When is a pilot required to file an IFR flight plan?

Filing an IFR flight plan is mandated primarily due to regulations or the need to enter controlled airspace. Under Instrument Flight Rules (IFR), a flight plan is necessary for the safe and efficient management of air traffic, especially in controlled airspace, where specific rules are in place to ensure aircraft separation and safety.

In controlled airspace, pilots must follow established procedures and communicate with air traffic control, which requires an IFR flight plan to be filed. This plan provides essential information about the flight route, altitude, and other pertinent details which help both pilots and air traffic controllers maintain situational awareness.

While other scenarios may involve filing a flight plan, they do not encompass the regulatory requirement as clearly as the necessity to file when operating under IFR or entering controlled airspace. Hence, the correct context for requiring an IFR flight plan centers on adherence to regulations and the structured environment of controlled airspace.