What is one requirement for pilots to file an IFR flight plan?

Filing an IFR (Instrument Flight Rules) flight plan requires pilots to receive clearance from air traffic control (ATC). This is a critical step in ensuring that the aircraft can safely operate in controlled airspace and that ATC can manage air traffic efficiently. Clearance serves as a formal permission to depart under IFR, ensuring that all safety protocols and traffic separation requirements are adhered to. Once cleared, pilots are expected to follow the assigned routing and altitudes as directed by ATC, thus maintaining safety and orderly flow of air traffic.

The other choices do not meet the mandatory requirements for filing an IFR flight plan. Passenger approval, visual flight rules adherence, and submitting a flight itinerary to the FAA do not constitute necessary steps in the IFR clearance process. These factors may be relevant in different contexts, but they do not replace the need for official clearance from air traffic control.