TM 55-1500-342-23 NOTE Before    attempting    to    raise    an aircraft,   relative   heights   of   main and nose or tail landing wheels in both three-point and level attitudes should be considered in order    to    determine    the    proper blocking,    lifting,    and/or    jacking equipment required.  Raising a tail wheel  to  level  an  aircraft  may  be quite  a  problem  unless  adequate lifting,   hoisting,   and   supporting equipment    is    available.        Jacks should  never  be  employed  at  any place   on   the   aircraft   other   than specified jacking points. CAUTION Excessive  side  loads  may  cause cell breakage and incorrect readings.      If   wing   and   fuselage jacks are used to level the aircraft, shock struts must be restrained to prevent them from extending when aircraft is raised. CAUTION During leveling procedure, extreme care should be exercised to   avoid   side   loads   which   may cause the aircraft to slip off jacks. For example, when wing jacks are in  place  while  tail  is  lifted  to  the level position, it is likely that side loads   caused   by   rotation   of   the fuselage  will  cause  jacks  to  slip off the jack points causing severe damage    to    the    wing.        Correct procedure requires that the tail be lifted while the aircraft is supported    on    main    gear    with brakes   unlocked.      When   raising the  aircraft  with  two  wing  or  two main  landing  gear  jacks  be  sure that   the   two   jacks   are   actuated simultaneously in order to maintain   the   aircraft   in   a   lateral level attitude. e.    Level     aircraft     in     accordance     with     aircraft maintenance manuals. f.    Measure and record dimensions once aircraft is in a level position.  Three horizontal dimensions must be either  measured  or  otherwise  known  to  determine  the horizontal location of the center of gravity of the aircraft as  weighed.    When  landing  gear  are  used  as  reaction points, dimensions to be determined are as follows: (1) The horizontal distance from the reference   datum   to   some   known   jig   point.      It   is   not necessary   to   measure   this   distance   as   it   is   given   in Chart E data and will remain fixed. (2) The distance from the jig point to a lateral line   passing   through   the   main   reaction   points.      This measurement   must   be   made   along   a   line   which   is parallel to the longitudinal axis of the aircraft. (3) The  wheel  base  or  distance  between  the main and forward or aft reaction points. g.    Measure  dimension  in  steps  f(2)  and  (3)  above by projecting required points to hangar floor.  Project jig point  to  hangar  floor  by  suspending  a  plumb  bob  from center  of  jig  point  so  that  plumb  bob  is  approximately 1/2  inch  above  floor.    Wait  until  swing  of  plumb  bob stops, and make a cross mark on floor directly under tip of  plumb  bob.    Print  words  JIG  POINT  near  cross  on floor to distinguish it from other projected points.  Main reaction  points  are  projected  in  the  same  manner  as described above for the jig point.  After marking crosses for the two main reaction points, stretch a chalked string between them and draw taut.  Snap string against floor, leaving a clear straight chalk line between main reaction points.      Nose   or   tail   reaction   point   is   projected   in   a similar manner to plumb bob method. h.    Move plumb bob line a short distance fore or aft (in  a  direction  parallel  to  longitudinal  axis  of  aircraft) when  jacks  or  other  obstructions  interfere  with  free  fall of   plumb   bob.      Plumb   bob   will   then   swing   free   of obstructions.    Drop  plumb  bob  and  mark  floor  contact point.  Measure distance necessary to move plumb line; be   sure   to   correct   for   this   transferred   distance   when recording measurements on DD Form 365-2. i. Measure required dimensions after these points are projected to floor.  Dimensions to be measured are listed as B and D on DD Form 365-2.  Distance B is the same  dimension  as  discussed  in  step  f(2)  above.    It  is the perpendicular distance from the projected jig point to the    chalk    line    between    the    main    reaction    points. Distance D is the same dimension as referred to in step f(3)  above.    It  is  the  wheel  base,  or  distance  from  the centerline of the main reaction points to the nose or tail Change 1  3-4