What should number 2 call upon making heading changes?

When number 2 in a formation makes heading changes, it is essential for them to call out those changes to maintain situational awareness within the formation. This communication ensures that all pilots are aware of each other's maneuvers, which is crucial for safe and coordinated flying in close formations.

Calling out heading changes helps the lead aircraft and other formation members adjust accordingly, preventing potential misunderstandings or collisions. It emphasizes the importance of communication between formation members, which is a fundamental aspect of flying in a tight formation where everyone's actions can significantly affect the entire group's safety and integrity.

While fuel status, altitude changes, and speed changes are also important aspects of formation flying, they do not specifically relate to reporting heading changes, which is the core focus of the correct choice in this context.