VOR indicators: CDI, HSI, RMI
VOR indicator: cockpit instrument displaying the signal. Three types: CDI, HSI, RMI.
CDI (course deviation indicator), found in most trainers:
| Part | Function |
|---|---|
| OBS | Omnibearing/course selector |
| CDI needle | Left-right deviation |
| TO/FROM flag | TO or FROM station (see below) |
- Needle centres when aircraft is on the OBS radial, any heading. VOR senses position, not heading (TP 1102).
- Needle centred, flag reading (flying the OBS course):
| Flag | Meaning |
|---|---|
| TO | Course takes you to station |
| FROM | Course takes you away from station |
- Centred and FROM: OBS reading is the radial aircraft is on, measured from station (TP 1102).
HSI (horizontal situation indicator):
- Flux-valve-driven compass card + nav course/radial signal + glideslope.
- Shows aircraft position relative to chosen course.
| HSI flag | Meaning |
|---|---|
| NAV | No reliable signal received |
| HDG | Compass card failed |
RMI (radio magnetic indicator):
- No course selection needed, unlike CDI/HSI.
- Pointer(s) point at selected navaid: VOR, GPS, or ADF.
- Also shows magnetic or DG heading.
Trap: centred needle does not mean tracking the radial. It shows only that aircraft is on the radial now; heading may cross it at any angle.
References
- TP 1102, Instrument Flying: VHF Omni-directional Range (VOR)
- FAA-H-8083-25 PHAK ch.16 (Using the VOR; Course Deviation Indicator; Horizontal Situation Indicator; Radio Magnetic Indicator)