When must the NPR be entered in the remarks section of a flight plan?

The inclusion of the Notice of Proposed Rulemaking (NPR) in the remarks section of a flight plan is essential when prior coordination has been completed with the Air Traffic Control System Command Center (ATCSCC) or through international Notice of Proposed Rule (NPR) procedures. This coordination indicates that the flight is operating within specific guidelines that may modify standard procedures due to operational needs, traffic management initiatives, or safety concerns.

By documenting this in the remarks, air traffic controllers are made aware of the flight's context, allowing for better situational awareness and management of airspace. This practice ensures effective communication between the pilot and air traffic management, facilitating the safe and efficient flow of air traffic.

In contrast, options related to filing errors, VFR conditions, or operating outside controlled airspace do not specifically require the entry of an NPR in the remarks section. Each of those cases involves different considerations that do not necessitate the same level of coordination or communication as required under the circumstances laid out in the correct answer.