text: Chapter 5
  duration, and orientation of the screen), the time needed to occupy the observation posts and to establish the
  screen, and the ability of indirect fire assets to range NAIs and TAIs to provide security to the protected force.
  Both BCT and squadron commanders and staffs consider conditions to facilitate reconnaissance handover or
  battle handover with the BCT. The commanders consider the time required to conduct the handover along
  with the time and distance needed for subordinate elements to maneuver to subsequent positions.
  5-25. A rearward passage of lines is similar in concept to a forward passage of lines. A rearward passage of
  lines continues the defense or retrograde operation and maintains enemy contact while allowing for recovery
  of security or other forward forces. A unit may or may not conduct rearward passage of lines under enemy
  pressure. Usually, the stationary unit assumes control of the area of operations forward of the battle handover
  line (BHL) after two-thirds of the passing force’s combat elements move through the passage points. A battle
  handover line is a designated phase line where responsibility transitions from the stationary force to the
  moving force and vice versa (ADP 3-90). Cavalry squadrons and security forces conduct extensive
  coordination enabling rearward passage of lines, especially while under fire. Passage of lines may occur
  during any reconnaissance or security operation. (Refer to FM 3-90-2 for more information.)
  5-26. Attack and reconnaissance aviation units screen forward, to the flanks, or to the rear of a stationary
  main body and to the flanks or to the rear of a moving main body. The ACS is able to provide the maximum
  amount of reaction time and maneuver space when conducting screens, across either a wide frontage or
  operating in-depth with manned-unmanned teams at the ACT or squadron level. Aviation units conduct zone
  reconnaissance forward of a moving body. Aviation units conduct continuous reconnaissance to gain contact
  with the enemy force unless the supported commander directs otherwise.
  5-27. Based on the BCT commander’s security guidance and intent, a screening aviation unit impedes and
  harasses the enemy with organic and supporting fires. Within its capabilities, the unit destroys or repels
  enemy reconnaissance elements without decisively engaging. Upon enemy contact, the aviation unit reports
  the enemy location, maintains contact with the enemy force, and uses its maneuverability and fires to develop
  the situation. The BCT provides priority of fires to the aviation unit so it does not have to rely on its own
  direct fire weapons and risk becoming decisively engaged. Aviation units do not bypass enemy forces without
  the permission or direction of the main body commander.
  5-28. Attack and reconnaissance aviation units maneuver to the enemy’s flanks and rear to locate and exploit
  enemy vulnerabilities and weaknesses and to conduct offensive engagements, such as hasty attack operations.
  However, commanders must weigh the benefit of aviation units conducting an offensive operation against
  the benefit of retaining aviation units in a reconnaissance and security role.
  GENERAL DESCRIPTIONS OF A SCREEN
  5-29. Screens, even for a stationary protected force, are active operations of which stationary, observation
  posts and surveillance assets are only a part of the overall mission. A screen requires employment of mounted
  and dismounted patrols, aerial reconnaissance, and observation posts positioned over extended distances
  in-depth. Inactivity in a stationary screen yields identifiable and exploitable gaps for the threat.
  5-30. The BCT commander provides purpose and guidance to the Cavalry squadron commander. The BCT
  commander states why the screen is important to the BCT mission and how it fits into the scheme of maneuver
  of the BCT mission.
  5-31. Depth provides the BCT commander with more time to react to approaching enemy ground units and
  allows for a reconnaissance handover from one element to another with minimal displacement. Depth
  prevents the threat from easily identifying and penetrating the screen, prevents gaps from occurring when
  observation posts displace, and facilitates the destruction of enemy reconnaissance elements without
  compromising critical observation posts. A unit employs depth by positioning observation posts and other
  information collection assets between the forward line of own troops (FLOT) and the rear boundary of the
  security force.
  5-32. The wider the area to secure, the less the security force can take advantage of increased depth, because
  it has fewer forces to position in-depth. Once the BCT determines the width and depth of the security area,
  the initial screen, and probable avenues of approach, the security force orients on the protected force, area,
  or facility.