What indicates that the formation can switch to departure frequency?

The correct choice highlights that both aircraft must be airborne to switch to departure frequency. This is critical because coordinating frequency changes among multiple aircraft ensures that communication remains intact and operational safety is maintained. If both the lead and wingman aircraft are in the air, they can effectively communicate any necessary updates or changes with each other and air traffic control, reducing the risk of miscommunication or separation issues.

When both aircraft are airborne, they can monitor the departure frequency together, which allows them to maintain their formation and ensures they are both on the same page regarding flight instructions from air traffic control. This operation reflects standard practice during military and formation flying, where maintaining situational awareness and communication is vital to safe flight operations.

In cases where only the lead aircraft is in the air, or if only wingman clearance is provided, there could be potential lapses in communication or coordination. If both aircraft have landed, it is already too late for them to switch to departure frequency, emphasizing the importance of the requirement for both to be airborne before making the frequency transition.