What does a zipper click on the ground indicate?

A zipper click on the ground is an auditory signal used in formation flying, and specifically signifies that the Number 2 aircraft in the formation is ready for VHF check-in early. This call serves as a notification to the lead pilot that the Number 2 is prepared to communicate on the VHF radio, which is often for updating their current status or confirming readiness for the next phase of flight.

Understanding this signal is crucial for maintaining effective communication among formation members, ensuring that all pilots are aware of each other's readiness and situational status. It helps streamline operations and enhances cohesion during flight maneuvers, which is paramount in formation flying. The other choices describe different situations that are not represented by the zipper click, demonstrating the specificity of this communication method.