Under what condition should DME/ATD procedures be used?

The correct condition for using DME/ATD procedures is when direct communication is established. This is essential because DME (Distance Measuring Equipment) and ATD (Automated Terminal Information Services) rely on effective communication between the pilot and air traffic control to ensure that the data provided is accurate and relevant for navigation and approach procedures. Direct communication allows controllers to provide timely instructions and updates to pilots, helping them to effectively utilize the information obtained from DME data.

In scenarios without direct communication, the reliability of instructions could be compromised, leading to potential safety risks. Proper coordination and clear communication between pilots and controllers are crucial for successful navigation and operational safety while using DME/ATD procedures.

While the other choices present various contexts where DME/ATD procedures might seem applicable, they do not encompass the fundamental requirement of effective communication between the pilot and air traffic control, which is paramount for the successful use of these procedures.