Definition 1 of 2
Definition
An aircraft equipped, certified, and approved to be flown solely by reference to instruments under Instrument Flight Rules (IFR), in conditions where outside visual references may not be available. The aircraft must carry the required instruments, navigation equipment, and certifications, and the pilot must hold a current instrument rating to operate it on an IFR flight plan.
Plain English
An aircraft that has the right instruments and approvals to be flown in cloud or other low-visibility conditions, using only its cockpit instruments to navigate and stay upright.
Context Anchor
Seen in air traffic control, flight plans, weather discussions, and separation rules when distinguishing IFR traffic from VFR traffic.
Derivation
IFR stands for Instrument Flight Rules — the body of regulations governing flight when the pilot cannot rely on looking out the window. An 'IFR aircraft' is therefore one fitted out and approved to fly under those rules.
Why Pilots Care
Enables continued flight and arrival in instrument meteorological conditions while meeting regulatory requirements for certain airspace.
Intuition Check
Do not read “IFR aircraft” as an aircraft that can only fly in clouds. It means an aircraft currently being operated under IFR rules.
Example Sentence 1
The flight school's Cessna 172 is an IFR aircraft, so we can use it for instrument training in actual cloud.
Example Sentence 2
ATC issued a new routing to the IFR aircraft to avoid the active military operations area.