Definition
A flight plan filed with air traffic control (ATC) for a flight conducted under Instrument Flight Rules (IFR), in which the pilot operates the aircraft by reference to cockpit instruments rather than outside visual cues. It includes the proposed route, altitude, departure and destination airports, estimated time en route, fuel on board, and alternate airport, and once activated places the flight under positive ATC control with separation services provided.
Plain English
A flight plan you file before flying in clouds or low-visibility conditions. It tells air traffic control exactly where you intend to go, how high, and by what route, so they can guide you and keep you separated from other aircraft.
Context Anchor
You encounter this during preflight planning, especially when weather, airspace, or the planned operation requires flying under instrument flight rules.
Derivation
“Instrument” originally refers to a tool or device. In aviation, it points to using the aircraft’s cockpit instruments to control and navigate the airplane when outside visual references are not enough. A “flight plan” is the planned information for a flight that is given to the proper aviation service.
Why Pilots Care
Filing the plan gives ATC the information needed to provide separation from other traffic and to issue clearances that keep the flight safe when visual references are unavailable.
Intuition Check
An instrument flight plan is not just any plan that mentions instruments. It means a filed plan for flying under instrument flight rules, with air traffic control involved.
Example Sentence 1
With a low ceiling forecast at the destination, the pilot filed an instrument flight plan and departed under IFR.
Example Sentence 2
The controller activated the instrument flight plan once the aircraft was airborne and the pilot accepted the IFR clearance.