with more than 100 contacts.
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WIRE INSTALLATION INTO THE CONNECTOR EASA Module 07A Maintenance Practices 69
WIRE INSTALLATION INTO THE CONNECTOR
➢In aircraft systems, wires in redundant systems should use separate connectors for safety. System operation and failure warning wiring should be kept apart to reduce risks.
• For wire installation:
1.Use a color-coded plastic tool (Red for size 20, Blue for size 16, Yellow for sizes 12 and 22).
2.Insert the wire and contact into the tool, squeeze to secure the wire, then pull it through until it seats.
3.Insert the contact into the connector and push until it clicks into place.
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• For wire removal:
1.Position the tool, squeeze the wire, and pull the connector away.
2.Slide the tool into the connector to unlock the contact, then pull the tool and wire assembly out.
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ADJACENT LOCATION
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ADJACENT LOCATION
• Adjacent connectors should be designed to prevent incorrect mating, using different sizes, keying, or coupling.
• If not possible, wires should be routed to avoid incorrect connections. Avoid relying on markings or color stripes.
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SEALING
• Connectors must prevent moisture entry with proper seals and grommet compatibility.
• Only one wire per crimp contact is recommended. Heat shrink tubing or potting may be used but only as a last resort.
• Spare contacts should be sealed with plastic plugs. EASA Module 07A Maintenance Practices 74
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DRAINAGE
• It is Installed to connectors to allow moisture to drain away. Mount vertical connectors with receptacles facing down to reduce moisture buildup.
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END OF PRESENTATION EASA Module 07A Maintenance Practices 77