VOR receiver accuracy check
A VOR receiver accuracy check proves the instrument, not the station, is trustworthy before use.
Station standard (facility figure, not a receiver check tolerance; TC AIM COM 4.5(d)):
| Radial | Course alignment accuracy |
|---|---|
| Published | ±3° |
| Unpublished | No standard; may be affected by siting difficulties |
VOT check (most large airports have a VOR test frequency):
| OBS set | Sense indicator | CDI |
|---|---|---|
| 360° | FROM | centred |
| 180° | TO | centred |
- Up to ±4° OBS error at either setting acceptable for IFR.
- OBS 10° either side of centre: CDI full deflection (proves needle sensitivity).
Other checks:
| Check | Method | Tolerance |
|---|---|---|
| Ground checkpoint (no VOT) | Tune published checkpoint, compare indicated radial to known | ±4° |
| Airborne checkpoint (no VOT) | Same | ±6° |
| Dual receiver | Both tuned to same station, indicated bearings must agree | ±4° |
Use of results:
- No error limit regulated for VFR flight.
- Do not fly on a receiver suspected inaccurate.
- Navigating: set OBS to required track, never offset by measured error (error not guaranteed the same on every radial). VOT test itself uses OBS 360° and 180°.
Trap: dialing a 3° VOT error into every course flown (error varies by radial; a receiver failing the check is unreliable, not correctable); applying the station ±3° to an unpublished radial.
References
- TP 1102, Radio Navigation: Very High Frequency Omni-directional Range (VOT)
- PHAK ch.16, VOR (accuracy checks)
- TC AIM COM 4.5(d)