text: Appendix A
  A-93. The decision on where to place or even whether to use a FSCL requires careful consideration. If used,
  its location is based on estimates of the situation and concept of operations. The establishment of a FSCL
  does not create a free-fire area (FFA) beyond the FSCL. Engagements beyond the FSCL must be consistent
  with the establishing commander's priorities, timing, and desired effects. Location of enemy forces,
  anticipated rates of movement, concept and tempo of the operation, organic weapon capabilities such as wide-
  area munitions, or those with delayed effects, and other factors are all considered by the commander. The
  establishing commander adjusts the location of the FSCL as required to keep pace with operations. A series
  of disseminated "on-order" FSCLs will help accelerate the coordination required. The establishing
  commander quickly transmits the change to higher, lower, adjacent, and supporting headquarters to ensure
  that appropriate controlling agencies coordinate engagement operations. Changes to the FSCL require
  notification of all affected forces within the AO and must allow sufficient time for these forces and/or
  components to incorporate the FSCL change. Current technology and collaboration tools between the
  elements of the joint force determine the times required for changing the FSCL. The FSCL is normally
  positioned closer to the forward line of own troops in the defense than in the offense; however, the exact
  positioning depends on the situation. Placing the FSCL at greater depths will typically require support from
  higher headquarters and other supporting commanders. Also, when the FSCL is positioned at greater depth,
  there is greater requirement for detailed coordination with the establishing commander and can slow the
  expeditious clearance of fires short of the FSCL. By establishing a FSCL close in, yet at sufficient depth so
  as to not limit high tempo maneuver, land and amphibious force commanders ease the coordination
  requirements for engaging targets within their assigned areas by forces not under their control, such as naval
  surface fire support or air interdiction.
  Note. During large-scale combat operations, it is likely that divisions and corps are operating as a
  tactical headquarters and will only provide input on proposed FSCL locations to the land
  component commander.
  Free-Fire Area
  A-94. A free-fire area is a specific region into which any
  weapon system may fire without additional coordination with
  the establishing headquarters (JP 3-09). Where indirect fires
  and aircraft share a FFA, units should establish an airspace
  coordination area to assist in deconflicting operations.
  Normally, division or higher echelon headquarters establish a
  FFA on identifiable terrain. Figure A-45 depicts a FFA.
  Figure A-45. Free fire area
  Kill Box
  A-95. A kill box is a three-dimensional permissive fire support coordination measure with an associated
  airspace coordinating measure used to facilitate the integration of fires (JP 3-09). It is used to facilitate
  integrating joint fires and coordinating associated airspace. The two types of kill boxes are blue kill box and
  purple kill box. A blue kill box facilitates the attack of surface targets with air-to-surface munitions without
  coordination with the AO commander’s headquarters. Within its boundaries a blue kill box extends from the
  surface to a ceiling altitude agreed upon by the requesting unit, AO commander, and airspace control
  authority. A purple kill box facilitates the attack of surface targets with subsurface-to-surface, surface-to-
  surface, and air-to-surface munitions without coordination with the AO commander’s headquarters. Within
  its boundaries a purple kill box extends from the surface, through an airspace coordinating measure floor to
  a ceiling altitude agreed upon by the requesting unit, AO commander, and airspace control authority.