Air Traffic Services — Page 282, Lesson 365

I want to walk you through the meteorological and automatic information services that sit inside Air Traffic Services. We’re starting with SIGMET and AIRMET, then moving into OFIS and ATIS. First, SIGMET. According to Annex 11, AIRMET is defined as: ‘Information issued by a meteorological watch office concerning the occurrence or expected occurrence of specified en route weather phenomena which may affect the safety of aircraft operations.’ So AIRMET is a weather advisory, issued by a meteorological watch office, about specified en route weather phenomena — things like turbulence, icing, or thunderstorms — that may affect the safety of aircraft operations. The key word is "may" — it’s a warning of potential hazard along your route. Now OFIS. OFIS is broadcast in three specific areas: HF OFIS, VHF OFIS, and ATIS. Both HF OFIS and VHF OFIS broadcast VOLMET information — that’s METAR, SIGMET, and TAF — for specific aerodromes, or groups of aerodromes, in accordance with a schedule. So VOLMET is the package of weather reports: METAR is the routine aerodrome weather report, SIGMET is the significant weather warning, and TAF is the terminal aerodrome forecast. OFIS broadcasts these on a fixed schedule for designated airports. Let me show you the VHF OFIS Volmet coverage in the London, Scottish, and Shannon FIRs. Look at Figure 15.1. London Main is on 135.375 MHz and covers Amsterdam, Brussels, Dublin, Glasgow, London LGW, London LHR, London STN, Manchester, and Paris CDG. London North is on 126.6 MHz and covers Blackpool, East Midlands, Leeds Bradford, Liverpool, London LGW, Manchester, Newcastle, Isle of Man, and Teeside. London South is on 128.6 MHz and covers Birmingham, Bournemouth, Bristol, Cardiff, Jersey, Luton, Norwich, Southampton, and Southend. Scottish is on 125.725 MHz and covers Aberdeen, Belfast BFS, Edinburgh, Glasgow, Inverness, London LHR, Prestwick, Stornoway, and Sumburgh. Dublin is on 127.0 MHz and covers Dublin, Shannon, Cork, Belfast BFS, Glasgow, Prestwick, Manchester, London LHR, and London LGW. Now HF OFIS. HF OFIS Volmet is broadcast by the Oceanic Control Centres — for example, Shanwick — and it covers the aerodromes used by transiting traffic. So while VHF OFIS serves specific FIRs, HF OFIS serves aircraft crossing the ocean, giving them weather for the airports they’ll use along the way. Now ATIS — Automatic Terminal Information Service. ATIS broadcasts consist of two types: Voice ATIS and Data ATIS. The preparation and dissemination of ATIS is the responsibility of ATS — Air Traffic Services. So ATS is in charge of putting the ATIS together and getting it out. Voice ATIS is provided at aerodromes where there is a requirement to reduce voice channel communications. The idea is to offload routine weather and runway information from the controller’s frequency. ATIS broadcasts comprise one of four configurations: one broadcast serving arriving aircraft; or one broadcast serving departing aircraft; or one broadcast serving both arriving and departing aircraft; or two broadcasts serving arriving or departing aircraft where one broadcast would be exceptionally long. So if the information is too long for a single broadcast, you split it into two — one for arrivals, one for departures. Now the transmission. Voice ATIS is usually transmitted on a discrete VHF frequency, displayed on all aerodrome plates. So you’ll find the ATIS frequency printed on the charts. It may be transmitted on the voice channel of a relevant VOR — for example, departure ATIS on the VOR used as the primary VOR for a SID, or arrival ATIS on the VOR that serves as the IAF for a procedure. So a SID is a Standard Instrument Departure, and the IAF is the Initial Approach Fix. ATIS is never transmitted on the voice channel of ILS — the Instrument Landing System. That’s a hard rule. And Voice ATIS is continuous and repetitive — it repeats the same message over and over so any aircraft can pick it up at any time. So to tie it together: SIGMET and AIRMET are weather warnings; OFIS is the broadcast system that delivers VOLMET — METAR, SIGMET, TAF — on HF or VHF; and ATIS is the automatic terminal information service, either voice or data, prepared by ATS, transmitted on a discrete VHF frequency or a VOR voice channel, never on ILS, and always continuous and repetitive.