TM 55-1510-220-10 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: a. RAD     TEST-OUT     switch     RAD TEST. b. Obtain verification from interrogating station that a TEST MODE reply was received. c. RAD TEST-OUT 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. NOTE Set  any  of  the  M1,  M2,  M3/A,  M-C,  or MODE    4    switches    to    OUT    to    inhibit transmission of replies in undesired modes. NOTE With  the  IDENT-OUT-MIC  switch  set  to the  MIC  position,  the  POS  IDENT  button must be depressed to transmit identification pulses. (5) Shutdown procedure: (a) To   retain   Mode   4   code   in   external computer during a temporary shutdown: 1. MODE  4  CODE  switch  Rotate  to HOLD. 2. Wait 15 seconds. 3. MASTER control OFF. 4. To zeroize the Mode 4 code in the external computer turn MODE 4 CODE switch to ZERO. 5. MASTER  control  OFF.    This  will automatically zeroize the external computer unless codes have been     retained     (step     1. above). d. Transponder Emergency Operation.  Not applicable. 3-32.   PILOT’S ENCODING ALTIMETER. a. Description.    The   encoding   altimeter   (fig.      328), provides   the   pilot   with   an   indication   of   present   aircraft pressure altitude above sea level. It also supplies information to  the  transponder  for  Mode  C  (altitude  reporting)  operation and  to  the  aided  inertial  navigation  system.    The  circuit  is protected   by   the   5-ampere   PILOT'S   ALT   ENCD   circuit breaker   on   the   overhead   circuit   breaker   panel   and   the   1- ampere F21 fuse in the No.  1 junction box. b. Controls/Indicators and Functions. (1) MILLIBARS window. Indicates local barometric pressure in millibars.  Adjusted by use of set knob. (2) IN  HG  window.     Indicates  local  barometric pressure in inches of mercury.  Adjusted by use of set knob. (3) Drum indicator.  Indicates aircraft altitude in ten-thousands,   thousands,   and   hundreds   of   feet   above   sea level. 3-83