Under what condition can advice or instructions be issued when providing preventive control?

When providing preventive control, advice or instructions are issued primarily when the situation requires corrective action. This means that if there is a potential issue or a risk that could lead to a conflict or an unsafe situation, the air traffic controller will provide guidance to mitigate that risk.

By focusing on situations that necessitate intervention, controllers can help maintain safety and efficiency in air traffic management. Preventive control aims to proactively address situations before they escalate into more serious problems, making the issuance of advice or instructions during these critical times essential for effective air traffic control strategies.

The other conditions listed—only on request, when traffic is light, and under normal operations—do not inherently dictate a need for intervention or the provision of instructions. Instead, preventive control is about taking action when it’s clear that doing so will improve safety and operational flow.