ADF & RMI Navigation Simulator
Drag the aircraft around the NDB, change your heading, and watch the needles move in real time. See exactly how a fixed-card ADF differs from an RMI — and how relative bearing turns into magnetic bearing to the station.
Top-down map
Tap or drag to move the aircraftAircraft heading
045°Rotate the aircraft and watch the two needles: the fixed-card needle swings (relative bearing changes), while the RMI needle keeps pointing at the same magnetic bearing.
Quick set heading
“Home to the station” turns the nose onto the magnetic bearing, centering the fixed-card needle on 0.
Fixed-card ADF
RB 360°Card fixed · 0 at the nose · needle = relative bearing
RMI
MB 045°Card rotates with heading · needle = magnetic bearing
What the instruments are telling you
Heading
045°
Magnetic bearing to station
045°
Relative bearing
360°
On a heading of 045°, the station is straight ahead, off your nose — at a relative bearing of 360° (about your 12 o’clock). Its magnetic bearing is 045°. The fixed-card ADF shows only the relative bearing, so to turn it into a magnetic bearing you add your heading: 360° + 045° = 045°. The RMI does that math for you — its needle reads 045° straight off the rotating card.
The needle is on the nose, so you are pointed right at the NDB — keep this heading to home to the station.
Relative bearing vs. magnetic bearing
An NDB(non-directional beacon) just transmits — it has no built-in directional information. The aircraft’s ADF (automatic direction finder) receiver simply points its needle at the station. The number you read off that needle depends entirely on the instrument.
Relative bearing (RB) is the angle to the station measured clockwise from the nose. Station dead ahead = 000, off the right wing = 090, off the tail = 180, off the left wing = 270.
Magnetic bearing (MB) is the direction to the station measured from magnetic north — the heading you would fly to go straight to it. The two are tied together by your heading (MH):
MB = RB + MH (mod 360) · RB = MB − MH (mod 360)
Fixed-card ADF
The azimuth card is fixed with 0 at the top (the nose). The needle therefore shows the relative bearingonly. When you turn the aircraft, the needle swings — because the angle from the nose changes even though the station hasn’t moved. To get a magnetic bearing you must add your heading in your head.
RMI
The radio magnetic indicator slaves the compass card to your heading, so your current heading is always under the top index. The same pointer now reads the magnetic bearing to the station directly off the card — no mental math. Turn the aircraft and the card rotates with you; the needle keeps pointing at the same magnetic bearing.
What the FAA tests
- Given a heading and an ADF relative bearing, compute the magnetic bearing to the station (MB = RB + MH).
- Given a heading and a magnetic bearing, work out which way the fixed-card needle points (RB = MB − MH).
- Read an RMI: the tail of the needle is the bearing from the station (the “radial”), the head is the bearing to it.
- Homing (turn toward the needle, keep it on the nose) vs. tracking (apply a wind-correction angle to hold a straight course).
- Recognizing a station passage as the needle swings toward the 180 (tail) position.
Try it: set a heading, then press Home to the station and watch the fixed-card needle snap to 0 while the RMI needle stays put on the magnetic bearing.
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For study and familiarization only — not for navigation or flight planning. Always use approved charts, publications, and certified avionics for actual flight.