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RMI and HSI Navigation

After this briefing, the student should have a reasonable understanding of navigating with the Radio Magnetic Indicator (RMI) and Horizontal Situation Indicator (HSI). The lesson will be complete when they can apply that knowledge to a DME arc using a desktop flight simulator.


  • RMI
  • HSI
  • Navigating and tracking
  • Arcing


  • model aircraft

  • whiteboard and markers
  • ASA’s Pilot’s Manual 3: Instrument Flying, chapter 12b and 12c
  • Instrument Flying Handbook
  • laptop with internet access
  • Instructor actions

    • Describe the basics of the RMI and HSI
      • how it functions
      • what aircraft it would be found in
    • Explain use of the RMI using Instrument Flying chapter 12c
    • Explain use of the HSI using IF chapter
    • Demonstrate tracking and arcing with Tim’s simulator
    • Evaluate student’s knowledge with various ‘random’ scenarios in Tim’s simulator

    Student actions

    • Prepare by spending a half hour with Tim’s simulator
    • Maintain active involvement by responding to questions and taking notes
    • Guide the instructor through the intercepting and tracking of several simulator scenarios

    Completion standards

    The lesson will be complete when the student can demonstrate an understanding of the techniques required to smoothly and accurately intercept, track, and arc using an RMI with minimal instructor guidance.

    Teaching outline

    • What is an RMI?
      • RBI overlaid on a heading indicator
      • it also allows us to tune a VOR and use it like an NDB
    • Relatively common equipment in more advanced aircraft
      • newer cockpits generally incorporate an RMI
      • included in many digital HSIs and most glass PFD setups

    Design and operation

    • Essentially an ADF with a slaved compass card
      • flux gate compass doesn’t require constant pilot attention
      • if we tune a VOR, it works just like another ADF and constantly points to the station
    • Graphic representation of where we are relative to a station
      • head (arrow) shows the magnetic bearing TO the ground station
      • tail shows our current bearing FROM
      • if we’re tuning a VOR, it shows to and from radials
    • Intercepting and tracking illustrated IF 260
    • Intercepting and arcing illustrated IF 568
      • much like arcing with a VOR, but we wait until the head is 10° behind, then turn 20°
      • we can up our precision by waiting 5°, turning 10°
    • Following explanation, demonstrate tracking and arcing with Tim’s simulator


    • What is an HSI?
      • all in one instrument that gives you: heading, course selector, glide slope and to/from.
      • makes instrument scan easier and faster by getting more information from one instrument.
    • Frequency and bearing set just like a VOR or ILS
    • Information is interpreted like the VOR or ILS.

    HSI display

    • terminology
    • operation

    Components and operation

    • Flux gate compass, mounted remotely
      • Usually on a wingtip – as far from equipment as possible
      • Measures amount of magnetic flux through three coils
      • As the aircraft rotates, the current through each coil varies
    • HSI
      • Compass card and directional gyro
      • Slaved to the flux gate, automatically updates
      • Can be overridden in manual mode and then suffers from precession errors just like a normal heading indicator
    • CDI
      • Functions like a normal fixed CDI
      • OBS knob selects the radial by turning the actual course pointer and CDI needle
    • Glide slope
      • Glide slope bars are on the sides of the instrument, rather than a needle


    • Arcing is made easy – we visually cross the radials
    • Provides us with constant position information
    • We speed up our scan by combining heading with VLOC
    • ILS and localizer backcourse
      • Set HSI to the “front course” heading; the HSI will read correctly
      • Unlike normal CDI, we do not get reverse sensing provided front course is set