NDB characteristics
NDB: low/medium frequency, flown with the ADF.
| Item | Frequency |
|---|---|
| NDB band | 190-415 kHz and 510-535 kHz |
| ADF receiver tuning | 190-1,750 kHz (NDBs plus commercial broadcast stations) |
- Also used as ILS marker beacons and for NDB non-precision approaches.
(TC AIM COM 4.6; TP 1102 Instrument Flying: Automatic Direction-Finder)
Identification:
- NDB: continuous Morse identifier (PHAK ch.16), usually three letters (TC AIM COM 4.6(a) allows two or three).
- Commercial broadcast station used for ADF: no such code. Before trusting bearings:
- Confirm by listening to station ID.
- Check no back-up antenna site is in use.
NDB station classes, by power output (TC AIM COM 4.6(b)):
| Class | Power |
|---|---|
| L | under 50 W |
| M | 50 W to under 2,000 W |
| H | 2,000 W or more |
Accuracy, flight checked to at least (TC AIM COM 4.6(c)):
| Approach | En route |
|---|---|
| ±5° | ±10° |
Errors (can be much larger than the flight-check figures):
- Night effect
- Terrain effect: reflected signals from high terrain
- Thunderstorm interference (electrical storms): needle swings toward the storm
- Propagation disturbance at sunrise/sunset
- Shoreline refraction when crossing at under 30°
Trap: treating the ADF needle as steady in a thunderstorm. It swings toward the storm.
References
- TC AIM COM 4.6
- TP 1102 Instrument Flying: Automatic Direction-Finder
- TC AIM COM 4.6(b) (NDB classification)
- TC AIM COM 4.6(c)