RMI and VOR Usage

RMI Explained and VOR Integration

The RMI combines a slaved compass card with one or more needles that can be switched to display bearings from VOR or ADF (NDB) stations. When tuned to a VOR, the needle's head points to the magnetic bearing TO the station (QDM), and the tail indicates the radial FROM the station (QDR). This direct presentation means the pilot can read their current VOR radial at a glance by looking at the tail of the needle.

How to Use RMI with VOR

• Set the RMI to VOR mode and select the desired VOR frequency.
• The compass card automatically aligns with the aircraft's magnetic heading.
• The needle head gives the magnetic bearing to the VOR; the tail shows the radial (bearing from the station) you are currently on.
• To track to a VOR, turn the aircraft to keep the needle head at the top (12 o'clock) position.

RMI vs CDI and HSI

• The RMI provides continuous bearing information but does not show lateral deviation from a selected course (unlike the CDI or HSI).
• The CDI (Course Deviation Indicator) and HSI (Horizontal Situation Indicator) allow course selection and give left/right guidance for intercepting or maintaining a radial.
• RMIs excel at quick orientation and situational awareness, while CDIs/HSIs are better for precise tracking.

Types of VOR Stations

• Conventional VOR (CVOR): Uses a rotating antenna for signal emission.
• Doppler VOR (DVOR): Employs fixed antennas and the Doppler effect for improved accuracy.
• En-route VOR: Used for airway navigation, typically spaced up to 80 NM apart.
• Terminal VOR (TVOR): Lower power, shorter range, supports approach/departure at airports.
• Test VOR (VOT): Used for equipment checks, emits a constant phase difference.

VOR Identification and Monitoring

• Every VOR transmits a Morse-code identifier, sometimes with additional voice or data.
• Stations have automatic ground monitoring; if out of tolerance, identification and navigation signals are removed or transmission ceases for safety.

RMI Indications in Practice

• The RMI is especially useful for cross-checking position with multiple VORs or when flying direct routes.
• For exam questions, always read the radial from the tail of the needle and remember the compass card shows magnetic heading, so ignore magnetic variation unless specifically asked otherwise.