When is an IFR flight plan required to be filed?

An IFR flight plan is required to be filed when operating under Instrument Flight Rules (IFR) in controlled airspace. This is important because an IFR flight plan provides essential information for air traffic control (ATC) to maintain safe separation between aircraft and to manage air traffic effectively.

When flying under IFR, pilots are operating in conditions where visual references to the ground or other aircraft may not be sufficient to navigate safely, such as in clouds or reduced visibility. The IFR flight plan lays out the proposed route, altitude, and other critical information, allowing ATC to issue clearances and ensure that traffic is managed appropriately along that route.

Furthermore, in controlled airspace, the requirement for an IFR flight plan is part of ensuring safety and efficiency. Controlled airspace includes sectors where air traffic services are provided, and the filing of an IFR flight plan allows for adherence to specific air traffic regulations and procedures.

In contrast, flying under visual flight rules (VFR), in uncontrolled airspace, or above 10,000 feet does not automatically necessitate an IFR flight plan, making those options incorrect. The requirement is explicitly tied to operating under IFR in controlled airspace.