FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1973
1973 - 2793.PDF
sit FLIGHT International, 15 November (973 "WSSB ••• |f8 Avionics Long-range operational control Icao is reviewing the use by airlines of the HF band for direct communications be tween ground staff and airliners away from base. Such a service for long-range opera tional control is already provided by Inter national Aeradio at London Heathrow using the call sign Speedbird London. Gerald Selves looks at the regulations covering its operation and the advantages of this form of communication. WHILE the VHF band of frequen cies is suitable for short-range communications between ground stations and civil aircraft, for longer ranges it is necessary to use the HF spectrum (3MHz to 30MHz). The use of the HF band is, however, governed by the International Telecommunica tion Union (ITU) regulations and at present it is difficult for Icao member states to authorise the use of these frequencies outside certain geographi cal boundaries. The Air Navigation Commission of Icao is in the process of reviewing the situation and examin ing the implications of the present regulations included in Annex 6 Part I and Annex 10 Part II. Icao plans to meet the demand from airlines for long-range opera tional control activities in two stages. It suggests that immediate demands could be met by accepting the con straints of the present ITU regula tions in which one small family of frequencies is set aside for worldwide use and is exclusive to the aero nautical mobile (ground-to-air) service. In addition to this small family there is a band of frequencies available on a shared basis with the aeronautical fixed (ground-to-ground) service. It is recognised that, while these fre quencies are not sufficient to meet the long-term demands of long-range operational control, they do offer a partial solution if Icao member states are prepared to accept a number of controlling principles. The second step in the Icao plan is designed to provide a longer-term solution. It proposes action through the ITU to revise the allocation of frequencies to make more channels available. To allow Icao to implement the first stage of its plans, members will have to be prepared to accept a number of controls. These are designed to make maximum use of the frequencies now Racal-supplied directional tog periodic antenna At present 12 operators are taking the service using Collins 618Ttransceivers Coubro&Scutton omni - directional -conical antenna Granger Associates directional log periodic antenna Reiceiversite at London Heathrow. SixRacal 1205 receivers Transmitter site at Birdlip, Glos. Dual Marconi H1000 transmitter Operational control room available. First, it is suggested that the total number of ground stations on these worldwide channels should be kept to a minimum. If practical, one station should serve air carrier operating agencies in two or more adjacent Icao states and there should be no more than one station per state. Secondly, the ground station may be operated by the state's post office, air carrier or a communications agency while serving the interests of one or more carriers and operating under a licence issued by the appropriate Icao state. The licence should not allow the transmission of public correspondence or point-to-point traffic. The principles do not appear to be too restrictive, and hopefully suitable amendment to the ITU frequency plan, perhaps by 1976, will make more channels available to relieve the anticipated congestion. Speedbird London Now operating in the United King dom, licensed by the British Civil Aviation Authority, is such a ground station providing aviation interests with facilities for worldwide opera tional control. It transmits within the principles previously mentioned and is licensed to British Airways and operated by International Aeradio. It has the call sign Speedbird London. The station operates on high fre quency single side band—a technique which is gradually replacing the con ventional method of amplitude modu lation. The advantage of SSB is that all the radiated power from the air craft or ground station is concentrated in the band carrying the intelligence, i.e. all the radiated power is in the speech band. The result of trans mitting all the available power in this way is increased radio range, and the coverage with present-day equipment is practically worldwide. The aircraft, of course, needs to be able to transmit and receive SSB and this is now stan dard to new aircraft carrying HF and Telephone circuits Teleprinter circuits Intercommunication circuits The airlines that use Speedbird London include Air Zaire, Aerolineas Argentinas, BEA Airtours, British Airways, British Cale donian, East African Airways, Japan Air Lines, Laker, Nigeria Airways, Pan American, Qantas, Tradewinds and Transmeridian is quite common on most commercial aircraft. The equipment is capable of providing both conventional amplitude modulation and SSB operation and therefore has a dual role for com munications for air traffic control and company operational control. Speedbird London provides opera tional control over most major air routes and some 20 air carriers use the facilities. The station is used for relaying to either aircraft or company office (wherever located) operational data concerning, for example, re routing, engineering snags, passenger information, estimated arrival and departure times and airfield weather forecasts. Messages from aircraft are relayed from the ground station to company offices by telephone or tele printer. The service is open to any aircraft operating agency requiring air-to- ground operational control. The cost is calculated on the basis that the more it is used the cheaper the unit cost becomes. For agencies operating aircraft over 12,0001b, 5,500kg the rates are £42 per month plus £5 for any number of messages per flight sector decreasing to £3 and £1 for more than 300 or 600 messages per year respectively. The first two calls of each month are free and reduced rates are available for agencies opera ting aircraft under 12,0001b, 5,500kg. The SSB radio station at Heathrow provides coverage , of most airline routes, it accepts and relays company communications, is operational 24hr a day, monitors five HF channels simul taneously and is available for selective calling (Selcal) of individual aircraft and for the checking of aircraft radio equipment.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
