Who is responsible for asking if a VFR aircraft requesting IFR clearance has a flight plan on file?

The responsibility for asking if a VFR (Visual Flight Rules) aircraft requesting an IFR (Instrument Flight Rules) clearance has a flight plan on file primarily lies with the Radar Controller. This is because Radar Controllers are tasked with managing aircraft in controlled airspace and ensuring that all necessary flight plans are accounted for before granting IFR clearances.

When a VFR aircraft requests an IFR clearance, it's crucial for the Radar Controller to ensure that there is an active flight plan, as it is a necessary prerequisite for the IFR service to be provided. If there was no flight plan on file, the Radar Controller would need to direct the pilot to file one before proceeding. This process helps maintain safe and organized air traffic operations and ensures that all required documentation for the flight is completed. The roles of Ground Controllers, Flight Service Stations, and Air Traffic Supervisors do involve aspects of coordination and communication, but they are not primarily responsible for verifying flight plans in this specific context.