EWIS
EWIS
EWIS
The accidents of SR111 and TWA 800 focused the airline industrys attention
on electrical problems and vulnerabilities. Investigations found common
degrading factors in airplane electrical wiring systems. As a consequence more Investigations into wiring issues were carried out by industry, civil
aviation authorities and government agencies. The investigation of the aircraft
wiring revealed that there are several factors, together with time, that play a
role in wiring degradation.
EWIS - Module A
General Electrical Wiring Interconnection System Practices
EWIS - Module A
At the end of this module you will know or be able to demonstrate safe
handling of aeroplane electrical systems, line replaceable units (LRU), tooling,
troubleshooting procedures, and electrical measurement.
Safety is a concept of great importance in aircraft maintenance. And is
therefore handled with the utmost care. In the air and on the ground. The
Maintenance Mechanic will deal with many Safety Regulations during his
work. These regulations may apply to work in, or outside the aircraft, as well
as the work done in the workshop or hangar. It takes a lot of time and effort to
establish a safe working environment, but the aviation community cannot
Safety preqution
Maintenance mechanics are applicated to protection their eyes, face, ears and
mouth. Safety glasses greatly reduce the chances of eye damage when
milling, grinding or welding metals or when working with acid fluids. Remind
yourself that every person has only one pair of eyes. Motoring or running
aircraft engines produce a lot of noise, more than 90 dB, so there is a possible
danger of damaging the eardrums. Ear protection should always be worn
when working around aircraft. When there is a possible danger of damage to
your feet, wearing safety shoes is recommended. Lack of awareness and
carelessness are the biggest opponents of mechanics' safety. Make sure that
you always aware of possible safety hazards and take the appropriate steps
to minimize the risks involved!
- Energize system.
Please note!
When external power is used to energize electrical system, check that voltage
and frequency of external power supply are set within required limits.
- Perform operational test.
- Return switches and controls to normal shutdown position.
Now we will look at the various crimping tools used on commercial aircraft.
This is a crimping tool to be used for spare wire caps. Here we see a crimping tool
for Closed end splices. More often you will see these PIDG crimp tools. PIDG stands
for Pre-Insulated Diamond Grip and referes to this particular kind of terminals and
splices in these images.
Before using this tool check that the handle color matches the barrel coclor of the
terminal to be used, check the die jaws for correct setting and condition. Now
release the lock by squeezing the handles, insert the terminal against the locator
but do not deform the barrel at this stage, insert the stripped wire into the barrel.
Hold the wire in place and start to squeeze the handles until the ratched releases,
now remove and check the crimped terminal.
Types of crimping tools
Several different types of moisture proof splices are available for applications where
a full environmental seal is required. Although different tooling methods are used,
the principle is basically the same.
The splice kit consists of an inner crimp ferrule and an outer heatshrink sealing
sleeve, impregnated at the ends with sealant, which when heated provides a full
environmental seal.
To install a moisture proof splice slide the outer sleeve over the wire, strip the wire
to the correct length and insert both wires into the crimp ferrule and check for
correct length of the stripped strands. With both wires properlay seated in the crimp
ferrule and crimp till the tool releases, slide the sleeve over the crimp and position it
in the middle. Use a heat gun to shrink the sleeve and seal the splice.
Hand crimping
The Hand Crimping Tool is designed to crimp contacts for modular terminal Blocks. It
is Used with die set S-1 and the locator SL-53. The needles are devices used to
insert and remove contacts from a Block.
AMP Stratotherm terminals and splices consist of a precision formed metal wire
barrel and a support sleeve insulated with TFE. Insulated stratotherm terminals and
splices can be divided into Pre-insulated and Post -insulated types.
The Pico Model 500D1 crimping tool is used for crimping of Flight Connector
contacts, gage 8 to 4/0. This tool operates on a supply of clean dry air or inert gas
within a pressure range of 6 to 9 bars, depending on the size of contact to be
crimped.
This is a full-cycling pneumatic tool which cannot be opened until a full crimping
cycle has been completed.
Hydraulic foot pumps are used for crimping of the following splices, connections and
terminals:
- High temperature parallel splices,
- High temperature wire splices,
- Termalum butt splices, for aluminum RB wire
- Stratotherm flag terminals,
- Copalum terminals.
The list of equipment to be calibrated lists all equipment and tools that are due for
calibration.
The list contains:
name of equipment
part or identification number
manufacturers name
equipment location
calibration procedure and manual
calibration interval
date of last calibration
date of next calibration
calibration record numbers
Here you see some examples of calibration labels. Regardless of their size, shape
and color they should bear the following information:
date of calibration
calibration record number
calibration due date
calibration inspectors signature or stamp.
You might have come across some other types of calibration labels such as:
"Calibrate prior to use" for equipment that must be checked for accuracy everytime
before you can use it.
"Reference only, not calibrated" for instruments with analog and digital readouts
that are monitored with other calibrated equipment.
And finally "Do not use" for equipment that is out of calibration and not
repaired.Calibration of Tools and Equipment
Each new tool before use shall be submitted for gauging and where applicable also
specimen checks.
Each tool shall be submitted for gauging at 1000 and 2000 crimps and for gauging
and specimen checks at 3000 crimps and all subsequent 1000 crimp checks.
All tools not in regular use shall be similarly checked every 12 months to the
gauging requirements.
3. Divide the system to find the trouble. To do this, open the system near its middle
and check the conditions there. If everything is OK at this point, the trouble is
between there and the end. If things at that point are not as they should be, the
trouble is between the power source and that point.
4. Look for the obvious problem first, and make all measurements at the points
where they are easiest to make. Popped circuit breakers, blown fuses, etc. are
usually easy to check, and are the cause of many system malfunctions.
Test Light
EWIS Troubleshooting Tools and Meters
Test light and continuity tester
The simplest electrical system troubleshooting tool is the test light. The commercial
products usually cover a range of voltages. 4) Many technicians build their own test
light with a 24Volt bulb and another one with a 115Volt bulb. The test light is handy
for determining the presence of voltage at various points in the system.
The Continuity Tester needs its own power supply - usually flashlight batteries- and
a matching bulb or a buzzer. With this device you can trace wires through a system,
locate shorts or open circuits and quickly dtermine if a fuse is good or bad. When
using a continuity tester all electrical power must be off the circuit.
Digital Multimeters.
For general purpose EWIS work, the multimeter is the instrument of choice. No other
device is able to do as much with such little investment in parts.
To measure voltage
Select volts, AC or DC as required.
Plug the black test lead into the COM input jack and the red test lead into the V
input jack.
Touch the probe tips across a load or power source as shown.
View the reading on the display.
To measure resistance.
Turn off the power to the circuit.
Select resistance - the Omega sign.
Plug the black test lead into the COM input jack and the red test lead into the Ohms
input jack.
Connect the probe tips in parallel across the portion of the circuit to be measured.
View the reading on the display.
To measure current up to a maximum of 10Amperes you can use the Multimeter. For
higher current use the Clamp-On Amperemeter discussed next in this training.
Turn off the power in the circuit.
open the circuit to connect your red lead.
Select Amperes AC or DC.
Plug the black test lead into the COM input jack and the red test lead into the
10Ampere or 300 Milliampere input jack as required.
Now connect the black lead into the circuit to close it and allow all current to flow
through the meter.
Turn on the power in the circuit.
View the reading on the display.
Clip on Ammeter
Clip-on Ammeter
A very handy tool for electrical system troubleshooting is a clip-on ammeter. This
instrument has a set of jaws that can be opened, slipped over a current carrying
wire and then clamped shut. Current flowing in the wire produces a magnetic field
that acts on a special type of semiconductor material to produce a voltage
proportional to the strength of the magnetic field. The strength of this field is
proportional to the amount of current flowing in the wire.
Clip-on ammeters are also used for troubleshooting for battery charging, starter
motors, hydraulic and fuel pumps. By clamping an ammeter over the lines to the
components, you can determine which units are operating and get an idea of the
amount of load they are carrying.
Milliohmmeter - Bonding Testers.
These instruments are used for aircraft bonding checks were very low resistances
have to be measured. Due to the very low- ohmic resistance a four pole connection
is required. The outer poles C1 and C2 provide the measuring current flow across
the test piece, Poles P1 and P2 measure the voltage drop. So called Duplex Hand
Spikes are used to perform this measurement.
Please note that the correct position of the Duplex Hand Spikes is such that the
contacts marked with "P" must always be next to each other.
Testing: In general, most bonding jumpers or ground straps must have each
connection made to have 0.003 ohms or less in resistance. This measurement must
be taken between the surface being bonded and the bonding jumper. This test may
be performed using an extremely sensitive ohmmeter or a bonding tester, and
should be done any time a connection has been modified, added to or temporarily
disconnected.
This table shows different bonding resistance values as an example. Actual values
must be taken from the maintenance manuals.
The resistance between isolated conductors must be very high, in order to prevent
leakage currents. Isolation resistances are, therefore, expressed in million ohms.
1 million ohm = 1 Mega Ohm = 1 M[Omega]
High voltages are necessary to be able to measure those high resistance values.
Isolation resistance meters have a range selector, just as multi meters.
100 V, 250 V, 500 V and 1000 V are most frequently used.
Now a few important points for measuring isolation values of wiring:
The power of the wiring to be measured must be switched off.
No equipment may be connected to the wiring at either end.
Never touch the wiring to be measured if the isolation tester is operable.
Prevent the forming of sparks in the tank when checking the isolation value of
tank wiring.
Determine the maximal measuring voltage by means of the Aircraft Maintenance
Manual or the Wiring Diagram Manual.
1. Ra-b-> Measure isolation resistance between the conductors a and b.
2. Ra-gnd -> Measure isolation resistance between conductor a and ground.
3. Rb-gnd -> Measure isolation resistance between conductor b and ground.
The obtained insulation resistance should be between 5 - 10 Mega Ohm.
Warning:
Working with high voltages can be dangerous to your health and your
surroundings.
Make sure that nobody can touch the circuit to be measured during measuring.
Make sure that the circuit to be measured cannot be damaged by the high
measuring voltage.
Always consult the Aircraft Maintenance Manual or the Wiring Diagram Manual
before performing the test.
OSILOSCOPE
Maintenance Documentation
General
The maintenance documentation supplies help for all maintenance activities. You
use many different documents to do scheduled and unscheduled maintenance. The
maintenance documents must be checked and released by the design organisation.
It must be assured that the current documents are available to the user. The
documents can be in paper form, microfilm, microfiche, electronic data carrier or online.
Supporting Data
General
The following manuals supply supporting data to carry out maintenance:
Illustrated Parts Catalog (IPC)
Wiring Diagram Manual (WDM)
Aircraft Maintenance Manual (AMM)
System Schematics Manual (SSM)
Standard Practices Manual (SPM)
Cabin Interior Manual (CIM)
Tool and Equipment Manual (TEM)
Further, there are the Master Minimum Equipment List (MMEL), the Minimum
Equipment List (MEL) and the Configuration Deviation List (CDL).
subsection or component level. According to the ATA-Specification 100 you will know
which component will be described in the named documentation.
Page Blocks
In the ATA-Specification number 100 there is a page numbering system. There are
page blocks for a special type of information. Here is a list of the page blocks: So
you can see by means of the page block system according to ATA Spec. 100 what
kind of information you will get. For example: 29-11-14 Page 301:The description of
the servicing for the filter element no. 1066 begins on this page. It describes where
to find the filter, what kind of actions have to be performed and what kind of
equipment and material has to be used.
AMTOSS
In some manuals you find an Aircraft Maintenance Task Orientated Support System
(AMTOSS). It is a standard and unique numbering system. The AMTOSS is similar to
the Page Block system, but it is a more detailed classification and description of
tasks. Tasks are procedures for specific maintenance requirements. The first 6 digits
stand for the ATA-Chapter and its system and component level. The next 3 digits
stand for the function code. This code is used to indicate the particular maintenance
function. The second three digits indicate the sequence or identification number. It
provides the numerical separation between task and subtask.
- Task identification begins at 801 and up, in sequence, to 999 within the procedure.
- Sub-task identification begins at 50 and up, in sequence, to 800 within the
procedure.
Illustrations and tables are considered as tasks. The letter of the configuration or
alphanumerical indicator indicates different modifications. The number indicates
different working methods. In the above named case the procedure has two tasks.
The first task removes the power plant and the second task installs the power plant.
This aircraft wiring schematic shows the Air Turbine Case Cooling electric circuit
from an Airbus A310 Aircraft. It is very important to first have a look at the note: at
the bottom of the diagram. According to this note all wires, unless otherwise
specified are identified by the circuit number 7523, the ATA circuit identification
number of the subsystem. The note further states that all wires have gaugenumber
16 (Kapton CF16 wire) unles otherwise specified. Try to look up the turbine case cool
engine 1 warning light on the upper left hand side of the schematic. The wire that is
coming off of terminal 3 has wire number 11 (Gauge number 24). Every time a new
diagram segment starts, the wire number changes. Notice that after the connector
the number changes to 12 and after the next connector changes again to 13 , and
then after the terminal block, to 14.
The following chart lists some of the many electrical symbols that are used in
aircraft wiring diagrams. It shows the symbol for an amplifier with the triangle
pointing in the direction of the signal or transmission. A single cell battery or a
busbar.