place that spheroid is input is the DNS. Only 1 spheroid
can be utilized by the DNS. The DNS PPOS and destina-
tion spheroids must be the same. The DEK SP1 and DNS
PPOS spheroid must be the same.
3.14.3 Doppler Navigation Sets.
The non integrated navigation system uses
one of two Doppler Navigation Sets (DNS):
AN/ASN-128 or AN/ASN-137 for navigation.
The DNS which is installed may be deter-
mined by which Computer Display Unit
(CDU) is installed in the CPG right-hand
console. The CDU (fig 3-11) identifies those
helicopters equipped with the AN/ASN-128
DNS. The CDU (fig 3-12) are those helicop-
ters equipped with the AN/ASN-137 DNS.
The CDU used with the AN/ASN137 DNS
is not part of the DNS, but is used to com-
municate with the DNS.
The DNS provides doppler velocity, and navigational posi-
tion and steering information for the helicopter. The DNS
is the navigator in the non integrated system. The HARS
provides attitude reference (heading, pitch, and roll) to the
DNS. Navigational accuracy may degrade at altitudes
above 10,000 feet AGL, and at pitch and roll angles great-
er than 30 degrees. The DNS is capable of providing posi-
tion readouts in either the Military Grid Reference System
(MGRS) form of Universal Transverse Mercator (UTM) or
in latitude and longitude (LAT/LONG) coordinates. Navi-
gation calculations are accomplished by the DNS in LAT/
LONG and then converted to UTM (if necessary) for dis-
play purposes. Coordinate data may be entered in either
coordinate format. The AN/ASN128 DNS has 10 internal
storage locations for coordinate data. The AN/ASN137
DNS has 20 storage locations. Primary power to operate
the DNS is provided through the DPLR circuit breaker on
the pilot overhead circuit breaker panel. In addition, the
AN/ASN137 DNS also uses power provided through the
MUX FAB R circuit breaker on the CPG No. 1 circuit
3.14.4 DNS Antenna.
The AN/ASN128 and AN/
ASN137 DNS use a common antenna (RT1193A). The
DNS antenna is located in a combined antenna/radome
and (RT) housing protected by the fairing on the bottom
center fuselage area as shown in figure 3-1.
3.14.5 AN/ASN128 DNS Controls and Displays. The
controls and displays are on the front of the CDU CP1252
(fig 3-11) located on the CPG right console. The function
of each control is described in table 3-12 .
3.14.6 Modes of Operation.
The three basic modes of
operation are as follows:
a. Test Mode. The TEST mode contains two func-
tions: LAMP TEST mode, in which all display segments
are lit, and TEST mode, in which system operation is veri-
fied. In the LAMP TEST mode. system operation is identi-
cal to that of navigate mode except that all lamp segments
and the MEM and MAL indicator lamps are lighted to
verify their operation. In TEST mode, the system antenna
no longer transmits or receives electromagnetic energy;
instead, self-generated test signals are inserted into the
electronics to verify operation. System operation automat-
ically reverts into the backup mode during test mode. Self-
test of the DNS is done using Built-In-Test Equipment
(BITE) and all units connected and energized for normal
operation. Self-test isolates failures to one of the three
units of the DNS. The CDU (except for the keyboard and
display) is on a continuous basis, and any failure is dis-
played by turn-on of the MAL indicator lamp on the CDU.
The signal data converter and (RTA) are tested by turning
the MODE selector switch to TEST. Failure of these com-
ponents is displayed on the CDU by turn-on of the MAL
indicator lamp. Identification of the failed unit is indicated
by a code on the display panel of the CDU. Continuous
monitoring of the signal data converter and RTA is pro-
vided by the MEM indicator lamp. The MEM indicator
lamp will light in normal operation when flying over smooth
water. However, if the lamp remains lighted beyond 10
minutes over land or rough water, there is a malfunction in
the doppler set. Then, to determine the nature of the mal-
function, the operator should turn the MODE selector
switch to TEST. As the keyboard is used, operation is veri-
fied by observing the alphanumeric readout.