ELH Flashcards
Types of crimps
Type 1 - Indent crimp
Type 2 - Form crimp
Wire labels - Identify what each of the below characters refer to:
3 P 9 B 18 N
(Uncle Eddie Never Stops Saying Gagi)
First character (3) - Unit number
Second character (P) - Equipment identification
Third character (9) - Wire number
Forth character (B) - Wire segment letter
Fifth character (18) - Wire size number
6th character (N) - Ground, phase, thermocouple letter
Identification code for the below:
S
R
T
Y
S - Radar
R - Radio
T - Special electronics
Y - Armament special equipment
Construct of a coaxial cable?
- Inner conductor
- Tubular insulating layer
- Tubular conducting shield
- Many coaxial cables also have an insulating outer sheath or jacket
Things keep in mind when looming cables?
- Comb them
- Secure them with cable clamps
- Bend radius
- Drip loops
Distances for sleeve marking?
Standard cables
Coaxial cables
All cables:
- 3 inches from each end
- Every 3 ft or 90cm
Coax cables:
- 3 inches from the end
- 15 inches from each other
- Only sleeves (NO STAMPING) but treat it like direct marking
Calibration and functional serviceability check on mega?
- Check calibration sticker
- Connect the 2 wires together, set to 50v and press test button
- Should read 0 resistance
How do we test coax using the mega?
- one probe on the outside
- one probe touching the centre
- If the dielectric is doing it job then it will show loads of resistance
How do we test twisted pair with mega?
- one probe on one wire
- one probe on the other wire
- If the resistance is high then the wires are not touching at all and this is good
Types of wires found in aircrafts?
- Unshielded multi-conductor cable
- Shielded single conductor cable
- Shielded multi-conductor cable
- Twisted pair cable
- Coaxial cable
Types of wire markings?
- Direct marking
- Sleeve marking
Colour coding of copper terminal lug installations?
Red - 22, 20, 18
Blue - 16, 14
Yellow - 12, 10
When inspecting terminal blocks, what should you look for?
- Grease, oil and foreign objects
- Securely mounted
- Wiring is securely attached
- Wiring connectors are correctly positioned
- Maximum of 4 terminal lugs / 3 terminal lugs and a bus bar
- If sizes of terminal lugs vary, ensure they are layered largest at the bottom to smallest at the top
- Tend to tighten
Definition for bonding?
Electrical connecting of 2 or more conducting objects not otherwise adequately connected
Definition of Grounding? and what does it assist to prevent?
- Primary structure or earth or ground point
- Prevent issues with static / lightning
- Avoid sparking - fuel vapours lay low so you don’t want to connect to the aircraft and then have the static travel down the earth lead and cause sparking
- Prevent electrical hazards
What is a bonding strap used for?
- Braided wire
- Anything that moves needs a bonding strap
What is Zinc chromate paint coating used for?
- Protect against corrosion
Components of a Milliohm meter?
- RX socket
- LCD display
- ZERO ADJUST Knob
- Power Switch and Range Selector Switch
- D-H Button
How to check calibration and serviceability of a milliohm meter?
- Check cal sticker
- Place the 2 leads together
- Place the dial on the “200m ohm” position
- Ensure 0.00 ohms is displayed
Methods used for discharging static electricity in an aircraft?
- Earthing lead
- Static discharge wicks
- Null field dischargers
Difference between static discharge wicks and null field discharges
(Both bonded on trailing edge of the control surface)
Static discharge wicks - used on older, slower aircrafts due to lower speeds and lesser static to be discharges
Null field dischargers - used in modern aircrafts due to higher speed / increased static charges
Why is insulation testing important?
- Insulation breakdown can result in interference in things like radio frequency (RF)
- Prevent short circuiting
What piece of testing equipment is used to test insulation with the following characteristics?
High voltage
High voltage - Megger ohmmeter (Typically 50, 250, 500, or 1000 V DC)
Components of a megger ohmmeter?
-LCD display
- Rotary selector switch
- Test button
- Lock button
What is the megger ohm meter used for?
Testing conductivity
High resistance - low conductivity GOOD
Low resistance - high conductivity BAD
What are the following crimp connections used for?
Form crimp
Indent crimp
Form crimp - Electrical wires are terminated with solderless terminal lugs to permit easy and efficient connections to and disconnection from terminal boards etc
(Hexagonal tool)
Indent crimp - Solderless splices join electrical wires to form permanent continuous runs
(Bullet)
What is used to test the serviceability of a crimping tool?
Go / No go gauge
Wire repair methods?
- Single conductor wire splicing and repairs
- Multi conductor wire splicing and repair
- Single and multi conductor shielded wire splicing and repair
- Broken wire contact removal
- Connector removal and installation
Restrictions for wire splicing?
- Refer to pubs
- Repairs requiring multiple splices, MUST be staggered
- Splices MUST NOT increase the size of the bundle enough to restrict it from being used in the designated place
- Splices are NOT to be used 12 inches from the termination
- Not to be used on firing / control circuits for OE
- No more than 1 splice in any wire segment between 2 connectors
Must not conduct splice repairs in which 2 systems?
- Ignition system looms and harnesses
- Fire warning system looms and harnesses
When are coax cables typically used?
To carry radio frequencies (RF) power from one point to another with a known rate of loss
When are solder sleeves used?
- Connect a cable shield to a ground lead
- Terminate a cable
- Repair or replace the cable shield
3 portable tools commonly used for heating / soldering?
- Infrared heating tool
- HT-920B compressed air/nitrogen heating tool
- Turbofan type heating tool
Characteristics of electrical plugs / connections?
- Typically round and self locking
- Used in places where they can be frequently removed / connected
- Blue band means that it is a rear release (the tool goes in the rear)
Distance for bare wire to be left while soldering?
1 - 2 cable diameters
What is the milli ohm meter used for testing?
Bonding testing
What is the mega ohm meter used for testing?
Testing conductivity
What is an acceptable solder
- Under 45 degrees is acceptable
- 1 - 2 wire
- Shiny
- Concave filled NOT CONVEX
Fabrication of an ignition harness? How is it fixed?
- Carries voltage
- Replace the whole cable
- DO NOT SPLICE
Where is SDS found?
Chemalert
What is important when you build up an earthing point?
Aluminium to aluminium
Terminal board identification?
- Cover has been removed
- Identified by a part number ie. TB-2
- The abbreviation TB stands for terminal board and 2 identified the specific terminal board number
Lightning protection?
- Careful shielding
- Bonding
- The application of surge suppression devices
- Methods to discharge static charge
What publication is referred to for the repair of a coax cable?
AAP 7045
What publication is referred to for the repair of fire warning system harnesses?
None, the cable needs to be replaced
Hardware found in aircrafts?
- Clamps
- Nuts
- Screws
- Washers
Why are terminal boards used?
Convenient means of connecting individual wires
What does the resistance across a bonding point need to be?
Less than 0.1
What is a loom?
Type of flexible, braided insulating material put over wire or a bunch of wires to protect it against physical damage caused by heat and abrasion
What is a harness?
A harness is a bundle of wires routing through an aircraft
Loom tying?
- Authorised flat pre-waxed cord
- Square knot is used (modified clove hitch)
