What is an aerodrome weather station?

It is the system that collects readings from the weather sensors at the aerodrome, checks and averages them, and turns them into reports. The usual sensors measure wind, visibility and RVR, cloud base, air temperature and dew point, pressure and present weather such as rain, snow or fog. Automated systems of this kind are often called AWOS.

Normally a wind sensor on a mast, visibility and RVR sensors beside the runway, a ceilometer for cloud base, a shielded temperature and humidity probe, a barometer for pressure and a present-weather sensor. The aerodrome and the meteorological authority decide which sensors are needed and where. The earlier entries in this division cover the wind, visibility, ceilometer, RVR and temperature sensors one by one.

Local routine and special reports for ATC, METAR and SPECI messages for the wider network, and data for displays, ATIS and other users. The station averages the readings over set periods, applies range and consistency checks and flags missing or doubtful values. Pressure is reported in hectopascals as QNH (in METAR and local reports) and QFE (in local reports where required), taken from a barometer that is usually indoors with a static pressure inlet.

The sensors are spread over the aerodrome where each one is representative: wind and visibility sensors near the runway, the cloud sensor on the approach path, the temperature probe in an open enclosure and the barometer indoors. Cables run back to the station, normally in the ATC or meteorological office. The meteorological authority decides the positions, and masts in the protected areas must be frangible.

It is a separate meteorological system and not part of the series circuit, but it shares the airfield, power, ducts and earthing. Its RVR and visibility values are used with the lighting intensity step, and visibility and ceiling readings trigger low-visibility procedures. Interfaces to the airfield lighting control and monitoring system vary by aerodrome, so follow the approved design.

The station should raise an alarm and mark the value as missing or doubtful rather than report a stale number. Pilots and controllers act on these values, so a stuck or frozen reading can be more dangerous than none. Faults are fixed under the aerodrome's procedures, and ATC and the meteorological authority are told before a sensor is taken out of service.

Sensors near the runway need the permit-to-work and aircraft-movement controls, and masts need safe working at height. Power, surge protection and earthing must be isolated and proven before work. Because the readings feed approach minima and reports, always tell ATC and the meteorological authority before any sensor, processor or link is taken out of service or changed.