TM  1-1520-240-10            3-3-13 (2) Present position at the time the pushbutton is released is automatically stored and the destination location is that which was displayed in the target store indicator (position 6, 7, 8 or 9) immediately before press- ing the TGT STR pushbutton. b.  Method 2. (1) MODE selector — UTM or LAT/LONG, de- pending on coordinate format desired. (2) DISPLAY selector — DEST/TGT. (3) DEST DISP thumbwheel —P. (4) KYBD pushbutton — Press when over flying potential target. Display should freeze. NOTE Do  not  press  ENT  key  while  DEST  DISP thumbwheel is at P. (5) If  it  is  desired  to  store  target,  turn  DEST DISP  thumbwheel  to  destination  location  desired  and press ENT key. (6) If it is not desired to store target, place DIS- PLAY selector momentarily to another position. 3-3-28.  Transferring Stored Target Coordinates from One Location to Another. The following procedure allows the operator to transfer stored target coordinates from one thumbwheel location to another. For example, it is assumed that the pilot wants to put the coordinates of stored target 7 into location of destination 2. NOTE Throughout  this  procedure,  range,  time-to- go,  bearing  and  left/right  steering  data  are computed and displayed for the destination selected via the FLY-TO-DEST thumbwheel. a.  DISPLAY selector — DEST/TGT. b.  DEST DISP thumbwheel — 7. c.  KYBD pushbutton — Press. d.  DEST DISP thumbwheel — 2. e.  ENT key — Press. 3-3-29.  Transferring Variation from One Location to Another. The  procedure  to  transfer  variation  data  to  the  same location where the associated stored target coordinates has been transferred is the same as in previous para- graph. Transferring Stored Target Coordinates from One Location to Another, except that the DISPLAY selector is placed at SPH/VAR. 3-3-30.  Dead Reckoning Navigation. As a BACKUP mode, dead reckoning navigation can be done using ground speed and track angle estimates pro- vided by the operator. a.  MODE selector — BACKUP. b.  DISPLAY selector — GS/TK. c.  Best estimate of ground speed and track angle — Enter via keyboard. d.  Set MODE selector to any position to abort this mode. 3-3-31.  Operation During and After Power Interrup- tion. During a DC power interruption inflight, or when all heli- copter power is removed, the random access memory (RAM) (stored destination and present position) data is retained by power from an 8.4 volt DC dry cell battery. This makes it unnecessary to reenter any navigational data  when  power  returns  or  before  each  flight.  If  the battery does not retain the stored destination data during power interruption the display will indicate an EN when power returns. This indicates to the pilot that previously stored  data  has  been  lost,  and  that  present  position, spheroid/variation,  and  destinations  must  be  entered. The computer, upon return of power, resets present posi- tion variation to E000.0, destination and associated vari- ations  to  a  non-entered  state,  sets  wind  to  zero  and spheroid  to  CL6.  The  following  data  must  be  entered following battery failure: a.  Spheroid. b.  Present position variation. c.  Present position. d.  Each destination and its associated variation. 3-3-32.  Stopping Procedure. MODE selector — OFF. 3-3-33.  Horizontal Situation Indicator (HSI). Two horizontal situation indicators (HSI) (fig. 3-3-6), one on each pilot’s instrument panel, are installed. Each indi- cator can display helicopter heading, FM homing, and position relative to a selected course or bearing. Also, during an ILS approach, the indicator displays helicopter position relative to the glide slope and localizer. The auto- matic heading select feature of the AFCS is also con- trolled through the HSI. Selection of navigational equip- ment to be displayed on each HSI is controlled through the HSI MODE SELECT panel on each instrument panel below each HSI. Each HSI receives electrical power from three different sources (copilots sources are in paren- theses): 28 volt DC from the No. 2 (No. 1) DC bus through the NAV PLT (COPLT) HSI MODE SEL circuit breaker, 115 volt AC from the No. 2 (No. 1) AC bus through the NAV PLT (COPLT) HSI circuit breaker, and 26 volt AC