TM 1-1500-204-23-1 tool, without demounting the tire from the wheel.  Make certain that every valve has a valve cap on it, screwed on firmly with the fingers.  The cap prevents dirt oil and moisture from getting inside the valve and damaging the core.    It  also  seals  In  air  and  serves  as  protection  in case a leak develops in the valve core. e. Installation. Install tires and tubes in accordance with the applicable maintenance manual. 9-10.  Ski Maintenance.    Maintenance  of  skis  shall  be as    specified    In    the    applicable    aircraft    maintenance manual and the following paragraphs. a. Ski  Inspection.    It  is  advisable  to  examine  ski installations   frequently   to   keep   them   maintained   in airworthy condition.  If shock cord is used to keep the ski runner  in  proper  trim,  periodically  examine  to  assure that the cord has enough elasticity to keep the runner in its required attitude and the cord is not becoming loose or   badly   frayed.      Replace   old   or   weak   shock   cords. When  other  means  of  restraint  are  provided,  examine for  excessive  wear  and  binding,  and  replace  or  repair when such conditions are found.  Examine the points of cable   attachment,   both   on   the   ski   and   the   airplane structure,  for  bent  lugs  due  to  excessive  loads  having been  imposed  while  taxiing  over  rugged  terrain,  or  by trying  to  break  loose  frozen  skis.    If  skis  which  permit attachment  to  the  wheels  and  tires  are  used,  maintain proper tire pressure, as under inflated tires may push off the  wheels.    if  appreciable  side  loads  are  developed  in landing or taxiing. b. Ski  Repair.    Aluminum  tubular  members  may have    negligible    damage    of    surface    scratches    and smooth  contour  dents  not  over  1/16  Inch  in  depth.    All damage, other than negligible, shall necessitate replacement   unless   otherwise   specified   in   applicable aircraft  maintenance  manual.    Steel  tubular  members may  have  negligible  damage  of  surface  scratches  and small  dents  not  over  0.004  inch  in  depth.    Repairable damage  shall  consist  of  straightening  slight  bends  and rewelding existing welds. 9-11.  Float Maintenance.  In order to maintain floats in an  airworthy  condition,  frequent  inspections  should  be made because of the rapidity with which corrosion takes place  on  aluminum  alloy  metal  parts,  particularly  when the  aircraft  Is  operated  in  salt  water.    Examine  metal floats and all metal parts on wooden or fiberglass floats for  corrosion  and  take  corrective  action  in  accordance with  the  applicable  aircraft  maintenance  manual.    All maintenance   of   floats   shall   be   as   specified   in   the applicable aircraft maintenance manual. 9-12.  Flight Controls.    The  flight  control  surfaces  are hinged   or   movable   airfoils   designed   to   change   the attitude   of   the   aircraft   during   flight.      Maintenance   of flight controls shall be accomplished by replacing worn, damaged,   or   defective   components,   adjusting   rigging components, and accomplishing preventive maintenance to the system. a. Types.    Ailerons,  elevators,  the  rudder,  flaps, and  trim  tabs  are  the  common  types  of  flight  controls. Each is explained in the following paragraphs. (1)   Ailerons.    The  motion  of  the  aircraft  about the  longitudinal  axis  is  called  rolling  or  banking.    The ailerons, as shown in figure 9-13, are used to control this movement.  The ailerons form a part of the wing and are located  in  the  trailing  edge  of  the  wing  toward  the  tips. Ailerons are the movable surfaces of an otherwise fixed- surface wing.  The aileron is in neutral position when it is streamlined with the trailing edge of the wing. (2)   Elevators.    When  the  nose  of  an  aircraft  is raised  or  lowered,  it  is  rotated  about  its  lateral  axis. Elevators  are  the  movable  control  surfaces  that  cause this rotation, as shown in figure 9-14.  They are normally hinged  to  the  trailing  edge  of  the  horizontal  stabilizer. The  elevator  can  be  moved  either  up  or  down.    If  the elevator  is  rotated  up,  it  decreases  the  lift  force  on  the tail causing the tail to lower and the nose to rise.  If the elevator  is  rotated  downward,  it  increases  the  lift  force on  the  tail,  causing  it  to  rise  and  the  nose  to  lower. Lowering  the  aircraft's  nose  increases  forward  speed, and raising the nose decreases forward speed. (3)   Rudder.    Turning  the  nose  of  the  aircraft causes   the   aircraft   to   rotate   about   its   vertical   axis. Rotation  of  the  aircraft  about  the  vertical  axis  is  called yawing.  This motion is controlled by using the rudder as shown In figure 9-15. (4)   Flaps.    Flaps  are  high-lift  devices  attached to  the  trailing  edge  of  the  wing.    The  flap  is  controlled from the cockpit, and when not in use fits smoothly into the   lower   surface   of   each   wing.      The   use   of   flaps increases the camber of a wing and therefore the lift of the wing, making it possible for the speed of the aircraft to  be  decreased  without  stalling.    This  also  permits  a steeper   gliding   angle   to   be   obtained   such   as   in   the landing   approach.      Flaps   are   primarily   used   during takeoff and landing.  Figure 9-16 shows various types of flaps used on aircraft. 9-12