Radio Navigation
Principles of radio aids used in IFR navigation.
Radio navigation relies on ground-based aids that emit radio signals captured and interpreted by onboard instruments. It is the foundation of conventional IFR navigation.
The three main aids
| Aid | Frequency | Information provided | Cockpit instrument |
|---|---|---|---|
| VOR | 108.0-117.95 MHz | Radial (magnetic azimuth) | Course Deviation Indicator (CDI) |
| NDB | 190-535 kHz | Direction to the station | RMI (ADF needle) |
| DME | paired with VOR | Slant range in NM | DME display |
Common principles
Bearings and radials
Any radio signal can be used to determine a bearing — the angle between the station and the aircraft:
- QDM: Magnetic heading to fly towards the station
- QDR: Magnetic bearing from the station (= QDM +/- 180°)
- Radial: Synonym for QDR when referring to a VOR
Reading the RMI
On the RMI, the reading is direct:
- Needle head = QDM (heading to reach the station)
- Needle tail = QDR (bearing from the station)
Station passage
Station passage (or overhead passage) is detected when:
- The RMI needle swings 180° (the station goes from ahead to behind)
- The TO/FROM flag flips on the CDI
In HOLD: Press Space (TOP button) to mark station passage. The precise timing of the TOP is a scoring criterion.