7.7 EWIS Flashcards
What do wiring checks normally include?
- visual inspection
- continuity testing
- insulation resistance testing
- bonding testing
What is continuity?
Condition if being unbroken or uninterrupted
When is continuity testing carried out?
After bonding but before insulation test
What does a multimeter have to be set to test for continuity?
- set to the ohms range in the correct range
What two pieces of information does a continuity test give you?
- there’s an electrical link between two or more designated points within a circuit
- the resistance of that link is within a specified value
Should power be on or off during a continuity test?
NEVER apply power to a circuit when using continuity test equipment
When can the airframe of an aircraft be used as a return path for a continuity tester?
If it’s a metal fuselage
What are ohmmeters used for?
- to measure resistance of a circuit component or a complete circuit
- to measure the integrity of a connector contact at a disconnect
- the serviceability of circuit components
What are the advantages of an analogue multimeter?
- does not need a battery
- cheaper than a digital one
- easier to see slight fluctuations in voltage and current as the needle moves gently
- More suitable for adjusting tuning circuits or peaking tuneable responses
- less prone to temp arrors
What are the disadvantages of an analogue multimeter?
- tends to be less accurate bc of user error
- larger and bulkier
- most analogue meters only read ohms, volts and Amps. (AVO)
What do insulation testers identify?
- current leakage
- faulty or damaged insulation
Can lead to arc faults, blown circuits and risk of electrical shock or fire
How do insulation testers identify current leakage or faulty isolation?
Use high voltage and low current DC charge to measure the resistance within wires and motor windings
What is the general purpose of insulators in aircraft?
To separate conductors from each other and the air frame
What kind of insulation failure can trip the circuit breaker?
When the insulation is protecting the conductor from touching the airframe and causing a short circuit
When are insulation resistance tests necessary?
- when new circuits are installed
- existing circuits are disturbed
- evidence requires installation to be checked
What tests are normally carried out before insulation resistance tests?
Visual checks, bonding and continuity tests
What does a typical insulation testing device consist of?
- a pointer
- A hand driven generator or internal HV source
- connecting leads
- varying voltage outputs chosen by a selector switch on the meter
What should the voltage be when using an insulation resistance tester?
Minimum 3 times the normal working voltage
How does a hand cranked insulation tester work?
- Two coils produce two fields
- this provides a deflection depending on the resistance encountered
What does it mean if components are bonded?
- all components have the same potential energy
- there are no parallel paths open to current flow
What ensures the safe path for current flow or return path for the system to complete the circuit?
Bonding
How does bonding give electrostatic protection?
- protects against build up of static charges, lightening strike follows the path of least resistance through well bonded leads on to protection devices
What does grounding do that bonding doesn’t?
- Eliminates the potential difference between components and the ground
- provides a conductive path to the earth for static charge so sparks aren’t created
How is grounding done?
- electrical connection of a conducting component to the primary structure
What is the primary structure used for grounding?
- Primary structure is the main frame, fuselage or wing structure of the aircraft
- Current Return Network for composite planes
Do AC and DC systems share grounding points?
They have different grounding points in different locations to prevent parallel return paths
What are the three main types of bonding?
- Equipment bonding
- Metallic surface bonding
- Static bonds
What is required for electronic equipment to provide radio frequency return circuits and to facilitate a reduction in EMI?
Low impedance paths to the aircraft structure
What condition must all conducting objects on the exterior frame meet?
Must be connected to the airframe through mechanical joints, conductive hinges or bond straps capable of conducting static charges and lightening strikes
Why do antenna elements not have to be electrically connected to the airframe?
Their function requires them to be electrically isolated
What parts must be statically bonded?
- all isolated conducting parts inside and outside the aircraft with an area greater than 3 in squared and a linear dimension over 3 inches
What should the resistance be of clean and dry isolated conducting parts inside and outside the aircraft that have it be statically bonded?
Less than 1 ohm
What should be inspected for when doing bonding inspections?
- arcing
- conduit bond
- corrosion
- freedom of movement
What can arcing be prevented by?
Bonding or by insulation if bonding isn’t necessary
If electrical arcing is found, what should you check for?
Intermittent electrical contact between conducting surfaces that can become a part of a ground plane or a current path
How is the metallic conduit in a conduit bond bonded to the aircraft structure?
- Metallic conduit must be bonded to the aircraft structure at each terminating and breakpoint
How should the conduit bonding strap be connected in a conduit bond?
The conduit bonding strap must be ahead of the piece of equipment that’s connected to the cable wire inside the conduit
What type of screws can’t be used for bonding purposes?
Self tapping screws
Can bonds be attached through other bonded parts to the aircraft?
No, must be bonded directly to the aircraft
What resistance must the bonds between exposed conducting frames, or parts of electronic equipment, have to the structure?
- Low resistance bond of fewer than 2.5 mΩ
- If it has a ground terminal or pin that is internally connected to exposed parts a ground wire connection to the terminals can be used.
What type of joint is a bond.
An electrically conductive joint
How can you establish if an electrical ground has been established between two points?
By carrying out a bond test
What is the purpose of grounding and earth points?
- where the AC and DC systems find their respective return paths
- Where cable screening is connected to the ground
What is an earth point?
Where electrical earth and neutral terminations are made
Where are earth points usually located (relative to connector groups)?
Adjacent to or included in the connector groups
Where can single earth and grounding points be found?
Around the aircraft
Why are AC neutral wires and DC earth wires not connected to the same earth post?
To prevent feeds from the AC neutral through the DC system to earth if the wires have a weak connection at the earth post
How are earth posts or terminal blocks tested to make sure they’re electrically bonded to the aircraft structure?
- First part: bonding test
- Secind part: millivolt drop test
What is the corrosion tag or plate incorporated in each earth post assembly for?
To prevent electrolytic action between the base of the assembly and the airframe structure
How are Burndy type terminal blocks mounted on the plane?
Mounted directly on to the airframe
Why does the YHLZG family of terminal blocks not require circuits to be separated
It has more than one point of connection with the airframe structure
What do hand held crimps use to crimp?
- hand power
- certi ratchet mechanism
When are hydraulic crimping machines used on the aircraft?
- where generator feeder cables or power terminals require crimping and. A handheld one can’t handle the AWG
What are the three ways to strip the insulation from wire?
- using a single blade or scalpel (not recommended)
- double blade
- thermal
When both the conductor and insulation are crimped, what contributes to the overall crimp and termination strength?
- depth of the crimp
- length of the bared conductor
What is critical when only crimping the conductor?
- strip length
- Diameter of the stripped wire portion
What is critical when only crimping the conductor?
- strip length
- Diameter of the stripped wire portion
What supplies the hand held hydraulic crimp tool with pressure?
The pumping action
What is a crimped connection?
Where a cable conductor is secured by compression to a termination so that the metals of both are held together in close contact
What is crimping?
Applying pressure across a contact connection where wire is inserted in to the barrel of a contact
The applied pressure causes a cold flow of contact metal in and around the conductor
Which creates a strong joint
What does the strength of a crimping joint depend on?
The depth of the crimp
What do all crimping tools have to stop the tool from opening once the crimp sequence has started?
A self locking ratchet
When can a crimping tools self locking ratchet be disassembled?
Never
Where can the correct tools for crimping be found in Airbus and Boeing?
- Boeing Standard Wiring Practices Manual (SWPM)
- Airbus Electrics Standard Practices Manual
How many stages is cut and pull action of the double blade cable strippers?
- Five independent stages
- coordinated using mechanical handle interlocks
What do hand crimping tools have to accommodate the wide variety of contacts that can be crimped?
Interchangeable turret heads or positions
How can crimping tools be checked for proper calibration?
- select waiter selector to position no.4 for 1-01 tool or no.8 for 2-01 tool
- fully close crimp handles and hold
- Insert the GO and NO GO tool
What is the engaging end of the contact?
The size of the AWG
What are the advantages of using crimps?
- good conductivity
- uniformity of operation
- corrosion proof
What are the most common methods for wire terminations?
- solderless
- crimped termination
What is the ideal shape for a crimp?
- round
- but in practice hexagonalmalso gives good results
What are the most common terminal lugs used?
- Manufactured by Aircraft Marine products
- Pre-insulated Diamond Grip type
How is an AMP crimping tool marked to assist with using the correct components for each wire guage?
- handles are colour coded red, blue or yellow for cross reference w the wire and the actual crimp
- the wire gauge is stamped on the plier jaws
AMP crimp tool:What makes sure of the bottoming of the dies jaws before they’re opened again?
Certi- crimp ratchet
AMP hand crimping tool: How much should the conductor strands protrude from the barrel?
1/32 inch
AMP hand crimping tool: What makes sure the terminal is in the correct position and the conductor strands are protruding ?
The locator
What are the insulation die heads three degrees of adjustment?
Loose no.3
Medium
tight no.1
What AWG is marked by yellow?
26- 22
One dot
What size range is the red tool handle tool?
22-16 one dot
What size range is the blue coloured tool handle for?
16-14
Two dots
What size wire is used w the yellow coloured crimping tool?
12-10
One dot
When can AMP in- line splices be used in the aircraft?
For temporary repairs in unpressurised areas
What type is sleeves do AMP PIDG terminal lugs and splices have?
Plastic or nylon insulating sleeves covering the shank or barrel
How much insulation should be stripped before crimping?
Barrel length (c) + 0.8mm
What should you check for after putting wire into the end of the splice?
- the end of the conductor can be seen in the inspection hole
- end of the conductor doesn’t overlap the wire stop
- insulation of the wire is not in the crimp barrel
- end of the wire insulation is max 0.13 inches from the end of the crimp barrel
What dies can be used for most coaxial and biaxial connectors and contacts?
Hexagonal crimp dies
What two things does the quality of a crimp depend on?
- it’s mechanical strength
- it’s electrical conductivity
What are the three different methods of checking and testing a crimped joint?
- visual inspection
- tensile test or pull test
- Volts drop test
What type of PIDG must be used on thin wall cable?
A restricted entry PIDG terminal must be used
Which is male and female out of pins and sockets?
- Pins are male contacts
- Sockets are female contacts
What are the two main parts of a connector?
A plug and a receptacle
What do plugs and receptacles consist of?
Contacts (pins and sockets)
If there are no contacts an environmental seal is preserved within the connector
How are environmental seals preserved within a connector?
Using fillers or blanking fillers
What type of design do receptacles have to prevent a shorting of contacts?
A scoop proof design
How are front release contacts removed from a connector?
- insert extracting tool into the connector from the front
- uses a plunger to push the pin or socket out the back of the connector
How can a contact be pulled out from a rear release connector?
- contact removal tool inserted into the contact cavity from the back or rear of the connector
- this releases the contact retention clip
- contact can be pulled out
Where are contacts inserted from for front and rear release?
Inserted through the rear of a connector
What is the size of a contact dependent on?
The current carrying capability of the wire it’s supporting
What tool is used for removal and insertion of AWG 12,16 and 20?
AWG 12: yellow tool
AEG 16: a blue tool
AWG 20: red tool
What are rear release connectors identified with?
Blue band around the shell or blue line on the back of the shell
What is an advantage of rear release connectors?
The contacts are less susceptible to damage during removal as the tool does not shroud over the contact
Which end of the plastic contact tool is for insertion and removal?
Insertion: coloured side
Removal: white
How is an unwired contact removed?
Using an unwired contact removal tool
How do you insert a contact in to a terminal block?
- first insert by hand
- than use the approved insertion tool
What is the main difference between a wave guide and co- axial cables?
Waveguide operates at a higher frequency
Why is it important for the characteristic impedance if a cable to be matched correctly to the circuit?
If it is not matched correctly, reflected waves can return to the source
Why is fibre optic cable now used on the new generation aircraft?
It enable high speed data transfer
What frequencies are co axial cables used for?
Below 5000 MHz (5 GHz)
For what frequencies are waveguides used?
For frequencies above 5 GHz (5000 MHz)
What type of coaxial cables are not used on modern aircraft anymore?
Rigid coaxial cables
What material is used for the dielectric of flexible coaxial cables?
- foam or polyethylene
- most modern ones use foam
Why is polyethylene or foam used as the dielectric in flexible coaxial cables?
unaffected by such fluids as acids, alkalis, aviation fuel oil, hydraulic fluids, or seawater.
Coaxial cables: What is the advantage of using foam as a dielectric?
- weight saving
- allows you to fit cables with a smaller diameter which adds to the overall performance of the aircraft
When are cable losses the lowest when using foam and polyethylene cables?
At the lower radar frequencies
What are the four types of transmission line losses?
- copper
- dielectric
- radiation
- induction losses
Why are copper losses experienced by transmission cables.
- the resistance of the copper conductor causes some losses
- the skin effect: tendency for AC currents to flow near the surface of a conductor, higher conductivity at the surface
What causes dielectric losses in transmission cables?
- heating the dielectric material (insulation) between the conductors
- heating is caused by the disturbance of orbits of the electrons bc of potential differences between the conductors
- the movement of the electrons uses power from the RF input for the line
How can dielectric losses in transmission lines be reduced?
Through selecting materials whose atomic structure is readily distorted so that lots of power isn’t used to disturb the electrons
What is radiation loss in transmission lines?
Electromagnetic energy escaping the cable and radiating in to the environment
What causes radiation losses in transmission cables?
- imperfections in the cables insulation
- discontinuities in the outer conductor
What can radiation losses in transmission lines cause?
- signal attenuation (weakness)
- interference
How can radiation losses be minimised in transmission lines?
- proper shielding
- using materials that reduce electromagnetic leakage
What causes induction losses in coaxial cables?
- a magnetic field is created around the conductor when current flows through the inner conductor
- the magnetic fields induces eddy currents whose magnetic fields oppose the inner conductors original magnetic field
- the interaction of the opposing magnetic fields causes an energy loss through resistive heating of the cables material
(Main bit is loses energy through the resistive heating of the cables material bc of opposing magnetic fields)
How are induction losses mitigated in coaxial cables?
- shielding between the inner and outer conductors to maintain the magnetic fields and reduce the induction of eddy currents in the outer conductor
What does VSWR stand for?
Voltage Standing Wave Ratio
What installations are coaxial cables most commonly used in?
- radio
- antennae connection
- capacitance fuel type quantity indicating systems for interconnection of tank units and amplifiers
What can a bad connection, poor crimp or stray conductor strand cause in coaxial cables?
- reflected waves
- system damage
- localised cable hot spots
What are the parts of a coaxial cable? (Inner to outer part of the structure)
Inner multi strand main conductor
Dielectric (insulation)
Braided shield outer conductor
Outer weatherproof wrapper (insulation)
Coaxial cables: what is the inner most conductor made from?
- solid or stranded copper wire type
- plain, tinned, silver, plated or even gold plated
Coaxial cables: what is the dielectric insulation made from?
Polyethene or Teflon
What type of coaxial cable has to be used if direct replacement is necessary?
Stranded coaxial cables not outdated coaxial cables with solid centre conductors
Why can’t cable ties be used with coaxial cables?
They can crush the dielectric and damage the cable
What is the only acceptable way to pull a coaxial cable?
In a straight line
How can you further minimise radio frequency interference of a coaxial cable.
Make cable runs as direct and short as possible
Coaxial cables: where should the braided outer conductor be grounded?
- at one end, or both ends depending on the installation
What’s the minimum bend radius of a coaxial cable?
Six times the diameter of the cable
What re the intervals that coaxial sables must be supported at?
Min 61cm (24in) intervals
Coaxial cables: how are connectors chosen?
- based on whether the braiding is connected to the ground
- based on the system and environmental conditions
What type of connectors are used for coaxial cables?
Bayonet Nut Coupling (BNC)
Threaded nut coupling (TNC)
Coaxial cables: What are the main components to assemble connectors?
- connector body
- centre pin
- k- grip sleeve or grip sleeve
- ferrule
What crimp is crimped to the inner centre conductor and which to the outer conductor?
Inner centre conductor: crimped to the pin
Outer conductor: crimped to the grip or k grip sleeve
What crimping tools are used for coaxial connectors?
Open frame crimping tools
What are the five main steps to prepare a coaxial cable for crimping?
- remove outer jacket
- cut braid to the correct length
- cut dielectric
- cut inner conductor
What are coaxial cables is pecten for after installation?
- continuity for each of the two conductors
- insulation resistance checks
- TDR time domain Reflectometer testing
- impedance
- Open circuit and short circuit conditions
What are coaxial cables is pecten for after installation?
- continuity for each of the two conductors
- insulation resistance checks
- TDR time domain Reflectometer testing
- impedance
- Open circuit and short circuit conditions
What is a TDR?
- time domain Reflectometer
- electronic instrument that characterises and loacates faults on a transmission line incl coaxial cables
How are problems detected and displayed by a time domain Reflectometer?
- detects impedance along the cable
- sends an electrical pulse onto the cable segment under test, then displayed the echo of the pulse
what is a wire?
any type of single conductor surrounded by insulation
What is most aircraft wire made up of?
- stranded copper conductor
- small wire: 7 or 19 strands
- larger wire: 19 or more
what is the structure of flexible wire?
made of several small strands
what is wire made of when it must carry lots of current over large distances?
made of aluminium
What is a cable defined as?
a group of two or more conductors separately insulated and grouped together by an outer sleeve
What is a cables main disadvantage?
inabiliity to repair or replace a single wire
What are the two methods of applying cable insulation?
- wrapping
- extruding
These provide different “handling” techniques
what are airframe cables known as in the US?
Medium weight interconnect
what are interconnect BSI cables used for?
- Used in protected areas of wiring
- Not “pulled through” and other stressful exercises
What is the advantage of a BSI interconnect cable?
- Thinner
- Which saves weight, space and increases flexibility
What are BSI interconnect cables known as in the US?
- Hook up
- Light weight interconnect
what is equipment cable used for, and so what characteristics does it have?
- to be used within equipment
- very flexible and suitable for soldering
what can equipment cable also be used for, though not designed to be?
- use in protected areas of an airframe even though it isnt interconnect wiring
what is equipment cable called in the US?
Module cable
Why was thin wall cable developed?
Bc of the need to carry and burn less fuel
What has replaced Kapton ( a type of thin walled cable)?
EWIS/ arc tracking
How long does fire resistant cable have to last at a certain level of electrical insulation in the presence of fire?
five minutes
How long are fireproof cables required to operate at in a designated fire?
15 minutes
Generally how many cores can airframe and interconnect cables in a multicore have?
four cores
How are interconnect and airframe cores structured in a multicore?
Cores are twisted together
How much surface coverage does the screening (usually a braid) give to a multicore cable?
85% coverage
When the screening of a multicore cable is replaced, what must be done regarding the standard?
- Can be replaced w a higher standard but never a lower one
How are antennas connected to most radio receivers?
co axial cable (shielded cable)
What is the advantage of a twisted cable?
Two opposing magnetic fields cancel each other out and wont interfere with other systems
What does a data bus usually consist of?
A twisted pair of cables surrounded by electrical shielding and insulators
What systems do the power feeder cables supply frequency to?
VSFG or IDG
What is the structure of a generator cable?
- High diameter, low AWG
- Extremely high current carrying capacity
- Copper cables from the generators to the wing root or engine pylon
- Aluminium where they supply the distribution contactors
Why are generator cables changed from copper to aluminium?
- save weight
What is a disadavantage of the series code?
Not possible to know where a wire is connected without looking at the WDM (wire diagram manual)
How is the series code imprinted on to cables?
Hot stamping at regular intervals
(must undergo stringent insulation testing after)
What are the first four digits of a wire code?
Wire number prefix, shows which aircraft system the cable is connected to
Cross references to its associated ATA system number
What is the wire number? (after the first four digits)
- Max five digits
- Used to differentiate between wires, cables, or coaxial cables in a particular subsystem
What is the wire segment letter for?
- helps you differentiate between two wires if they have the same wire number
(in the case theyre both permanently connected such as in terminal block or spice)
What AWG are all wires unless specified?
20 AWG
When do wires not have to be supported at minimum every 61cm?
When theyre contained in troughs, ducts or conduits
What must be used as stand- offs to maintain clearance between wires and structures?
Only metal stand- offs
What is the minimum bend radius of a bundle?
five times its outside diameter
How must a loom that breaks out be supported?
No more than 2.5 cm on either side of the breakout
At what intervals does a wire need to be identified?
Not more than 38cm/ 15 inches
What is the minimum distance that splices should be at (unless authorised)?
Splices should occur at no less than 3 meter (10 ft) intervals
How should wiring or coaxial cables be identified when replacing them?
Identified at both equipment power source ends
What is the minimum bend radii of thermocouple wire?
20 times the diameter as its very delicate
What is lacing?
Process of securing a group or a bundle of wires together
What does a wire bundle consist of?
two or more wire groups that are tied or laced together
What should the spacing be between ties?
engine and pylon areas: max of two in 5.08cm
Other high vibration areas: spacing is 6-8 in
outside aircraft vibration zones: can be as much as 3ft apart
What type of lacing should be used on cables larger than 1 inch diameter?
Double cord lacing
What type of lacing is used on groups or bundles of 1 inch or less in diameter?
single or double cord lacing
What are ties made from?
- waxed cotton cord
- nylon cord
- fibreglass cord
- pressure sensitive vinyl electric tape wrapped 3x and ends heat sealed (if permitted)
What temperatures can tie down straps not be used at?
Where total temp exceeds 85c
Where on an aircraft can tie down straps not be used?
- In high vibration areas
- Outside the fuselage
- In wheel wells
- Where its exposed to ultraviolet light unless theyre resistant
How must wire be protected in wheel wells?
With sleeves or flexible tubing held at each end
What is the maximum diameter of a bundle in a conduit?
must not be more than 80% of the internal diameter of the conduit
When repairing an aircraft, where should power be supplied from?
the GPU
Where chafing can not be avoided, what can wrapping can be used?
Spirap
What is the main difference between DVI and a Detailed Inspection (DET)?
DET can include tactile assessment
What is a zonal inspection?
Comprising selected GVI and visual checks that are applied to each zone.
What must all power feeder cables splices comply to?
The Type Certificate or Supplementary Type Certificate holders published recommendations
If there arent any reccs, use environmental splices
For what types of damages do electrical items have to be replaced?
- discolouration
- cracks
- expansion of the sealing grommets
- supploer marks erased
- loss of label adhesion
- functional item numbers erased on the label or placard sleeves
What is EZAP and what was it designed for?
- Enhanced Zonal Analysis Procedure
- uses logic diagrams to identify effective maintenance tasks to minimise the accumulation of combustible materials
- to permit appropriate attention to be given to wiring installations
When rating a wire to see how often it should be inspected, what is taken in to consideration?
- Possibility of accidental damage
- Environmental factors
What are the possible tasks for non-ZIP programmes?
- GVI
- DET
What things are considered principal causes of wiring degradation and are used to help focus maintenance programmes?
- Vibration
- Moisture
- Maintenance
- Metal shavings
- Repairs
- Indirect damage
- Contamination
- Heat
- Ageing
What has to be done before putting acid solutions down lavatory systems?
- confirm it to be free of leaks to make sure
In what areas are EWIS components more prone to contamination?
When they’re adjacent to oil and hydraulic systems
Why must corrosion preventative compounds (CPC) not eneter wires or its components?
Dust and lint is more liekly to collect on a wire with CPC on it
What are the two types of contamiantion to EWIS components?
- Natural
- Accidental
What should not be used if there is accidental contamination without knowing the material that caused it?
Any solvent
What natural contamination can be cleaned with isopropyl alcohol?
- aircraft hydraulic fluid
- fuel and oil/ grease
- de-icing fluid
- anti corrosion material
- dust
What steps are taken when there is liquid contamination?
- Stop the contamination source.
- Make a sealed barrier, usually with cloth, to stop the liquid and prevent contamination of the adjacent areas.
- Remove the contamination with a cloth or a vacuum cleaner for liquids.
What steps are taken when there is powder, granular or dust contamination?
- Make sure that there are no draughts.
- Remove the contamination with a vacuum cleaner.
