Under what circumstances must NRP be retained in the remarks section of the flight plan?

The correct choice refers to the necessity of retaining the Noteworthy Report (NRP) in the remarks section of the flight plan when the aircraft is moved due to weather, traffic, or other tactical reasons. This situation is important because it documents the reason for any changes made to the flight's planned route or altitude. It helps ensure that all parties involved, including air traffic controllers and subsequent responders, have the necessary information to understand the rationale behind the flight's decisions and maneuvers.

Documenting these tactical movements is critical for maintaining situational awareness and ensuring safety in the flight's operational environment. It provides a historical account that can be referenced for any potential inquiries or incidents that occur as a result of the changes in movement. Therefore, capturing this information allows for better coordination and communication among air traffic services and the flight crew.

In contrast, the other situations do not necessitate an NRP to be retained as they involve changes that might not have the same impact on flight safety, operational efficiency, or require further communication or documentation for coordination purposes. For example, significant mechanical issues or a pilot's request for altitude changes may already be communicated through other means or might not require such thorough documentation in the flight plan.