ADF/NDB terms
ADF needle: points at tuned NDB. Reads bearings on fixed-card dial (0 at nose, 180 at tail).
| Term | Meaning |
|---|---|
| Relative bearing | Clockwise angle from nose to beacon. ADF needle shows it directly |
| Magnetic bearing to beacon | Relative bearing + magnetic heading. Subtract 360 degrees if over 360 |
| Reciprocal bearing | Bearing ± 180 degrees. Plotting fixes: beacon-to-aircraft bearing is reciprocal of aircraft-to-beacon bearing |
| Position line | Line on chart from one bearing taken on a beacon, or from a VOR radial |
| Fix | Where 2 or more position lines intersect. Lines from different NDBs, or from an NDB and a VOR |
| LF/MF airway | Charted track joining two NDBs, based at 2,200 ft AGL. Convergence and variation: tracks at each end not always exact reciprocals |
| LF/MF airway and air route system | Based on NDBs (TC AIM COM 4.6) |
Trap: adding heading and relative bearing without the 360-degree wraparound check; mixing up a bearing with its reciprocal when plotting a fix.
References
- TP 1102 Instrument Flying: Automatic Direction-Finder, Terms and Definitions
- TP 1102 Instrument Flying: Flying LF/MF Airways
- TP 1102 Instrument Flying: Determining a Fix (ADF)
- TC AIM COM 4.6 (NDB airway and air route basis)