TM 1-1520-240-103-3-5NOTEIf synchronizing becomes necessary in flightwith the AFCS on, position the SWIVELswitch to UNLOCK. After synchronization iscomplete, position the SWIVEL switch toLOCK. This prevents unwanted yaw axis in-puts.c. Manual Synchronization. If power has been ap-plied to the system with the compass slaving switch atFREE or if the system has been operated in the freedirectional gyro mode for a period of time, the compasscards will not be aligned with the magnetic heading of thehelicopter. The system can be reset to the correct mag-netic heading by pushing and turning the PUSH TO SETknob in the direction of the symbol indicated by the an-nunciator pointer until the pointer is centered. If the slav-ing switch is then set to SLAVED, the compass cards willmaintain correct magnetic heading.Figure 3-3-4. Directional Gyro (CN-998/ASN-43)3-3-11. Doppler Navigation Set (AN/ASN-128).NOTEWhen the Airborne Navigation Set AN/ASN-149 (Global Positioning System GPS) isinstalled, the Doppler Navigation Set AN/ASN-128 is controlled by the GPS CDU. Fora description of the Airborne navigation Setand Doppler Navigation Set.a. The doppler navigation set (fig. 3-3-5) is a self-contained navigation system that does not require anyground-based aids. The system provides worldwide nav-igation with position readout available in both universaltransverse mercator (grid) (UTM) and latitude and longi-tude (lat/long). Navigation and steering is done usinglat/long coordinates, and bilateral UTM-lat/long conver-sion routine is provided for UTM operation.b. The system in conjunction with heading data fromthe gyro compass, and pitch and roll data from the copi-lot’s attitude gyro, provides velocity, position, and steer-ing information from ground level to 10,000 feet.c. The computer-display unit (CDU) is on the cantedconsole, between the pilot and copilot positions. Coursedeviation, bearing, distance to destination, and NAV GO/NOGO are also presented to the HSI. Built in test equip-ment (BITE) continuously monitors system operation. Ifa failure occurs, a malfunction indicator lamp will lightand coded data, indicating the failed component, will bedisplayed on the CDU when the MODE switch is set toTEST. Power to operate the set is supplied by the No. 2DC bus through the NAV DOPPLER circuit breaker onthe No. 2 PDP, and the No. 1 AC instrument bus throughthe NAV DOPPLER circuit breaker on the No. 1 PDP.
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