Which of the following is a condition for Gross Navigational Error in oceanic operations?

In oceanic operations, Gross Navigational Error (GNE) refers to significant deviations that can lead to potential safety issues. The correct choice outlines a specific condition that indicates a failure to maintain an accurate flight path that is essential for safety. An estimated time of arrival (ETA) difference of 3 minutes or more can be a critical indication of navigational errors, as it suggests that an aircraft may not be where it is supposed to be within a reasonable time frame. This timing discrepancy can lead to a breakdown in the expected spacing of aircraft, especially in busy air traffic environments over oceans where tracking and separation become more challenging.

The other options, while they may pertain to navigational concerns, do not define Gross Navigational Error as precisely as this specific ETA difference. While a deviation of more than 10 nautical miles from the assigned path is concerning, it does not encompass a temporal element which is critical in assessing the navigation accuracy over long distances where distance measurement may be less reliable than time. Therefore, the condition highlighted by the correct choice is closely associated with maintaining safety and effective air traffic management in oceanic airspace.