Remote-Reading Compass Systems: Slaved Correction and Free Mode

022-04-05Pablo Asensio Martínez2026-03-271 min

A Remote Indicating Compass (often called a Gyro-Magnetic Compass) combines a Directional Gyro with a Flux Valve to provide a stable, magnetically-referenced heading without manual resetting.

System Components (FEAT)

The loop works as follows:

  1. Flux Valve: Senses the Earth's magnetic field error.
  2. Error Detector: Compares Flux Valve heading vs. Gyro heading.
  3. Amplifier: Amplifies the error signal.
  4. Torque Motor: Precesses the gyro to align it with magnetic north.

Modes of Operation

  1. Slaved Mode: The normal operating mode. The Flux Valve continuously corrects the Gyro (slowly, to avoid chasing temporary magnetic errors). The gyro is "tied" to Magnetic North.
  2. Free Mode (DG): The slaving is disconnected. The instrument acts like a standard Directional Gyro.
    • Used in Polar Regions (where magnetic field is unreliable/weak).
    • Used if the Flux Valve fails.
    • Requires manual synchronization.

Advantages

  • Eliminates the need for manual resetting (in Slaved mode).
  • Reduces the effect of deviation (Flux valve is in the wingtip/tail).
  • Provides heading data to other systems (Autopilot, RMI, Radar).
Written and reviewed by

Pablo Asensio · 2026-03-27

Aeronautical engineer. Passed the thirteen EASA ATPL(A) theoretical knowledge exams studying from these very notes. Writes and reviews each topic against the Part-FCL Learning Objectives.

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