What calls are required for aircraft number 1 and number 2 during an instrument trail departure?

The correct answer focuses on the communication protocols during an instrument trail departure, which are crucial for maintaining safe separation between aircraft in a formation. During this type of departure, aircraft number 1 and number 2 are required to make calls when they reach even numbered thousands of feet, indicating their altitude, as well as when initiating any heading changes. This communication is vital for coordination and situational awareness, as it allows both pilots to monitor each other's progress and compliance with air traffic control instructions.

By calling out at each even thousand feet, both aircraft maintain a structured and clear sequence of their vertical positioning, enabling effective separation and preventing potential altitude conflicts. Similarly, notifying when heading changes occur helps to ensure that both pilots are aligned in their navigation intentions, which is particularly important in a formation context where tight adherence to planned routes and altitudes is necessary.

The other options do not reflect the standard procedures required during such departures. For instance, calling upon takeoff and when initiating turns may not capture the critical altitude reporting aspect, while the suggestion of calling at 5,000 feet and upon landing misses the necessary continuous communication throughout the departure phase. Lastly, arbitrary calls every 10 minutes would not provide the timely updates needed for effective formation flying and would likely lead to