What must be done when the NO APPR annunciator is displayed on the PFD?

When the NO APPR annunciator is displayed on the Primary Flight Display (PFD), it indicates that the Flight Management System (FMS) is not set up to provide guidance for an instrument approach. This is a crucial alert because relying on an approach that the FMS is unable to support can lead to serious navigational errors during critical phases of flight, especially during approach and landing.

As a result, the correct action is to prohibit the use of FMS guidance for instrument approaches. Pilots must recognize that the system is indicating a limitation, meaning they must switch to other navigation methods that are reliable and appropriate for the approach being conducted. This ensures the safety and effectiveness of the flight operation, enabling pilots to revert to manual navigation techniques or alternate means of navigational support.

While other options might seem reasonable, they do not directly address the critical nature of the NO APPR indication or imply a less cautious approach regarding navigational safety. Therefore, adhering strictly to the guidance prohibits reliance on the FMS under such circumstances.