Air Information Publications — Page 10, Lesson 20

I want to walk you through the VOLMET broadcast system — this is a key part of the Air Information Publications chapter, and it's something you'll rely on as a professional pilot for in-flight weather updates. Let's start with the title: Meteorological Radio Broadcasts (VOLMETS). VOLMET stands for vol (from the French vol, meaning flight) and met for meteorological — so it's a flight weather broadcast service. These are continuous or scheduled radio transmissions that give you current aerodrome weather reports while you're airborne. Now look at the table structure. Each VOLMET broadcast has seven columns: 1. Call Sign/ID — the name of the broadcast service, like "London VOLMET (Main)". 2. EM — emission mode. You'll see A3E for all of these. A3E is the ICAO designation for amplitude-modulated telephony — basically, ordinary AM voice radio. 3. Frequency MHz — the VHF frequency you tune to receive that broadcast. 4. Operating Hours — all the ones listed here show H24, which means 24-hour continuous operation. 5. Stations — the list of aerodromes whose weather is included in that broadcast. 6. Contents — what information is broadcast and in what order. 7. Remarks — special notes about that particular service. Let me go through each VOLMET service in the table. London VOLMET (Main) — frequency 135.375 MHz, H24 continuous. It broadcasts reports for: Amsterdam, Brussels, Dublin, Glasgow, London Gatwick, London Heathrow, London Stansted, Manchester, and Paris Charles de Gaulle. London VOLMET (South) — frequency 128.600 MHz, H24 continuous. Stations: Birmingham, Bournemouth, Bristol, Cardiff, Jersey, London Luton, Norwich, Southampton, Southend. London VOLMET (North) — frequency 126.600 MHz, H24 continuous. Note 1 says the broadcasting range is extended to cover Southeast England and the English Channel. Stations: Blackpool, East Midlands, Isle of Man, Leeds Bradford, Liverpool, London Gatwick, Manchester, Newcastle, Teesside. Scottish VOLMET — frequency 125.725 MHz, H24 continuous. Stations: Aberdeen/Dyce, Belfast/Aldergrove, Edinburgh, Glasgow, Inverness, London/Heathrow, Prestwick, Stornoway, Sumburgh. Note 2 at the bottom tells you there's also an HF VOLMET broadcast for North Atlantic flights, called Shannon VOLMET, operated by the Republic of Ireland. That one is on HF rather than VHF because it needs to reach aircraft over the ocean. Now let's look at the Contents column in detail — this is the most important part for you operationally. The broadcasts give half-hourly reports, which are METAR — that's the standard aviation routine weather report format. Each report's elements are broadcast in the following order: (a) Surface wind (b) Visibility — or the word CAVOK if conditions are Ceiling And Visibility OK (meaning visibility 10 km or more, no cloud below 5,000 feet, and no significant weather) (c) RVR if applicable — Runway Visual Range, only broadcast when visibility is low (d) Weather — precipitation, obscuration, etc. (e) Cloud — or again CAVOK if applicable (f) Temperature (g) Dewpoint (h) QNH — the altimeter setting to give elevation above mean sea level (i) Recent weather if applicable — weather that occurred in the last hour but has now stopped (j) Windshear if applicable (k) Trend if applicable — the TREND forecast for the next two hours (l) Runway contamination warning if applicable — information about snow, slush, or standing water on the runway Now, a few important operational notes from the Remarks section: Point 3: Non-essential words such as 'surface wind', 'visibility', etc. are not spoken. So you won't hear the announcer say "surface wind" before giving the wind — they just read the numbers and units directly. This keeps the broadcast concise. Point 4: Except for the word 'SNOCLO', the Runway State Group is not broadcast. The Runway State Group is a longer coded message about runway surface conditions. They don't broadcast that whole code — but they do broadcast the single word 'SNOCLO' when needed. Point 5: All broadcasts are in English. And here's the critical definition of 'SNOCLO' : The spoken word 'SNOCLO' will be added to the end of the aerodrome report when that aerodrome is unusable for take-offs and landings due to heavy snow on runways or runway snow clearance. So if you're listening to a VOLMET broadcast and you hear "SNOCLO" at the end of an aerodrome's report, that aerodrome is effectively closed — you cannot plan to land there. That figure shows location indicators, which helps you understand the geographic coverage of these VOLMET services. And gives you an extract from the UK AIP that shows how this information is formally published. So in summary: VOLMET is your in-flight source for half-hourly METAR weather at major aerodromes, broadcast in a fixed order on dedicated VHF frequencies, with all broadcasts in English and non-essential words omitted for brevity. The word 'SNOCLO' is your alert that an aerodrome is closed due to snow.