text: Appendix A
  A-86. Commanders designate a PL as the
  trigger line for available supporting fire support
  systems. They base the location of the trigger
  line on the mission variables, including such
  variables as the time of flight for artillery
  shells, positioning of the guns, and the
  existence of quick-fire links. The trigger line’s
  location varies from situation to situation. Its
  position reflects the distance an enemy force is
  likely to traverse in the time it takes from when
  fires are requested to when artillery rounds
  impact at a given enemy’s movement speed.
  This gives time for supporting fire support
  systems to respond to the initial call for fire. For
  example, in a desert environment an enemy
  force is expected to travel two kilometers in
  three minutes. The battalion creates an indirect
  fire trigger line that is approximately two Figure A-42. Trigger line
  kilometers beyond the point where the
  commander wants to engage enemy forces with indirect fires since it takes three minutes to process a call for
  fire and for rounds to impact. Figure A-42 depicts both direct fire and fire support trigger lines based on
  enemy movement.
  A-87. Commanders can establish another trigger line for the unit’s most accurate long-range weapon system
  in the vicinity of the area where the fire support impacts to capitalize on the asymmetric attack. However,
  dust and debris resulting from the artillery fire may prevent direct fire systems from engaging enemy forces.
  Commanders establish other trigger lines and TRPs for shorter-range systems. Commanders may give
  guidance to extremely proficient crews to engage enemy forces at longer than normal ranges or give them
  different engagement priorities than the rest of the force, such as giving priority to engaging air defense or
  engineer breaching systems.
  A-88. As enemy forces advance, commanders establish a decision point to help force a determination on
  whether to continue to fire in depth or to concentrate unit fires on a single point. Many factors impact this
  decision, most of which concern enemy forces regarding their methods of maneuver and the effects of the
  defending force’s fires.
  COMMON FIRE SUPPORT COORDINATION MEASURES
  A-89. Commanders employ FSCMs to facilitate rapid target engagement and simultaneously provide
  safeguards for friendly forces. The fire support coordinator recommends FSCMs to the commander based on
  the commander’s guidance, location of friendly forces, scheme of maneuver, and anticipated enemy actions.
  Locations and implementing instructions for FSCMs are disseminated electronically and via overlays through
  command and fire support channels to higher, lower, and adjacent units. Once established, FSCMs are entered
  into or posted on all the command’s displays and databases. Below are some of the most commonly used
  FSCMs. FSCMs are either permissive or restrictive. (See ADP 3-19 and FM 3-09 for a detailed explanation
  on the use of all FSCMs.)
  PERMISSIVE FIRE SUPPORT COORDINATION MEASURES
  A-90. Permissive FSCMs facilitate the attack of surface targets. Permissive FSCMs do not include the
  clearance of airspace and all fires require terrain and airspace clearance prior to engagement. FSCMs will
  change frequently during operations and the commander adjusts FSCMs as required to keep pace with
  operations Common permissive FSCMs include a coordinated fire line (CFL), a fire support coordination
  line (FSCL), kill box, and a free-fire area (FFA).