AWOS and LWIS voice broadcasts
VGSS (voice generator sub-system): voice of an AWOS or LWIS ground station. Reads data aloud on VHF or telephone once a minute (TC AIM MET 8.4.3(h), MET 8.5).
Status:
- Extra, up-to-the-minute source. NOT an official observation, METAR or SPECI (TC AIM RAC 4.5.1).
- Wind and altimeter data may be used to fly an instrument approach (TC AIM RAC 4.5.1).
- Human METAR/SPECI takes priority; VGSS normally off during it.
- Missing data reads "MISSING" (TC AIM MET 8.4.3(h), MET 8.5).
Wind direction (TC AIM MET 8.4.4, Table 8.3):
| AWOS location | Broadcast direction |
|---|---|
| Southern Domestic Airspace | Magnetic |
| Elsewhere | True |
- LWIS reports true; only VGSS converts to magnetic, within SDA (TC AIM MET 1.2.5.2).
Range: VGSS receivable on VHF to 75 NM from site at 10 000 ft AGL (TC AIM MET 8.5).
Variable weather: compare several broadcasts; ones only a few minutes apart can differ significantly (TC AIM MET 8.5).
Trap: treating AWOS/LWIS broadcast as official observation, METAR or SPECI.
References
- TC AIM MET 1.2.5.2
- TC AIM MET 8.4.3(h)
- TC AIM MET 8.4.4
- TC AIM MET 8.5
- TC AIM RAC 4.5.1