Definition
An ATC abbreviation used by controllers to indicate handoff or coordination between two IFR aircraft, or between two IFR control facilities. The first 'IFR' refers to the originating aircraft or facility's flight rules status, and the second 'IFR' refers to the receiving aircraft or facility's flight rules status. Used in flight progress strips, coordination messages, and inter-facility communications to confirm that both parties are operating under Instrument Flight Rules.
Plain English
A shorthand controllers use to show that both sides of a handoff or coordination — the aircraft being handed off and the one receiving it, or the two facilities involved — are flying or working under Instrument Flight Rules.
Context Anchor
Seen in air traffic control and separation discussions, especially when describing how one IFR aircraft is handled in relation to another IFR aircraft.
Derivation
Instrument Flight Rules means the set of rules used when a flight is conducted by reference to instruments and air traffic control instructions rather than by outside visual cues alone. The slash in IFR/IFR means “IFR aircraft in relation to IFR aircraft.”
Why Pilots Care
Determines the pilot rating, aircraft equipment, and ATC services required, directly affecting whether a flight can be conducted legally and safely in reduced visibility.
Intuition Check
Do not read IFR/IFR as a route or a clearance by itself. It describes the flight-rule status of both aircraft: IFR aircraft with respect to IFR aircraft.
Example Sentence 1
The strip was annotated IFR/IFR, confirming the handoff was between two instrument-rules flights.
Example Sentence 2
Under IFR the controller issued a heading and altitude to keep the aircraft clear of terrain while it flew through the clouds.