A CFII is explaining the Radio Magnetic Indicator (RMI) to an instrument student. Which statement correctly describes how the RMI uses gyroscopic principles to aid navigation?
- AThe RMI combines a gyro-stabilized compass card with a bearing pointer, showing magnetic bearing to a station regardless of aircraft heading
- BThe RMI uses precession alone to point directly at magnetic north at all times
- CThe RMI relies solely on the attitude indicator's gyro to display station bearing
- DThe RMI uses rigidity in space to hold a fixed compass heading that never requires correction
Show answer & explanationAnswer & explanation
Correct answer: A. The RMI combines a gyro-stabilized compass card with a bearing pointer, showing magnetic bearing to a station regardless of aircraft heading
The RMI integrates a gyro-stabilized (slaved) compass card, which continuously displays current magnetic heading, with one or two bearing pointers that indicate the magnetic bearing to a selected NDB or VOR station. Because the compass card rotates with heading changes while the pointer continues indicating the station's bearing, the pilot can read station bearing directly regardless of the aircraft's current heading, unlike a fixed-card ADF indicator.
Why the other options are wrong
- B. Precession is an error source in gyros, not the mechanism by which the RMI points to magnetic north; the RMI uses a slaved gyro compass system instead.
- C. The RMI uses its own dedicated directional gyro/flux valve system, not the attitude indicator's gyro.
- D. Rigidity in space is a gyro property, but the RMI's card is continuously corrected (slaved) to magnetic heading, not held fixed indefinitely.
Radio Magnetic Indicator (RMI)
A combined navigation instrument featuring a gyro-stabilized (slaved) compass card and one or two bearing pointers that display magnetic bearing to a selected NDB or VOR station regardless of aircraft heading.
- Compass card is slaved to a flux valve/gyro system for continuous heading display
- Bearing pointer(s) show magnetic bearing to station, not relative bearing
- Eliminates the need to mentally correct fixed-card ADF readings for heading changes
Memory trick: RMI = a compass card that never lies, always pointing straight at the station