abilities since there are few aircraft systems in-
materials known as flammable or combustible
dependent of electrical operations. In addition,
materials.
many troubleshooting charts call for continuity
2. Toxic and poisonous materials (TOXIC).
checks that a properly trained AD can easily
The word TOXIC identifies lines that contain
accomplish.
materials that are extremely hazardous to life or
health.
3 . Anesthetics and harmful materials
NOTE: Only authorized personnel may
(AAHM). The AAHM markings identify lines
repair and maintain electronic and elec-
trical equipment because of the chance of
containing materials that produce anesthetic
injury, the danger of fire, and possible
vapors and all liquid chemicals that are hazardous
material damage. To use electrical test
to life and property. These materials do not
produce dangerous quantities of fumes or vapors.
equipment correctly, you need to have a
4. Physically dangerous materials (PHDAN).
working knowledge of basic electricity.
You should adhere to the special and
The PHDAN marking identifies lines that carry
general rules for the handling of electrical
a material that is not dangerous within itself but
is asphyxiating in confined areas. The material in
devices.
the line may be in a dangerous physical state of
high pressure or temperature.
GENERAL RULES FOR ELECTRICAL
Aircraft and engine manufacturers are
TEST METERS
responsible for the original installation of
Always connect an ammeter in series--never
identification markers, and maintenance person-
nel are responsible for replacement as necessary.
in parallel. Always connect a voltmeter in
Tapes and decals are on both ends of a line and
parallel--never in series. Never connect an
ohmmeter to an energized circuit. On test meters,
at least once in each compartment through which
select the highest range first, then switch to lower
the line passes. In addition, identification markers
ranges as needed.
are found next to each valve, regulator, filter, or
When you use an ohmmeter, select a scale that
other accessory within a line. Location require-
ments are the same for tapes and decals as they
gives a near midscale reading. Midscale is the
point where the meter is most accurate. Do not
are for tags and paint.
leave the multimeter selector switch in a resistance
Additional information is listed in Aviation
position when the meter is not in use. The leads
Hose and Tube Manual, NAVAIR 01-1A-20.
may short together, discharging the internal
Complete instructions for installing fluid line
identification markers are contained in MIL-
battery. There is less chance of damaging the
meter if the switch is on a high at-volt setting,
STD-1247B.
or in the OFF position. Meters that have an OFF
position dampen the swing of the needle by con-
necting the meter movement as a generator. This
GAS TURBINE TEST EQUIPMENT
prevents the needle from swinging wildly when
You will find that certain test equipment will
moving the meter.
View the meter from directly in front to
prove invaluable in troubleshooting engine
eliminate parallax error. Observe polarity when
systems. We will briefly discuss the necessary test
measuring dc voltage or current. Do not place
equipment available for maintaining aircraft
systems. More detailed information can be found
meters in the presence of strong magnetic fields.
Never measure the resistance of a meter or a
in the technical manual for the particular piece
circuit with a meter in it. The high current required
of equipment.
for ohmmeter operation may damage the meter.
This also applies to circuits with low-filament-
ELECTRICAL TEST EQUIPMENT
current tubes and to some types of semi-
conductors.
During troubleshooting, you will often
When you are measuring high resistance, do
measure voltage, current, and resistance.
not touch the test lead tips or the circuit because
Although AEs normally troubleshoot and repair
it may cause body resistance to shunt the circuit,
electrical systems, you should have a knowledge
causing an erroneous reading. Connect the ground
of basic electricity and test equipment. This
lead of the meter first when making voltage
knowledge will increase your troubleshooting
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