TM 1-1510-218-10 8-13 NOTE To reset, turn OFF approximately 5 seconds, then ON. When  voltage  drops  below  approximately 20   volts,   the   red   anticollision   light   may become inoperative. 8-28.  BEFORE TAXIING. * 1.   BLEED AIR VALVES – As required. * 2.   BRAKE  DEICE  – As required.    To  activate the brake deice system, proceed as follows. a.   BLEED AIR VALVES – OPEN both. b.   CONDITION levers – HIGH IDLE. c.   BRAKE   DEICE   switch   –   DEICE   on. Check BRAKE DEICE light illuminated. NOTE Once brakes have been deiced, the CONDITION lever may be returned to LOW IDLE. Brake   deice   control   valves   may   become inoperative     if     valves     are     not     cycled periodically.    One  cycle  of  the  valves  is required     daily,     regardless     of     weather conditions. * 3.   CABIN    TEMP    MODE    and    temperature switches – Set as desired. NOTE For  maximum  cooling  on  the  ground,  turn the BLEED AIR VALVE switches to ENVIRO OFF position. H 4.    AC/DC power – Check as follows: a.   AC frequency – 394 - 406 Hz. b.   AC voltage – 104 -124 Vac. c.   DC load – 85% maximum per generator. d.   DC voltage – 28 - 28.5 Vdc. * 5.   AVIONICS MASTER POWER switch – ON. Do not operate radar in congested areas. CAUTION Do not operate the weather radar system in a  confined  space  where  the  nearest  metal wall  is  50  feet  or  less  from  the  antenna reflector.    Scanning  such  surfaces  within 50    feet    of    the    antenna    reflector    may damage receiver crystals. * 6.    Avionics controls – As required. NOTE The  radar  system  should  be  tested  before each  flight  on  which  the  system  is  to  be used.    If  no  significant  weather  is  in  the immediate  area  of  the  aircraft,  the  system should be left in the STBY position. H 7.   Electric elevator trim, autopilot/flight director operation  C    D1    –  When  PC  determines that an autopilot check is required, check as follows: a.   Pilot and copilot PITCH TRIM switches – Press   to   NOSE   UP   and   NOSE   DN positions, singularly and in pairs.  Check that trim wheel moves in proper direction and   operates   only   when   trim   switches are   pressed   in   pairs.      Any   deviation requires   that   electric   elevator   trim   be turned off and flight conducted using only manual trim. b.   DISC  TRIM  switch  –   Press  to  second detent    and    verify    that     electric    trim disconnects  and  that  ELEC  TRIM  light extinguishes. c.   Flight  Director  (FD)  and  Radio  Magnetic Indicator  (RMI)  warning  flags  masked  – Check. NOTE Since the pressure of airflow that normally opposes  movement  of  control  surfaces  is absent during preflight check, it is possible to     get     a     hard     over     control     surface deflection    if    an    autopilot    command    is allowed to remain active for any appreciable length of time.  Move turn knob and   pitch   thumbwheel    only    enough    to check  operation,  then  return  them  to  the center position. d.   Select HDG mode – Check. WARNING