TM 55-151 O-221 -10 placards   and   locate   exits.   An   inertia   switch,   when ORIDE  OFF  -  RESET  -  AUTO  -  TEST.  Should  the subjected to a 2 G shock, will illuminate interior lights in system  accidentally  actuate,  the  emergency  lights  will the  cockpit,  forward  and  aft  cabin  areas,  and  exterior illuminate.  Placing  the  switch  in  the  momentary  OFF lights aft of the emergency exit and aft of the cabin door. RESET  position  will  extinguish  the  lights.  To  test  the The  battery  power  source  is  automatically  recharged  by system,   place   the   switch   in   the   TEST   position.   The the  aircraft  electrical  system. lights  should  illuminate.  Moving  the  switch  to  the  OFF - RESET position will turn the system off and reset it. b.  Operation.  An  emergency  lights  override  switch, located   on   the   overhead   control   panel   (fig.   2-12),   is provided   to   turn   the   system   off   if   it   is   accidentally actuated.   The   switch   is   placarded   EMERG   LIGHTS Section   Xl.   FLIGHT   INSTRUMENTS 2-79. PITOT  AND  STATlC  SYSTEM. a.  Description,  The   pitot   and   static   system   (fig. 2-28) supplies static pressure to two airspeed indicators, the  copilot  altimeter,  the  air  data  computer  (ADC),  two vertical  velocity  indicators,  and  also  ram  air  to  the airspeed  indicators  and  the  ADC.  This  system  consists of two pitot masts (one located on each side of the lower portion   of   the   nose),   static   air   pressure   ports   in   the aircraft’s  exterior  skin  on  each  side  of  the  aft  fuselage, and  associated  system  plumbing.  The  pitot  mast  is protected  from  ice  formation  by  internal  electric  heating elements. b.  Alternate  Static  Air  Source.  An  alternate  static air  line,  which  terminates  just  aft  of  the  rear  pressure bulkhead,  provides  a  source  of  static  air  for  the  pilot’s instruments in the event of source failure from the pilot’s static air line. A control on the pilot’s subpanel placarded PILOTS  STATIC  AIR  SOURCE,  may  be  actuated  to select  either  the  NORMAL  or  ALTERNATE  air  source  by a two position selector valve. The valve is secured in the NORMAL position by a spring clip.   Refer to Chapter 7 for   airspeed   indicator   and   altimeter   calibration information  when  using  the  alternate  air  source. 2-80.  TURN-AND-SLIP  INDICATORS. Turn-and-slip  indicators  are  installed  separately  on the  pilot  and  copilot  sides  of  the  instrument  panel  (fig. 2-29).  These  indicators  are  gyroscopically  operated. They   use   DC   power   and   are   protected   by   5-ampere circuit   breakers   placarded   TURN   &   SLIP   PILOT   or COPILOT  on  the  overhead  circuit  breaker  panel  (fig. 2-26). 2-81.  AIRSPEED  INDICATORS. Airspeed  indicators  are  installed  separately  on  the pilot and copilot sides of the instrument panel (fig. 2-29). These   indicators   require   no   electrical   power   for 2-70 Change 4 operation,   The   indicator   dials   are   calibrated   in   knots from 40 to 300.   A  striped  pointer  automatically  displays the   maximum   allowable   airspeed   at   the   aircraft’s present   altitude. 2-82.  COPILOT’S  ENCODING  ALTIMETER. The copilot’s altimeter on the upper right side of the instrument   panel   (fig.   2-29)   is   a   self-contained   unit consisting  of  a  precision  pneumatic  altimeter  combined with   an   altitude   encoder.   The   display   face   indicates while,   simultaneously,   the   encoder   transmits   pressure altitude  information  to  the  INS  and  GPS.  Altitude  is displayed  by  a  10,000  foot  counter,  a  1000  foot  counter,  a 100   foot   counter,   and   a   single   needle   pointer   which indicates  hundreds  of  feet  on  a  circular  scale  in  20  foot intervals.  The  needle  pointer  is  also  coupled  to  the  100 foot  drum  counter  so  that  both  move  at  the  same  time. Below   an   altitude   of   10,000   feet,   a   diagonal   striped symbol  will  appear  on  the  10,000  foot  counter.  A barometric  pressure  setting  knob  is  provided  to  insert the desired altimeter setting in inches Hg or millibars. If AC power to the altitude encoder is lost, an OFF flag will appear in the upper center portion of the instrument face to   indicate   that   the   encoder   is   inoperative   and   the system is not reporting altitude to ground stations. 2-83.   PILOT’S   ALTlMETER   INDICATOR. The  pilot’s  altimeter,  on  the  upper  left  side  of  the instrument  panel  (fig.  2-29),  is  a  servoed  unit  under control of the Air Data Computer and is part of the Flight Director/Autopilot  System.  It  lacks  encoding  capability, but   displays   altitude   as   described   for   the   copilot’s instrument.   Operating   instructions   are   provided   in chapter  3.  When  the  BAR0  knob  is  adjusted  to  ground supplied  instructions,  the  updated  altitude  pressure  is routed to the Air Data Computer. The ADC recomputes all   data   on   hand,   sends   corrected   altitude   pressure information  to  the  Flight  Director  and  autopilot,  sends servo  commands  to  correct  the  display  on  the  pilot’s