TM 1-1520-238-10
3-42
Change 3
Table 3-13.
AN/ASN-128 Window Displays
DISPLAY
REMARKS
LEFT
RIGHT
GO
No display.
Display
blank is
(normal).
If right display is blank, system is operating satisfactorily.
GO
P
If right display is P, then pitch or roll data is missing, or pitch exceeds 90 deg. In this
case, pitch and roll in the computer are both set to zero and navigation continues in a
degraded operation. Problem may be in the HARS or helicopter cabling.
NOTE
If the TEST mode display is BU, MN or NG, the MODE switch should be recycled
through OFF to verify that the failure is not a momentary one. If the TEST mode display
is BU or MN, the data entry may be made in the UTM or LATT/LONG mode: but any
navigation must be carried on with the system in the BACKUP mode
BU
C,R,S, or H
followed by
a numeric
code
A failure has occurred and the system has automatically switched to a BACK-UP mode
of operation as follows:
1. If no true airspeed is available, last remembered velocity is being used for navigation.
2. The operator has the option of turning the MODE switch to BACKUP and entering the
best estimate of ground speed and track angle.
3. If true airspeed is available, true airspeed plus remembered wind is used for
navigation.
NOTE
The operator has the option of turning the MODE switch to BACKUP and entering his
best estimate of wind speed, direction, ground speed, and track angle. The operator
should update present position immediately because it is possible that significant
navigation errors may have accumulated.
MN
C,R,S, or H
followed by
a numeric
code
A failure has occurred and the BACKUP mode, used for manual navigation (MN), is the
only means of valid navigation. The operator may use the computer as a dead reckoning
device by entering ground speed and track data. The operator should update present
position immediately because it is possible significant navigation errors may have
accumulated.
NG
C,R,S, or H
followed by
a numeric
code
A failure has occurred in the system and the operator should not use the system.
EN
The 9 V battery has failed. All stored data must be reentered. This display may be
cleared by pressing the KYBD pushbutton.
