Learn what a radio magnetic indicator shows, how to read ADF/VOR bearings, track a station, fix your position and avoid common errors.
In real-world aviation and flight simulation, a radio magnetic indicator (RMI) combines a rotating magnetic-heading card with one or two pointers showing the bearing to a selected NDB or VOR station. Tune and identify the station, select the pointer source, then read the pointer head against the card as the magnetic bearing to the station.
What does an RMI show?
An RMI shows aircraft magnetic heading and the magnetic bearing to a radio-navigation station on the same instrument. The heading under the top index is the aircraft’s heading, while each arrowhead points towards its selected station.
The pointer tail gives the reciprocal bearing from the station. For example, if the arrowhead reads 045°, the station lies on a magnetic bearing of 045° from the aircraft, and the tail at 225° gives the approximate bearing from the station to the aircraft. If the aircraft is heading 090°, that station is 45° to the left of the nose.
Most traditional RMIs have two differently shaped pointers, with selectors allowing each pointer to receive ADF or VOR information. The exact selector labels, needle shapes and available sources vary by aircraft. DME readouts sometimes fitted beside an RMI are an additional feature, not part of the basic RMI function.
How do you read and use an RMI?
- Check the heading card. Confirm that the heading at the top agrees reasonably with the aircraft’s other heading instruments. A failed or unsynchronised heading source makes the indicated magnetic bearing unreliable.
- Tune the station. Set the required NDB frequency on the ADF receiver or the VOR frequency on the navigation receiver.
- Identify the signal. Listen for the published Morse identifier where the aircraft and simulator model it. Needle movement alone does not prove that the correct station has been received.
- Select the pointer source. Set the relevant pointer to ADF, VOR or the source label used by that aircraft. Do not assume that pointer one always uses VOR and pointer two always uses ADF.
- Read the arrowhead. The number beneath the pointer head is the magnetic bearing to the station. The tail supplies the reciprocal bearing from it.
- Choose homing or tracking. Turn towards the pointer for a simple direct path, or intercept and hold a planned bearing when following a defined route.
The OBS course selected on a conventional VOR indicator generally does not control a pure RMI pointer. The RMI reports where the station lies rather than displaying deviation from the course selected with the OBS. Our practical VOR and NDB tuning and tracking procedure covers the receiver work behind the indication.
How do you track a station with an RMI?
For basic homing, turn until the pointer head reaches the 12 o’clock position and keep it there. This continually points the aircraft’s nose at the station, but wind will produce a curved ground track rather than a straight one.
Tracking an inbound bearing
To follow a defined inbound track, intercept the required magnetic bearing and apply a wind-correction angle. If the planned inbound bearing is 045°, the pointer head should remain over 045° on the rotating card even though the aircraft may need to fly a heading several degrees either side of 045°.
If the pointer moves away from the desired bearing, correct back towards the route and adjust the wind correction. The mistake we see most often is chasing the pointer under the top index, which is homing rather than tracking.
Tracking outbound and fixing position
For an outbound route, use the pointer tail as the bearing from the station. After passing overhead, establish the outbound heading and let the pointer settle before making corrections; it can swing rapidly during station passage.
Two pointers tuned to different stations can provide a cross-bearing fix. Plot each bearing from its station using the pointer tails, and the lines intersect near the aircraft’s position. One bearing plus distance can also produce a useful fix; our guide to combining an NDB bearing with DME distance explains that method.
Is an RMI the same as an ADF or HSI?
An RMI is a display instrument, while ADF and VOR are navigation sources. An HSI instead concentrates on a selected course and lateral deviation, although modern electronic HSIs may add RMI-style bearing pointers.
| Instrument | Primary indication | Best used for |
|---|---|---|
| Fixed-card ADF indicator | Relative bearing from the aircraft’s nose | Basic direction finding to an NDB |
| RMI | Magnetic heading and direct bearing to a station | Homing, bearing tracking and position fixes |
| CDI or HSI | Deviation from a selected course | Accurate route and approach tracking |
| Electronic bearing pointer | RMI-style bearing over a navigation display | Monitoring VOR, ADF or supported waypoint sources |
Glass-cockpit bearing pointers use the same basic interpretation even when there is no separate mechanical RMI. A more specialised example is our worked Airbus A320 DDRMI explanation, which covers its dual pointers and associated distance displays.
Why is the RMI needle wrong or not moving?
An RMI needle that is parked, frozen or pointing unexpectedly usually indicates a receiver, source-selection, signal or heading-reference problem. Check these causes before attempting to follow it:
- Wrong source or frequency: confirm the active frequency and the selector for that specific pointer.
- No valid reception: VOR is line-of-sight and both VOR and NDB have finite usable range. Terrain, altitude and facility status affect reception.
- Missing identification: another station or interference may produce a believable but incorrect indication.
- Heading-card error: a failed compass system or unsynchronised heading reference corrupts the magnetic bearing displayed against the card.
- NDB propagation errors: thunderstorms, coastal refraction, night effects, terrain and aircraft structure can disturb ADF bearings. The effect known as NDB quadrantal error and its characteristic bearing distortion is one specific example.
- Station passage: expect rapid pointer movement close to or directly above the transmitter. Do not chase the needle through the overhead.
- Simulator simplification: aircraft differ in how they model reception limits, failure flags, electrical buses and no-signal needle parking. Verify the aircraft’s own source selectors rather than assuming every RMI behaves identically.
An RMI tells you where the selected station is; it does not by itself show obstacle clearance, route approval, glideslope information or deviation from a selected course. Use it with the chart, flight plan and the aircraft’s other navigation instruments.