An aircraft on a VFR flight plan is first considered ________ 30 minutes after its ETA.

The correct answer is "overdue." When an aircraft is operating under a Visual Flight Rules (VFR) flight plan, it is expected to arrive at its destination by a specified estimated time of arrival (ETA). If the aircraft has not arrived within 30 minutes after this ETA, it is categorized as overdue.

The term "overdue" specifically indicates that the aircraft has not reported its arrival as anticipated, which prompts search and concern for its safety. This is a standard protocol to help ensure that timely action can be taken in case of potential emergencies, such as navigation errors or mechanical failures.

The distinction of being "overdue" is significant in operational contexts, as it triggers a response from air traffic control and search and rescue teams. It represents a point in time that triggers concern but does not yet assume an emergency situation. Other terms, while they might seem similar, have specific meanings related to different circumstances.