tip curling within a one-half inch square area on the leading  edge of the blade tip is usually acceptable if the curling is not  sharp. Curling is acceptable on the trailing edge if it does not  extend beyond the allowable area. Any sharp bends that may  result in cracking or a piece breaking out of the turbine blade  is cause for rejection, even though the curl may be within  the allowable limits. Each turbine blade should be inspected  for cracks. Turbine blades are generally replaceable, subject to moment- weight limitations. These limitations are contained in the  engine manufacturer’s applicable technical instructions. If  visual inspection of the turbine assembly discloses several  broke n, cracked, or eroded blades, replacing the entire  turbine assembly may be more economical than replacing  the damaged blades.  [Figure 10-67]  In the initial buildup of the turbine, a complete set of 54  blades made in coded pairs (two blades having the same  c ode  letters) is laid out on a bench in the order of diminishing  moment-weight. The code letters, indicating the moment- weight balance in ounces, are marked on the rear face of the  fir-tree section of the blade (viewing the blade as installed  at final assembly of the engine). The pair of blades having  the heaviest moment-weight is numbered 1 and 28; the  next heaviest pair of blades is numbered 2 and 29; the third  heaviest pair is numbered 3 and 30. This is continued until  10-52 Figure 10-66.  Typical turbine blade inspection.  Figure 10-65.  Turbine blade waviness.  Turbine Blade Replacement Procedure ½" ½" ¼" Nicks at tip edge not critical blend raised edge only Examine carefully for indication  of cracks at edges of fir-tree  serrations. Reject for any indication of cracks. Tip curling permissible in these areas, if under certain circumstances. Nicks over .008-inch deep are cause for rejection except that if nicks are slightly deeper than .006-inch but do not exceed .012-inch in depth and are well away from the lead or trail edge the blade is acceptable for continued use. Nicks on the convex surface away from the leading  and the trailing edges need not be completely  blended out. Same for the concave surface. Nicks on the trailing edge must be  completely removed. If too much  material must be removed, reject blade. Entire trailing edge is critical area. Nicks at outer tip end not as critical as  nicks nearer the root end, since the  nearer the root end, the greater the  moment-weight tending to produce a  crack. Nicks that “come through” to underside  of blade are cause for rejection. Nicks on the leading edge  must be completely blended  out. If too much material must  be removed, reject blade.