Definition
An aircraft navigation instrument that displays a rotating compass card aligned to magnetic north, with one or two needles that point directly at selected ground-based navigation stations (typically VOR or NDB stations). The pilot reads the magnetic bearing to the station directly off the compass card under the head of the needle.
Plain English
A round cockpit instrument with a moving compass face and one or two needles. Each needle points at a chosen radio navigation station on the ground, so the pilot can see at a glance the magnetic direction to that station.
Context Anchor
Seen in instrument panels and instrument flying discussions, especially when using radio navigation for direction and position awareness.
Derivation
The name describes exactly what the instrument does. 'Radio' because it uses signals from ground radio stations. 'Magnetic' because the compass card is slaved to magnetic north. 'Indicator' because it shows the result on a dial. Knowing this makes the function easy to remember: a radio-driven, magnetic-referenced pointer.
Why Pilots Care
It combines heading and bearing information on one instrument so the pilot can orient the aircraft to a station without separate calculations.
Grounding Statement
As the airplane turns, the compass card shows the new magnetic heading while the pointer continues to show the direction to the selected radio navigation source.
Intuition Check
“Magnetic” does not mean the instrument is simply using a magnet like a household compass. Here it means the heading and bearing information are shown relative to magnetic north.
Example Sentence 1
She tuned the VOR and watched the RMI needle swing around to point directly at the station.
Example Sentence 2
As the aircraft passed the station the pointer on the Radio Magnetic Indicator swung around indicating the change in relative bearing.