Low battery charge. A low battery unit
charge will cause INS to shut down when INS is operating on
battery unit power. Both WARN annunciator on CDU and
BAT annunciator on MSU will illuminate and not extinguish
until the mode selector is set to OFF. The battery unit should
be replaced when this failure occurs.
Interpretation of failure indications. It
is important to be able to correctly interpret failure
indications in order to take effective action. Failure
indications are listed below under two main categories:
WARN annunciator illuminated, and WARN annunciator
extinguished. Under each of these categories are listed other
information to take action.
WARN annunciator illuminated. Take
the following action:
If action codes 01, 02, 03, 04 or 05
are displayed See table 3-2.
No action or malfunction codes
displayed Indicates NAV unit computer
Improper displays Indicates NAV
unit computer failure.
WARN annunciator extinguished. If
CDU displays are blank, incorrect or
frozen CDU failure is indicated.
It is not possible to load displays from the
keyboard. A temporary failure of a
numerical key may prevent loading. If a
number cannot be loaded into latitude or
longitude displays, after pressing/wiggling
the key several times, the cause may be the
momentary hang-up of another key. To
identify the faulty key, rotate the data
selector to DSRTK/STS. The right digit on
right display will indicate suspect key.
Press and release suspect key several times.
To test whether the keyboard problem is
numerical key. Its number should now
appear as the right digit. If this test is
successful, press the CLEAR key and
return data selector to original data
position. Otherwise, a CDU failure is
CDU BAT indicator annunciator is
Operation on battery is an indication that
there may not be aircraft power to blower
motor with resultant loss of cooling. The
INS can operate only a limited time
(normally 15 minutes) on battery power be
Table 3-2. Malfunction Code Check
Rotate to DSRTK/STS
RH data display
Action code second and third digits
Press and release
RH data display
Lowest number malfunction code which
has occurred since this procedure was
performed replaces action code.
Repeat step 3 repeatedly, recording all malfunction codes until second and third digits again indicate
an action code or go blank. Refer to Table 34 for action codes and recommended action and to Table
3-5 for malfunction code definition.
If WARN light extinguishes and two digits go blank, failure was intermittent and has been cleared. If
digits do not go blank, perform action according to displayed recommended action code.
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