TM 1-1510-223-10 3-58            c.   Operating Procedures. WARNING It  is  not  practical  to  provide  monitoring  for  all conceivable system failures and, it is possible that erroneous operation could occur without a fault indication. It is the responsibility of the pilot to detect such an occurrence by means of cross- checks with redundant or correlated information available in the cockpit. (1)    Equipment turn-on. The VIR-32 receiver and the CTL-32 NAV control are turned on as follows: 1.   BATTERY switch (overhead control panel, fig. 2-7) - ON. 2.   AVIONICS MASTER POWER switch (over- head control panel, fig. 2-7) - ON or EXT PWR as required. 3.   EFIS power switches (2, overhead control panel, fig. 2-7) - ON. 4.   Power and mode switch (fig. 3-25) - ON. After power is applied, the control unit displays the same active and preset frequencies that were present when the equipment was last turned off. (2)    Frequency selection.  Frequency selection is made  using  either  the  frequency  select  knobs,  or  the XFR/MEM (transfer/memory recall switch). Rotation of either frequency select knob increases or decreases the frequency  in  the  preset  frequency display.  The  larger, outer knob changes the frequency in 1-MHz increments (number to the left of decimal point). The smaller, inner knob changes the frequency in 0.05 MHz increments. After the desired frequency is set in the preset frequency display, it can be transferred to the active frequency dis- play  by  momentarily  setting  the  XFR/MEM  switch  to XFR. At the same time that the preset frequency is trans- ferred to the active display, the previously active frequen- cy   is   transferred   to   the   preset   display.   The   ACT annunciator on the control unit flashes while the receiver is tuning to the new frequency. NOTE The ACT annunciator continuing flashing indi- cates that the receiver is not turned to the fre- quency displayed in the active display. The control unit has memory that permits storing up to four preset frequencies. Once stored, these frequen- cies can be recalled to the preset display by positioning the XFR/MEM switch to the MEM position. The storage location (CH 1 through CH 4) for the recalled frequency is  displayed  in  the  active  frequency  display  while  the XFR/MEM switch is held in the MEM position. All four stored frequencies can be displayed one at a time in the preset display by repeatedly positioning the XFR/MEM switch to the MEM position. After the desired stored fre- quency has been recalled to the preset display, it can be transferred to the active display by momentarily position- ing the XFR/MEM switch to the XFR position. During normal operation, all frequency selections and revisions are accomplished in the preset frequency dis- play. However, the active frequency can be selected di- rectly   as   described   in   the   direct   active   frequency selection paragraph. (3)    Direct active frequency selection. The active frequency  can  be  selected  directly  with  the  frequency select knobs by pushing the ACT switch for about 2 sec- onds. The active frequency selection mode is indicated by dashes appearing in the preset display. Also, the ACT annunciator will flash as the frequency select knobs are turned to indicate that the receiver is being retuned. NOTE The ACT annunciator continuing flashing indi- cates that the receiver is not tuned to the fre- quency displayed in the active display. To  return  to  the  preset  frequency  selection  mode, push the ACT switch again for about 2 seconds. As a safety feature, the control unit automatically switches to the active frequency selection mode when a frequency select knob is operated while the STO, TEST, or XFR/ MEM switches are actuated. (4)    Frequency storage. Up to four preset frequen- cies can be stored in memory in the control unit for future recall. To program the memory, select the frequency in the preset frequency display using the frequency select knobs and push the STO switch once. One of the channel numbers (CH 1 through CH 4) will appear in the active display for approximately 5 seconds. During this time, the channel number can be changed, without changing the preset frequency, by momentarily positioning the XFR/ MEM switch to the MEM position. After the desired chan- nel  number  has  been  selected,  push  the  STO  switch again to store the frequency.