Final answer:
At the command of "FALL IN", a flight forms a Line formation, where members stand side by side in a single line, essential for unified movement and response to further commands.
Step-by-step explanation:
At the command of "FALL IN", a flight forms a Line formation. This command is used in military drill and ceremonies to instruct the personnel to assemble in a prescribed formation. In a line formation, the flight stands side by side in a single line, creating a formation that is wide and shallow. Each member of the flight is positioned to ensure proper alignment and spacing, adhering to the specific regulations or commands given by the drill instructor. The objective of forming a line is to present a unified group where commands can be easily seen and heard by all members. This formation is fundamental for parades, reviews, and ceremonial events where the troops are displayed and need to move or act as one.