TM 1-1510-218-10 2-134 b.  Replenishing Oxygen System. 1.   Remove oxygen access door on outside of aircraft. 2.   Remove protective cap on oxygen system filler valve. 3.   Attach oxygen hose from oxygen servicing unit to filler valve. If the oxygen system pressure is below 200 psi,   do   not   attempt   to   service   system.   Make an entry on DA Form 2408-13-1. 4.   Ensure  that  supply  cylinder  shutoff  valves on the aircraft are open. 5.   Slowly   adjust   the   valve   position   so   that pressure increases at a rate not to exceed 200 psi per minute. 6.   Close pressure regulating valve on oxygen servicing   unit   when   pressure   gauge   on oxygen    system    indicates    the    pressure obtained using the Oxygen System Servicing Pressure Chart, Figure 2-24. NOTE To compensate for loss of aircraft cylinder pressure  as  the  oxygen  cools  to  ambient temperature  after  recharging,  the  cylinder should be charged initially to approximately 10% over prescribed pressure.  Experience will determine what initial pressure should be used to compensate  for  the  subsequent  pressure loss   upon   cooling.      A   small   top-off   will create little heat.  A complete recharge will create substantial heating. The     final     stabilized     cylinder     pressure should be adjusted for ambient temperature, Figure 2-24. 7.   Disconnect    oxygen    hose    from    oxygen servicing unit and filler valve. 8.   Install    protective    cap    on    oxygen    filler valve. 9.   Install oxygen access door. 2-115.  GROUND HANDLING. Towing  lugs  are  provided  on  the  upper  torque knee fitting of the nose strut.  When it is necessary to tow the aircraft with a vehicle, use the vehicle tow bar. 1.   Do  not  attempt  towing  or  taxiing  of  the aircraft     with     control     surfaces     in     the LOCKED position. 2.   Do    not    operate    engines    while    towing equipment  is  attached  to  the  aircraft,  or while the aircraft is tied down. 3.   When moving the aircraft, do not push on propeller  deicing  boots.    Damage  to  the heating elements may result. 4.   When    the    aircraft    is    being    towed,    a qualified person shall be in the pilot's seat to maintain control by use of the brakes. 5.   When  towing,  do  not  exceed  nose  gear turn  limits.    Avoid  short  radius  turns,  and always   keep   the   inside   or   pivot   wheel turning during the operation. 6.   When   being   moved   backwards,   do   not apply the brakes abruptly. 7.   Tow  the  aircraft  slowly,  avoiding  sudden stops,  especially  over  snowy,  icy,  rough, soggy or muddy terrain. 8.   Do   not   tow   aircraft   with   deflated   shock struts. 2-116.  GROUND    HANDLING    UNDER    EXTREME WEATHER CONDITIONS. Extreme weather conditions necessitate particular  care  in  ground  handling  of  the  aircraft.    In hot,  dry,  sandy,  desert  conditions,  special  attention shall be devoted to finding a firmly packed parking and towing  area.    If  such  areas  are  not  available,  steel mats or an equivalent solid base shall be provided for these purposes.  In wet, swampy areas, care shall be taken to avoid bogging down the aircraft.  Under cold, icy,  arctic  conditions,  additional  mooring  is  required, and    added    precautions    shall    be    taken    to    avoid skidding   during   towing   operations.      The   particular problems  to  be  encountered  under  adverse  weather conditions and the special methods designed to avoid damage   to   the   aircraft   are   covered   by   the   various phases of the ground handling procedures included in this  section  of  general  ground  handling  instructions.   (Refer to TM 1-1500-204-23). WARNING