Which statement best describes a Phase Line?

• A. A designated phase line where responsibility transitions from one unit to another
• B. A line that serves as a boundary between units
• C. A point where air traffic is controlled
• D. A fixed supply point

Answer: (A)

Phase lines are control measures that mark where command authority shifts from one unit to another as the operation advances. The statement describing a designated phase line where responsibility transitions from one unit to another is the best fit because it directly captures the purpose of a phase line: signaling the handover of control as phases of the operation change. The other ideas describe general boundaries, air traffic control points, or supply points, which are not what a phase line is used for.