TM  55-1510-221-10 3-1)   -  No.2  position,  or  radio monitor  control  No.2  -ON. 3.  Manual  frequency/preset  channel selectors - Set desired frequency. 4. Volume control - As required. (3.)  Transmitter  operating  procedure: 1. Transmitter-interphone selector switch  (audio  control  panel,  fig. 3-1) - No.2 position. 2.  Microphone  switch  -  Press. (4.)   Shutdown   procedure:   Mode   selector switch (fig. 3-5) - OFF. d. VHF AM-FM Emergency Operation: (1.)   Emergency   AM   Mode: 1.   Transmitter-interphone selector switch  (audio  control  panel,  fig. 3-1) - No.2 position. 2. Mode selector switch - TR. 3.  Frequency control/emergency selector switch - EMER AM. NOTE Selecting EMER AM or FM automatically disables  secure  speech  function  and enables normal voice communication. 4.  Microphone  switch  -  Press. (2.)   Emergency   FM   Mode: 1. Transmitter-interphone selector switch  (audio  control  panel,  fig. 3-1) - No.2 position. 2. Mode selector switch - TR. 3.  Frequency control/emergency selector switch - EMER FM. 4.  Microphone  switch  -  Press. (3.)  Shutdown  Procedure:  Shutdown  mode select switch - OFF. 3-12.  VOICE  SECURITY  SYSTEM  TSEC/KY-28 (PROVISIONS  ONLY) NOTE Voice  security  system  TSEC/KY-58  may be installed in lieu of voice security sys- tem   TSEC/KY-28.   Complete   provisions are  provided  to  install  either  the  KY-28 or the KY-58 voice security system on the LH  fwd  avionics  rack  behind  the  pilot (fig. 2-2). a. Description.  The KY-28 voice security sys- tem provides secure (ciphered) two-way voice com- munications for the pilot and copilot in conjunction with  the  UHF  and  VHF/AM/FM  command  sets, and the backup VOW set. System circuits are pro- tected  by  the  VHF,  VHF/AM/FM,  RADIO  RELAY, and BU VOW circuit breakers on the overhead cir- cuit breaker panel (fig. 2-26). Figure 3-6 illustrates the  KY-28  voice  security  (CIPHONY)  control  indi- cator. b.  Controls/Indicators  and  Functions.  Voice security   control/indicator   (LH   fwd   avionics   rack behind the pilot) (fig. 2-2). Off. (1.)  POWER  ON  switch.  Turns  set  on  or NOTE The  POWER  ON  switch  must  be  in  ON position for FM liaison or secure mission operations  in  either  the  plain  or  cipher mode. (2.)   POWER   ON   indicator.   Illuminates when POWER ON switch is placed in ON (up) posi- tion. (3.)  PLAIN  indicator.  Illuminates   when PLAIN/CIPHER switch is in PLAIN position. (4.)  PLAIN/CIPHER  switch. (a.)  PLAIN.  Enables   unciphered communications on FM liaison set. (b.) CIPHER.  Enables  ciphered  com- munications on FM liaison set. (5.)  RE-X/REG  switch. (a.)  RE-X.  Enables   re-transmission of  ciphered  communications  at  a  distant  location. (b.)  REG.  Enables  normal  cipher  or plain communications. (6.)  ZEROIZE  switch.  Normally  OFF. Place  in  ON  position  during  emergency  situations  to neutralize   and   make   inoperative   the   associated cipher   equipment. (7.)  CIPHER  indicator.  Illuminates   when PLAIN/CIPHER switch is in CIPHER position. 3-12