Radio Navigation
Radio navigation glossary
This glossary defines the radio navigation terms that most often cause confusion in instrument training: what each one means, why it matters in the air, and a worked micro-example. Each entry links to the article that covers the associated technique in full. Definitions answer what a term IS; the articles answer how to fly it.
Articles in this cluster
Radial vs courseA radial is always measured outbound from a VOR. A course is the track you select on the OBS. They differ by 180 degrees whenever you track inbound.QDM and QDRQDM is the magnetic bearing TO a station; QDR is the magnetic bearing FROM it. They are reciprocals, and the Q-codes survive in IFR training language.TO/FROM flagThe TO/FROM flag reports which side of the VOR your selected course would take you, not which way you are flying. It is a sense check, not a direction.Cone of confusionThe cone of confusion is the region above a VOR where no usable azimuth signal exists, so the needle wanders and the flag drops until you pass the station.Slant rangeDME measures the straight-line distance to the beacon, not the distance over the ground, so the reading is always slightly high and worst overhead.HSI, CDI and RMIA CDI shows displacement from a selected course, an RMI points at the station, and an HSI combines a heading card with a CDI in one instrument.Drift angleDrift angle is the difference between the heading you are pointing and the track you are making good. It is what the wind does to you, measured in degrees.Relative bearingRelative bearing is the angle from the nose to the station, measured clockwise. Add it to magnetic heading to get the magnetic bearing to the beacon.