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Figure 2-9.  Measuring Damage In Honeycomb Panels
Figure 2-10.  Station and Waterlines

TM-1-1520-240-BD Army CH-47D Heilcopter (NSN 1520-01-088-3869) (EIC:RCD) Manual
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TM 1-1520-240-BD (4)  In a given condition if all damages are equal to   or   less   than   the   corresponding   allowable   damage limits and the distance between damages are equal to or greater  than  the  corresponding  minimal  allowable  limit, that is, the  aircraft  may  be  released  for  flight  in  that  condition. Repair  may  be  deferred  although  some  clean-up  and smoothing    of    the    damage    will    be    required    as    will inspection for damage growth after every flight.  Special consideration should be given to damage exposed to the airstream, particularly to the effects of ram air, rain, and petaling.      Petals   may   vibrate   in   the   passing   airflow, rapidly   creating   cracks   in   the   supporting   base   metal. Large  pieces  of  metal  may  peel  off  and  damage  other parts of the aircraft.  The distance (D) between damage sites    for    most    structures    has    a    minimum    required spacing.    The  spacing  requirement  is  expressed  as  a multiple factor (N) of the measured area of damage. (a)      The   factor   applies   to   the   damage actually measured not to the maximum damage limit for the structure. (b)        The    factor    applies    to    the    largest dimension    of    the    largest    damage    between    which separation is being measured. (c)  The factor applies only if the dimensions of   both   damages,   when   added   together,   exceed   the single damage limit. (5)      Continuous   members.      Allowable   damage limits   for   caps,   longerons,   webs,   floors,   decks,   and stiffness are given throughout this section as appropriate. (6)    Damaged  fittings,  attachments,  and  splices are  classified  as  unserviceable  and  must  be  repaired, reinforced, or replaced if any of the following conditions exist: (a)      Damage   to   the   fitting   has   removed more  than  20  percent  of  the  structural  cross  section  at any one location. (b)    One  or  more  fasteners  connecting  the fitting   to   a   continuous   aircraft   component   are   bent, sheared, stripped, or loose. (c)  The fitting shows signs of overstress or structural distortion. e. General Damage Assessment. (1)  Damage Measurement. (a)    Reproduce  Figures  2-10  through  2-27 as required, and use to mark up damaged areas. (b)   Refer  to  Figures  2-10  through  2-27  for definition and identification of primary fuselage structural elements. (c)        Mark    all    detected    damage    on    the appropriate figure, and add remarks to clarify markings as described in paragraph 2-2.b(9). (d)    Refer  to  paragraph  2-2.c  and  for  each damaged   element,   measure   the   depth   "CD"   and   the length (width) "CL" or "WL" of each damage.  Count the number   of   damages   and   measure   the   "D"   between damages.    Start  with  the  worst  damage.    Record  the values   on   DA   Form   2404   (Figure   2-4)   and   compare them   with   the   allowable   damage   limits   given   in   this section.  Select the set of allowable damage limits which are  next  larger  than  the  measured  damage,  determine the corresponding condition.  Consider whether damage could result in flight failure of other elements.  Attempt to   visualize   what   effect   large   defections   of   damaged member will have on adjacent structure. (e)        Decide    on    whether    repair    can    be deferred  or  whether  damage  should  be  fixed  and  what the condition of deferred or repaired damage would be. (f)      Determine   the   priority   of   the   various required repairs based on repair time, difficulty of repair, resources  available,  tactical  situation,  and  need  for  the aircraft,  etc.    The  longest  repair  time  normally  is  given the highest priority and is most critical. (g)  Enter repair requirements on DA Forms 2404 (Figure 2-4). 2-14







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