Of North Atlantic Radio Communications

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The airspace of the North Atlantic which links Europe and North America is the busiest oceanic airspace in the world. In 2012 approximately 460,000 flights crossed the North Atlantic. For the most part in the North Atlantic, Direct Controller Pilot Communications (DCPC) and ATS Surveillance are unavailable. Aircraft separation assurance and hence safety are nevertheless ensured by demanding the highest standards of horizontal and vertical navigation performance/accuracy and of operating discipline.

The vast majority of North Atlantic flights are performed by commercial jet transport aircraft in the band of altitudes FL290 – FL410. To ensure adequate airspace capacity and provide for safe vertical separations, Reduced Vertical Separation Minima (RVSM) is applied throughout the ICAO NAT Region.

A large portion of the airspace of the North Atlantic Region, through which the majority of these North Atlantic crossings route between FLs 285 and 420 inclusive, is designated as the NAT High Level Airspace (NAT HLA). Within this airspace a formal Approval Process by the State of Registry of the aircraft or the State of the Operator ensures that aircraft meet defined NAT HLA Standards and that appropriate crew procedures and training have been adopted.

The lateral dimensions of the NAT HLA airspace include the following Control Areas (CTAs):
SHANWICK (excluding SOTA & BOTA),
BODO OCEANIC and the portion of
NEW YORK OCEANIC EAST which is north of 27°N.

Pilots MUST NOT fly across the North Atlantic within NAT HLA airspace, nor at flight levels 290 to 410 inclusive anywhere within the NAT Region, unless they are in possession of the appropriate Approval(s) issued by the State of Registry or the State of the Operator. It should be noted that State Approvals for NAT.

Aircraft without NAT HLA MNPS or RVSM Approvals may, of course, also fly across the North Atlantic below FL285, however, weather conditions can be harsh; there are limited VHF radio communications and ground-based navigation aids; and the terrain can be rugged and sparsely populated. International General Aviation (IGA) flights at these lower levels constitute a very small percentage of the overall NAT traffic but they account for the vast majority of Search and Rescue operations.

“For flights over the NAT, ICAO SARPS in Annex 6 (Operation of Aircraft), Part I, Chapter 6 and Part II, Chapter 2.4 requires carriage of Emergency Locator Transmitters (ELTs) by all commercial and IGA aircraft, respectively. It should be further noted that new specifications for these beacons to operate exclusively on frequency 406 MHz (but with a 121.5 MHz search and rescue homing capability) have been in effect since January 2005. New aircraft have been required to be so equipped since 2005.


Exceptions – Special Operations
1.1.7 NAT ATS Providers may approve moving or stationary temporary airspace reservations within NAT HLA Airspace, for the benefit of State or Military Aircraft Operating Agencies to accommodate Military Exercises, Formation Flights, Missile Firing or UAV Activities. Procedures are established in respect of the requests for and management of such reservations. Whenever such reservations might impinge upon other flights in the NAT Region, relevant AIS is published, including, if appropriate, annotations on the NAT Track Message.


1.1.8 Manned Balloon flights can be operated in or through the NAT Region. They are, however, required to avoid NAT HLA airspace and must be meticulously co-ordinated with affected ATS Authorities many months in advance…

..6.1.1…routine airground ATS Voice communications in the NAT Region are conducted via aeradio stations staffed by communicators who have no executive ATC authority. Messages are relayed by the ground station to/from the air traffic controllers in the relevant OAC. This is the case, whether communications are via HF, GP/VHF or SATCOM Voice.

6.1.2 In the North Atlantic Region there are six aeronautical radio stations, one associated with each of the Oceanic Control Areas. They are:

Bodø Radio (Norway, Bodø ACC),
Gander Radio (Canada, Gander OACC),
Iceland Radio (Iceland, Reykjavik ACC),
New York Radio (USA, New York OACC),
Santa Maria Radio (Portugal, Santa Maria OACC) and
Shanwick Radio (Ireland, Shanwick OACC).

However, the aeradio stations and OACs are not necessarily co-located. For example, in the case of Shanwick operations, the OAC is located at Prestwick in Scotland whilst the associated aeradio station is at Ballygirreen in the Republic of Ireland. In addition to those six aeronautical stations, there are two other stations that operate NAT frequencies. They are

Canarias Radio which serves Canarias ACC and
Arctic Radio serving Edmonton, Winnipeg and Montreal ACC’s.

HF Voice Communications

6.1.3 Even with the growing use of datalink communications a significant volume of NAT air/ground communications are conducted using voice on SSB HF frequencies. To support air/ground ATC communications in the North Atlantic Region, twenty-four HF frequencies have been allocated, in bands ranging from 2.8 to 18 MHz.

6.1.4 There are a number of factors which affect the optimum frequency for communications over a specific path. The most significant is the diurnal variation in intensity of the ionisation of the refractive layers of the ionosphere. Hence frequencies from the lower HF bands tend to be used for communications during night-time and those from the higher bands during day-time. Generally in the North Atlantic frequencies of less than 7 MHz are utilised at night and frequencies of greater than 8 MHz during the day.

6.1.5 The 24 NAT frequencies are organized into six groups known as Families. The families are identified as NAT Family A, B, C, D, E and F. Each Family contains a range of frequencies from each of the HF frequency bands. A number of stations share families of frequencies and co-operate as a network to provide the required geographical and time of day coverage.. A full listing of the frequency hours of operation of each NAT aeradio station is contained in the “HF Management Guidance Material for the North Atalntic Region” (NAT Doc 003) (Appendices C- 1 thru 6), available at www.icao.int/EURNAT/, following “EUR & NAT Documents”, then “NAT Documents”, in folder “NAT Doc 003”. Each Family is designated for use by aircraft of specific States of Registry and according to the route to be flown (Is this still true ????). NAT ATS provider State AIPs list the families of frequencies to be used.

6.1.6 Each individual aircraft is normally allocated a primary and a secondary HF frequency, either when it receives its clearance or by domestic controllers shortly before the oceanic boundary.

6.1.7 When initiating contact with an aeradio station the pilot should state the HF frequency in use. HF Radio operators usually maintain a listening watch on more than one single frequency. Identification by the calling pilot of the particular frequency being used is helpful to the radio operator.

6.1.8 When using HF communications and even when using ADS-C and/or CPDLC, pilots should maintain a listening watch on the assigned frequency, unless SELCAL is fitted, in which case they should ensure the following sequence of actions:
a) provide the SELCAL code in the flight plan; (any subsequent change of aircraft for a flight will require passing the new SELCAL information to the OAC);
b) check the operation of the SELCAL equipment, at or prior to entry into Oceanic airspace, with the appropriate aeradio station. (This SELCAL check must be completed prior to commencing SELCAL watch); and
c) maintain thereafter a SELCAL watch.

6.1.9 It is important to note that it is equally essential to comply with the foregoing SELCAL provisions even if SATCOM Voice or ADS/CPDLC are being used for routine air/ground ATS communications. This will ensure that ATC has a timely means of contacting the aircraft.

6.1.10 Flight management staff and crews of aircraft equipped with 12-tone SELCAL equipment should be made aware that SELCAL code assignment is predicated on the usual geographical area of operation of that aircraft. If the aircraft is later flown in geographical areas other than as originally specified by the aircraft operator, the aircraft may encounter a duplicate SELCAL code situation. Whenever an aircraft is to be flown routinely beyond the area of normal operations or is changed to a new geographic operating area, the aircraft operator should contact the SELCAL Registrar and request a SELCAL code appropriate for use in the new area.

6.1.11 When acquiring a previously owned aircraft equipped with SELCAL, many aircraft operators mistakenly assume that the SELCAL code automatically transfers to the purchaser or lessee. This is not true. As soon as practical, it is the responsibility of the purchaser or lessee to obtain a SELCAL code from the Registrar, or, if allocated a block of codes for a fleet of aircraft, to assign a new code from within the block of allocated codes. In the latter instance, if 12-tone equipment is involved, the Registrar should be consulted when there is any question as to the likely geographical area of operation and the possibility of code duplication.

6.1.12 The registrar can be contacted via the AFTN address KDCAXAAG, and by including “ATTN. OPS DEPT. (forward to SELCAL Registrar)” as the first line of message text.


VHF Voice Communications

6.1.13 Aeradio stations are also responsible for the operation of General Purpose VHF (GP/VHF) outlets. North Atlantic flights may use these facilities for all regular and emergency communications with relevant OACs. Such facilities are especially valuable in the vicinity of Iceland, Faroes and Greenland since VHF is not as susceptible to sunspot activity as HF.

Outlets are situated at Prins Christian Sund, which is remotely controlled from Gander Aeradio station, and at Qaqatoqaq, Kulusuk, several locations in Iceland and the Faroes, via Iceland Radio.

When using GP/VHF frequencies in areas of fringe coverage however, care should be taken to maintain a SELCAL watch on HF thus ensuring that if VHF contact is lost the aeradio station is still able to contact the aircraft.

It is important for the pilot to appreciate that when using GP/VHF, as with HF and SATCOM Voice, these communications are with an aeradio station and the pilot is not in direct contact with ATC.

However Direct Controller/Pilot Communications (DCPC) can be arranged, if necessary, via patch-through on some GP/VHF frequencies.

6.1.14 Reykjavik centre operates a number of Direct Controller Pilot Communications (DCPC) VHF stations in Iceland, Faroe Islands and Greenland. At jet flight levels the coverage is approximately 250 NM as indicated in the map below. Those stations are used to provide tactical procedural control and ATS


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