Meteorological Information for Aircraft in Flight — Page 541, Lesson 523

I want to walk you through two key sources of in-flight meteorological information: VOLMET broadcasts and the Automatic Terminal Information Service, or ATIS. Let's start with VOLMET. The Shannon VOLMET is a vital source of weather information for North Atlantic flight routes. Now, VOLMET itself is a type of broadcast — the name comes from the French vol for flight and météo for weather. The types of VOLMETs shown contain the same information as the VOLMETs for mainland United Kingdom, although they are more likely also to contain additional weather forecast details, such as SIGMETs for en route weather. A SIGMET is a message concerning significant meteorological phenomena that could affect aircraft safety — things like severe turbulence, icing, or thunderstorms along your route. VOLMET transmissions are designed to be simple and easily understood, so that fast, efficient weather briefing can be obtained by pilots, in flight. That's the whole point: you're airborne, you need the information quickly, and the broadcast is structured to give it to you clearly without complex decoding. During preflight planning, note down the VOLMET frequencies for the areas that you will be flying in. Then, en route, you can listen to broadcasts for aerodromes in the vicinity of your destination, as well as for alternate aerodromes. So you're not just checking your destination — you're also checking where you might divert to if needed. Access to VOLMET broadcasts enables the pilot to confirm that weather conditions at his destination airfield are favourable. If a diversion becomes necessary, the current suitability of the planned diversion airfield can also be rapidly determined. That's a critical operational benefit: you don't have to wait for a controller to relay the weather; you hear it directly from the broadcast. Now let's move to ATIS — the Automatic Terminal Information Service. ATIS is a continuous broadcast of current aerodrome weather and other aerodrome information. The word "continuous" is important — it repeats the same message on a loop, so you can tune in at any time and get the latest report. The purpose of the ATIS is to improve controller effectiveness and to reduce congestion on busy ground, tower and approach frequencies by automatically transmitting on a discrete VHF radio frequency. Instead of every pilot calling the controller to ask for the weather, you listen to the ATIS broadcast on its own dedicated frequency. That frees up the controller to handle clearances and traffic. Pilots departing from or arriving at aerodromes which offer ATIS are encouraged to listen to the ATIS broadcast and to notify air traffic control, on initial contact, that they have received the ATIS broadcast, by passing the phonetic alphabet code letter by which all ATIS broadcasts are identified. Every ATIS broadcast is identified by a letter of the phonetic alphabet — Alpha, Bravo, Charlie, and so on. When you first call the controller, you say something like "Information Alpha received" so they know you have the current weather and runway information. At some aerodromes there will be a separate ATIS broadcast for departure and arrival. So if you're departing, you might listen to the departure ATIS, and if you're arriving, you listen to the arrival ATIS — each with information relevant to that phase of flight. Finally, in order to free up air traffic VHF communication frequencies, some aerodromes transmit the ATIS information on the voice channel of a VOR beacon located at the aerodrome. A VOR is a VHF omnidirectional range navigation aid, and it has a voice channel built in. By putting the ATIS on that VOR voice channel, you don't need a separate frequency just for the weather broadcast — it uses the navigation aid's existing capability. So to summarise: VOLMET gives you in-flight weather for aerodromes and en-route conditions via simple, easily understood broadcasts, and you should note the frequencies during preflight planning. ATIS gives you a continuous, automated broadcast of current aerodrome weather and information on a discrete VHF frequency, identified by a phonetic code letter, and you tell the controller which letter you've received. Both are designed to reduce frequency congestion and give you the information you need efficiently.