Definition
An IFR flight plan is a formal request filed with Air Traffic Control to operate an aircraft under Instrument Flight Rules. It includes the aircraft identification, equipment, proposed route, altitude, departure and destination airports, estimated times, fuel on board, and alternate airport. Once filed and activated, it places the flight under positive ATC control and provides separation from other IFR traffic throughout the route.
Plain English
A document a pilot files with air traffic control before flying in clouds or low-visibility conditions. It tells controllers exactly where the pilot intends to go, how, and when, so they can keep the aircraft safely separated from other traffic the entire way.
Context Anchor
You encounter IFR flight plans before an instrument flight when filing or receiving a clearance, and in Air Route Traffic Control Center operations where controllers use the filed information to manage aircraft along routes between airports.
Derivation
IFR stands for Instrument Flight Rules — the set of regulations governing flight by reference to instruments rather than by looking outside. A 'flight plan' in aviation is the filed record of an intended flight. Together, the term describes a flight plan filed under that specific set of rules.
Why Pilots Care
Required to receive ATC separation services and legal clearance when operating in controlled airspace under instrument conditions.
Intuition Check
Do not read “flight plan” as just the pilot’s private plan for the trip. An IFR flight plan is an official filed record used by air traffic control. Also, filing an IFR flight plan is not the same as receiving an IFR clearance; filing asks for IFR handling, while a clearance authorizes it.
Example Sentence 1
The pilot filed an IFR flight plan an hour before departure, listing the route, altitude, and an alternate airport in case of weather at the destination.
Example Sentence 2
After departure, the controller cleared the aircraft to proceed as filed on its IFR flight plan.