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
