TM 1-1510-223-10 (3) Modes   1,   2,   3/A,   and/or   4   operating procedure: NOTE If   the   external   security   computer   is   not installed, a NO GO annunciator will illuminate   any   time   the   Mode   4   switch   is moved out of the OFF position. 1. MASTER control - NORM. 2. M-1, M-2, M-3/A, and/or MODE 4 ON- OUT   switches   -   ON.      Actuate   only those switches corresponding to required codes. The remaining switches should be left in OUT position. 3. MODE    1    code    selectors    -    Set    (if applicable). 4. MODE   3/A   code   selectors   -   Set   (if applicable). 5. MODE     4     code     control     -     Set     (if required). 6. MODE  4  REPLY  indicator  -  Monitor  to determine    when    transponder    set    is replying to SIF interrogation. 7. MODE 4 AUDIO OUT switch - Set (as required to monitor mode 4 interrogations and replies). 8. MODE 4 audio and/or indicator - Listen and/or observe (for mode 4 interrogations and replies). 9. IDENT-MIC-OUT    switch    -    Press    to IDENT momentarily. 10. MODE     4     TEST-ON-OUT     switch     - TEST. 11. Observe that the TEST GO annunciator illuminates. 12. MODE 4 TEST-ON-OUT switch - ON. 13. ANT switch - BOT. 14. Repeat steps 4, 5 and 6.  Observe that TEST GO indicator illuminates. 15. TOP-DIV-BOT-ANT switch - TOP. 16. Repeat step 14. 17. TOP-DIV-BOT-ANT switch - DIV. 18. Repeat step 14. 19. When  possible,  obtain  the  cooperation of  an  interrogating  station  to  exercise the TEST mode.  Execute the following steps: 20. RAD TEST-OUT switch - RAD TEST. 21. Obtain   verification   from   interrogating station   that   TEST   MODE   reply   was received. 22. RAD TT-OUTI switch - OUT. (4) Transponder set identification-position operating   procedure:   The   transponder   set   can   make identification-position   replies   while   operating   in   code Modes  1,  2,  and/or  3/A,  in  response  to  ground  station interrogations.  This type of operation is initiated by the operator as follows: 1. Modes    1,    2    and/or    3/A    -    ON,    as required. 2. IDENT-OUT-MIC switch - Press momentarily to IDENT, when directed. NOTE Holding     circuits     within     the     transponder receiver-transmitter will transmit identification-position   signals   for   15   to   30 seconds.  This is normally sufficient time for ground    control    to    identify    the    aircraft's position.  During the 15 to 30 second period, it  is  normal  procedure  to  acknowledge  via the aircraft communications set that identification/    position    signals    are    being generated. Set   any   of   the   M1,   M2,   M3/A,   M-C,   or MODE     4     switches     to     OUT     to     inhibit transmission of replies in undesired modes. With the IDENT-OUT-MIC switch set to the MIC   position,   the   POS   IDENT   button   on either  control  wheel  must  be  depressed  to transmit identification pulses. (5) Shutdown procedure: 1. To   retain   Mode   4   code   in   external computer during a temporary shutdown: 2. MODE   4   CODE   switch   -   Rotate   to HOLD. 3. Wait 15 seconds. 4. MASTER control - OFF. 5. To   zeroize   the   Mode   4   code   in   the external computer, turn MODE 4 CODE switch to ZERO. 6. MASTER   control   -   OFF.      This   will automatically zeroize external computer    unless    codes    have    been retained (step 1 above). 3-34. PILOT'S BAROMETRIC ALTIMETER INDICATOR (BA-141). The  pilot'  s  barometric  altimeter  indicator  (fig.    3- 35), is a servoed unit which displays altitude information from the 3-88