TM 55-1510-219-10 15. ANT switch - TOP. 16. Repeat step 14. 17. 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-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 but- ton 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). 3-31.  PILOT'S ENCODING ALTIMETER. a. Description.  The encoding altimeter (fig.  326), provides  the  pilot  with  an  indication  of  present  aircraft 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 and Indicators. CONTROL FUNCTION MILLIBARS Indicates local barometric pres- indicator sure in millibars.  Adjusted by use of set knob. IN HG Indicator Indicates local barometric met- ric pressure in inches of mercu- ry.  Adjusted by use of set knob. Drum indicator Indicates aircraft altitude in ten- thousands, thousands, and hun- dreds of feet above sea level. Needle indicator Indicates  aircraft  altitude  in hundreds of feet with subdivi- sions at twenty-foot intervals. CODE OFF flag Presence indicates loss of power (pilot only) to instrument. ALT indicator Not used. Test button When  pressed,  reading should decrease by 500 feet. 3-77