Cases
Instruments come in one of four different
kinds of cases.
1.
One-piece phenolic composition cases
2.
Two-piece phenolic composition cases
3.
Nonmagnetic all-metal cases
4.
Metallic-shielded cases
The cases come in several different sizes so
instruments can be easily removed and mainte-
nance simplified. Special instruments that centain
INSTRUMENT SYSTEM
mechanisms too large for adaption to a standard
MAINTENANCE
case come in specially designed cases.
Instruments easily mount on the instrument
Learning Objective: Relative to aircraft
panel with locking devices molded into the
instrument system maintenance, identify
instrument flange assembly, by spring locknuts,
the various procedures used to maintain,
or mounting clamps. You can easily remove
instruments that use a mounting clamp by
troubleshoot, test, interchange, protect,
ship, and handle aircraft instruments.
unscrewing the tension screw in the instrument's
lower right corner. You do not have to remove
You need a wide variety of skills to maintain
the tension screw to release the tension on the
aircraft instruments and their associated equip-
clamp assembly.
ment. It is important for you to check, inspect,
and maintain these instruments because the
Markings and Graduation
aircraft will not perform properly unless the
instruments present reliable information.
Markings on the glass instrument face cover
Instruments used in high-speed aircraft must
help flight personnel confirm instrument opera-
g i v e correct indications. The accuracy of
tion to within the prescribed ranges of the
instruments such as percent-type tachometers, tail
equipment. The markings usually consist of a
pipe temperature indicators, and gyro attitude
white arc on the outer edges of the instrument
indicators require preventive maintenance. The
glass. They show the normal operating range. A
existence of excessive errors in instrument systems
red mark shows the operating limit that should
directly relates to flight safety and efficient
not be exceeded.
aircraft performance. You cannot assume that
borderline instrument errors are acceptable. This
is particularly important in high-speed aircraft.
WARNING
As an AE, you will perform functional tests
on aircraft instruments to make sure they give
An index marking of white paint, not over
accurate indications. Operational and functional
one-sixteenth inch wide by three-sixteenths
tests take time. When you perform an inspection,
inch long, is at the bottom center of all
you need to know how the particular aircraft
instruments color-marked for operating
instrument operates. Also, you need to know what
ranges. Place this index mark at the point
tools and test equipment you will need. Without
between the glass and the case. This mark
these knowledge and skills, you can't properly
will show whether or not the glass cover
perform the tasks assigned to your rating.
moves at any time after marking the
ranges. Obtain the proper range markings
for the aircraft instruments from the flight
GENERAL MAINTENANCE
manual (NATOPS) for the particular
aircraft.
General maintenance of instruments fall
into two categories--scheduled and unscheduled
Panels
maintenance. The material condition of the
systems and reliability of instruments are ensured
Instrument panels are made from sheet
by the day-to-day maintenance routine.
aluminum alloy, with sufficient strength to resist
