TM 55-1500-342-23 CHAPTER 3 WEIGHING AIRCRAFT Section I.  WEIGHING EQUIPMENT 3-1.    General.    Weighing      aircraft      with      accurately calibrated scales is the only sure method of obtaining an accurate  basic  weight  and  cg  location.    The  use  of  DD Form  365-1  and  365-3  in  accounting  for  correcting  the aircraft   basic   weight   and   cg   is   reliable   over   certain periods   of   time.      Over   extended   intervals,   however, unknown  service  weight  pickup  and  other  factors  will render the basic weight and cg data inaccurate.  For this reason,  aircraft  weighings  are  I  required  periodically  as outlined in AR 95-3.  Besides those Limes designated in the   regulations,   aircraft   will   be   weighed   when   major modifications or repairs are made when the pilot reports unsatisfactory flight characteristics, such as nose or tail heaviness, and when basic weight data reflected by DD Form  365-3  is  suspected  to  be  in  error.    In  AR  95-3, aircraft   are   classified   for   the   purpose   of   weight   and balance   control.      Reference   should   be   made   to   the regulations   since   weighing   requirements   vary   for   the different classes.  An aircraft is weighed for the purpose of   determining   its   basic   weight   and   balance.      This means  that  the  aircraft  should  be  weighed  in  its  basic condition; that is, with fixed normal equipment which is actually   present   in   the   aircraft,   less   fuel   and   other expendable    load    items.        This    does    not    preclude weighing   the   aircraft   with   expendable   load   items,   if specific   weight   of   the   items   is   available   and   proper computations    are    accomplished    to    determine    basic weight.      Supplied   with   the   basic   weight   and   balance data,  the  pilot  is  able  to  compute  the  gross  weight  and balance of his mission-ready aircraft  to  insure  safety of  flight  and   mission accomplishment. 3-2.  Weighing    Systems.  Portable-type    electronic weighing  kits  (figure  3-1)  are  normally  used  by  those activities  which  weigh  Army  aircraft.    Portable  roll  on type  scales,  stationary  pit  type  scales  or  other  devices may be used as authorized for particular aircraft models or  activities.    To  insure  accurate  results  in  determining aircraft weight, the instructions provided in the technical manuals   for   the   specified   weighing   system   must   be followed  and  the  system  must  be  properly  calibrated. For calibration requirements see TB 43-180. 3-3.    Associated  Items,  Terms,  and  Fixtures.    The description    and    definition    of    several    of    the    more important terms and fixtures are provided as follows: a.    Jacks of sufficient capacity and extension height must be used when weighing aircraft with the electronic weighing kit.  Only jacks suitable for use with either the ring or plug-type jack adapters will be used with the kit weighing cell assemblies. b.    Jig points are established during construction of an   aircraft   and   are   used   as   a   reference   for   taking measurements during weighing.  The jig point may be a hole,  fitting,  or  any  other  conveniently  fixed  station  on the aircraft.  Jig point locations are specified in Chart E data. c.    Jack  pads  are  fittings  attached  to  the  aircraft structure  which  are  used  for  reaction  or  jack  points.    A rounded or conical extension protrudes from the base of the  jack  pad  and  serves  as  the  weighing  cell  assembly or  jack  point  of  contact.    A  spherical-type  adapter  is used  to  mate  the  conical  protrusion  and  weighing  cell assembly. d.    Reaction points are those points upon which the entire   weight   of   the   aircraft   is   supported   when   scale indicator     readings     are     taken.          Most     aircraft     are supported    on    three    reaction    points;    however,    four reaction points are required for weighing some helicopters.    Typical  reaction  points  used  for  weighing aircraft are wheel, landing gear, fuselage, and wing jack pads. e.    Leveling   lugs   are   located   on   the   aircraft   to facilitate use of the spirit level in leveling aircraft. f.    Jig-located  brackets  and  plates  are  used  with the plumb bob for leveling certain aircraft. Change 5  3-1