TM 1-1520-238-10 Change 3 3-37 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. NOTE 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/ASN–137 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/ASN–128 DNS has 10 internal storage locations for coordinate data. The AN/ASN–137 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/ASN–137 DNS also uses power provided through the MUX FAB R circuit breaker on the CPG No. 1 circuit breaker panel. 3.14.4 DNS Antenna. The AN/ASN–128 and AN/ ASN–137 DNS use a common antenna (RT–1193A). 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/ASN–128 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.