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North Atlantic (NAT)

International Operations Regional

Regional differences from the ICAO standard can be found in ICAO Document 7030 and your Jeppesen Airway Manual. Both of the sources, however, can be out of date. See Regional Introduction for ideas about getting up-to-date information.


There are a lot of communications procedures that we assume are required worldwide. In truth, about the only place you will find these specified are in NAT Doc 007. So they best practices just about everywhere in the world and they are mandatory in the North Atlantic.

ATS Communications

[NAT Doc 007, ¶6.1]

  • It is important that pilots appreciate that routine air/ground 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.
  • 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

  • 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.
  • 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.
  • 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 frequencies operated by each NAT aeradio station is contained in the “HF Management Guidance Material for the North Atlantic Region” (NAT Doc 003) (Appendices B- 1 thru 6), available at, following “EUR & NAT Documents”, then “NAT Documents”, in folder “NAT Doc 003”.
  • 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.
  • 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.


  • 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:
    • 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);
    • 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
    • maintain thereafter a SELCAL watch.
  • 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.
  • 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.

  • SATCOM Voice Communication

  • In 2011 following successful trials, it was agreed that Aeronautical Mobile Satellite (Route) Service (AMS(R)S), more commonly referred to as SATCOM Voice, can be used as a supplement to HF communications throughout the NAT Region for any routine, non-routine or emergency ATS air/ground communications. NAT ATS Provider State AIPs contain the necessary telephone numbers and/or short-codes for air-initiated call access to aeradio stations and/or direct to OACs. Since oceanic traffic typically communicate with ATC through aeradio facilities, routine SATCOM Voice calls should be made to such a facility rather than the ATC Centre. Only when the urgency of the communication dictates otherwise should SATCOM Voice calls be made to the ATC Centre. SATCOM voice communication initiated due to HF propagation difficulties does not constitute urgency and should be addressed to the air-ground radio facility.
  • The provisions governing the use of SATCOM Voice for ATS communications in the NAT Region are contained in ICAO NAT SUPPS (Doc.7030/5) Section 3.4. These provisions include that even assigned HF frequency.
  • Operators must also recognise that they are bound by their own State of Registry’s regulations regarding carriage and use of any and all long-range ATS communications equipment. Some States do not authorise the carriage of SATCOM as redundancy for HF equipage. However, in other instances MMEL remarks for HF systems do provide relief for SATCOM Voice equipped aircraft, thereby making the requirement for the carriage of fully serviceable/redundant HF communications equipment less of an issue (See also Section 6.6 below regarding the use of SATCOM in the event of “HF Communications Failure”).

  • Data Link Communications

  • Data link communications are gradually being introduced into the NAT environment for position reporting (via FANS 1/A ADS-C & CPDLC) and for other air/ground ATS exchanges (using FANS 1/A CPDLC). NAT Region specific guidance may be published in NAT OPS Bulletins when deemed necessary by the NAT SPG and the operational procedures to be used are specified in the “Global Operational Data Link Document (GOLD)”, both of which can be downloaded from, following “EUR & NAT Documents”, then “NAT Documents”. AIS publications of the NAT ATS Provider States should be consulted to determine the extent of current implementation in each of the North Atlantic OCAs.
  • The ICAO GOLD, now known as ICAO Doc 10037, is no longer available there. In fact, you will be hard pressed to find a free copy anywhere. You can find a copy for $242, here:, and once you've downloaded that, you will have a copy protected file that cannot be transfered to an iPad or shared amongst members of your flight department. Of course this is a problem because most data link authorizations require that you have a copy on the flight deck. An anonymous reader sent in this copy: ICAO Doc 10037, which is not as readable and can't be searched for text, but it does satisfy the requirement to have a copy.

  • On first contact with the initial aeradio stations crews of participating aircraft should expect to receive the instruction “VOICE POSITION REPORTS NOT REQUIRED”.
  • We haven't been hearing this in a while so I asked on frequency. The radio operator told me they stopped saying "Voice Position Reports not Required" because "everyone knows that."

  • Similar to SATCOM Voice usage, Pilots electing to use Data link communications for regular ATS communications in the ICAO NAT Region remain responsible for operating SELCAL (including completion of a SELCAL Check), or maintaining a listening watch on the assigned HF frequency.
  • Flights equipped with FANS CPDLC and /or ADS-C should ensure that the data link system is logged on to the appropriate control area when operating within the NAT south of 80 North. This applies even when the aircraft is provided with ATS surveillance services. CPDLC provides communication redundancy and controllers will in many cases use CPDLC for communication even though the pilot is maintaining a listening watch on the assigned DCPC VHF frequency. ADS-C furthermore enables ATC to perform route conformance monitoring for downstream waypoints.
  • Phase 2A of the NAT Data Link Mandate was implemented 05 February 2015. In this phase the NAT DLM airspace was expanded to include all OTS tracks at FLs 350 to 390, inclusive. Only aircraft with functioning CPDLC and ADS-C may plan and/or fly in the height band FL350-390 inclusive on any OTS Track.
  • If a flight experiences an equipment failure AFTER departure which renders the aircraft non-DLM compliant, requests to operate in the NAT Region Data Link Airspace will be considered on a tactical basis. Such flights must indicate their non-DLM status prior to entering the airspace. If the failure occurs while the flight is in NAT Region Data Link Mandate Airspace, ATC must be immediately advised. Such flights may be re-cleared so as to avoid the airspace, but consideration will be given to allowing the flight to remain in the airspace, based on tactical considerations.
  • If a flight experiences an equipment failure PRIOR to departure which renders the aircraft non-DLM compliant, the flight should not flight plan to enter the NAT Regional DLM Airspace.


  • The frequency 121.5 MHz should be continuously monitored by all aircraft operating in the NAT Region so as to be prepared to offer assistance to any other aircraft advising an emergency situation.
  • An air-to-air VHF frequency has been established for world-wide use when aircraft are out of range of VHF ground stations which utilise the same or adjacent frequencies. This frequency, 123.45 MHz, is intended for pilot-to-pilot exchanges of operationally significant information (N.B. It is not to be used as a “chat” frequency).
  • 123.45 MHz may be used to relay position reports via another aircraft in the event of an airground communications failure.
  • This frequency (123.45 MHz) may also be used by pilots to contact other aircraft when needing to coordinate offsets required in the application of the Strategic Lateral Offset Procedures (SLOP).
  • If necessary initial contact for relays or offset coordination can be established on 121.5 MHz, although great care must be exercised should this be necessary, in case this frequency is being used by aircraft experiencing or assisting with an ongoing emergency.
  • Therefore in order to minimise unnecessary use of 121.5 MHz, it is recommended that when possible aircraft additionally monitor 123.45 MHz when flying through NAT airspace.

[NAT Doc 007, ¶6.3] 6.3 POSITION REPORTING

Time and Place of Position Reports

  • Unless otherwise requested by Air Traffic Control, position reports from flights on routes which are not defined by designated reporting points should be made at the significant points listed in the flight plan.
  • Air Traffic Control may require any flight operating in a North/South direction to report its position at any intermediate parallel of latitude when deemed necessary.
  • In requiring aircraft to report their position at intermediate points, ATC is guided by the requirement to have positional information at approximately hourly intervals and also by the need to accommodate varying types of aircraft and varying traffic and MET conditions.
  • Unless providing position reports via ADS-C, if the estimated time for the ‘next position’, as last reported to ATC, has changed by three minutes or more, a revised estimate must be transmitted to the ATS unit concerned as soon as possible.
  • This is one of the few regions in the world that makes this provision in writing, but it is "understood" to be true elsewhere.

  • Pilots must always report to ATC as soon as possible on reaching any new cruising level.

  • Contents of Position Reports

  • For flights outside domestic ATS route networks, position should be expressed in terms of latitude and longitude except when flying over named reporting points. For flights whose tracks are predominantly east or west, latitude should be expressed in degrees and minutes, longitude in degrees only. For flights whose tracks are predominantly north or south, latitude should be expressed in degrees only, longitude in degrees and minutes. However, it should be noted that when such minutes are zero then the position report may refer solely to degrees (as per examples below).
  • All times should be expressed in four digits giving both the hour and the minutes UTC.
  • Radio operators may simultaneously monitor and operate more than one frequency. Therefore, when initiating an HF voice contact it is helpful if the pilot include advice on the frequency being used (see examples below).

  • Standard Message Types

  • Standard air/ground message types and formats are used within the NAT Region and are published in State AIPs and Atlantic Orientation charts. To enable ground stations to process messages in the shortest possible time, pilots should observe the following rules:
    1. use the correct type of message applicable to the data transmitted;
    2. state the message type in the contact call to the ground station or at the start of the message;
    3. adhere strictly to the sequence of information for the type of message;
    4. all times in any of the messages should be expressed in hours and minutes UTC.

    Addressing of Position Reports

  • Position reports for aircraft operating on tracks through successive points on the mutual boundary of two OCAs (e.g. when routing along the 45ºN parallel), should be made to both relevant OACs. (In practice this only requires an addition to the address. (e.g. “Shanwick copy Santa Maria”.)
  • The MNPS has been replaced by the North Atlantic High Level Airspace (NAT HLA) but ICAO Doc 7030 hasn't caught up yet. For now, you can just associate NAT HLA with MNPS.

    More about this: North Atlantic Airspace (NAT HLA).

    This region is moving from a mix of navigation requirements to the system of Performance Based Navigation outlined in ICAO Document 9613. Current navigation requirements are available on Jeppesen Airway Manual Air Traffic Control pages and Chapter 4 of each region covered by ICAO Document 7030.

    RNAV 10 (RNP 10)

    [ICAO Doc 7030 Amendment 1, §NAT, ¶]

    • A lateral separation minimum of 93 km (50 NM) may be applied between flights operating within the control area of the New York Oceanic FIR.
    • The aircraft and operator must be approved RNP 10 or RNP 4 by the State of the Operator or the State of Registry, as appropriate. RNP 10 is the minimum navigation specification for the application of 93 km (50 NM) lateral separation.

    More about this:Required Navigation Performance-10 (RNP-10).

    Keep in mind RNP 10 is an exception to the rule of Required Navigation Performance standards, "RNAV 10" retains the "RNP 10" designation for matters of convenience.

    Minimum Navigation Performance Specifications (MNPS)

    [ICAO Doc 7030 Amendment 1, §NAT, ¶]

    • The MNPS shall be applicable in that volume of airspace between FL 285 and FL 420 within the Oceanic Control Areas of Santa Maria, Shanwick, Reykjavik, Gander Oceanic and New York Oceanic, excluding the area west of 60°W and south of 38°30′N.
    • For flights within the volume of airspace specified in aircraft shall have lateral navigation performance capability such that:
      1. the standard deviation of lateral track errors shall be less than 11.7 km (6.3 NM);
      2. the proportion of the total flight time spent by aircraft 56 km (30 NM) or more off the cleared track shall be less than 5.3 × 10-4; and
      3. the proportion of the total flight time spent by aircraft between 93 and 130 km (50 and 70 NM) off the cleared track shall be less than 1.3 × 10-5.

    WGS-84 Compliance

    All three countries listed in the NAT region, the Azores, Greenland, and Iceland are listed as WGS-84 in the Jeppesen WGS-84 website, but Greenland is listed only as partially compliant in their Jeppesen Airway Manual ATC page, dated 16 Aug 2013.

    More about this: World Geodetic System 84 (WGS-84).


    Operation of your transponder is standard with the exception of the need to wait 30 minutes before switching to Code 2000.


  • All aircraft operating as IFR flights in the NAT Region shall be equipped with a pressure altitude reporting SSR transponder. Unless otherwise directed by ATC, pilots flying in the NAT FIRs will operate transponders continuously in Mode A/C Code 2000, except that the last assigned code will be retained for a period of 30 minutes after entry into NAT airspace or after leaving a radar service area. Pilots should note that it is important to change from the last assigned domestic code to the Mode A/C Code 2000 since the original domestic code may not be recognised by the subsequent Domestic Radar Service on exit from the oceanic airspace. One exception to this requirement should be noted. Because of the limited time spent in the NAT HLA, when flying on Route Tango 9, the change from the last assigned domestic code to Code 2000 should be made Northbound 10 minutes after passing BEGAS and Southbound 10 minutes after passing LASNO.
  • It should be noted that this procedure does not affect the use of the special purpose codes (7500, 7600 and 7700) in cases of unlawful interference, radio failure or emergency. However, given the current heightened security environment crews must exercise CAUTION when selecting Codes not to inadvertently cycle through any of these special purpose codes and thereby possibly initiate the launching of an interception.
  • Reykjavik ACC provides a radar control service in the south-eastern part of its area and consequently transponder codes issued by Reykjavik ACC must be retained throughout the Reykjavik OCA until advised by ATC.
  • RVSM

    [ICAO Doc 7030 Amendment 1, §NAT, ¶4.2.1.] RVSM shall be applicable in that volume of airspace between FL 290 and FL 410 inclusive in all FIRs of the NAT Region.

    Altimeter Procedures

    Transition altitude and level procedures vary by country.

    Special Routings

    The Organized Track System (OTS) carries with it all the restrictions of flying in the NAT HLA plus a few more. You must also be careful in that there are several layers of authorizations involved. You could be permitted the lower altitudes and standard spacing, all altitudes with the chance of decreased longitudinal spacing, and all altitudes with the chance of decreased longitudinal and lateral spacing.


    Photo: Example of Daytime Westbound NAT Organized Track System, NAT Doc 007, Figure 2.

    Click photo for a larger image

    [NAT Doc 007, ¶2.1]

    • As a result of passenger demand, time zone differences and airport noise restrictions, much of the North Atlantic (NAT) air traffic contributes to two major alternating flows: a westbound flow departing Europe in the morning, and an eastbound flow departing North America in the evening. The effect of these flows is to concentrate most of the traffic uni-directionally, with peak westbound traffic crossing the 30W longitude between 1130 UTC and 1900 UTC and peak eastbound traffic crossing the 30W longitude between 0100 UTC and 0800 UTC.
    • Due to the constraints of large horizontal separation criteria and a limited economical height band (FL310–400) the airspace is congested at peak hours. In order to provide the best service to the bulk of the traffic, a system of organised tracks is constructed to accommodate as many flights as possible within the major flows on or close to their minimum time tracks and altitude profiles. Due to the energetic nature of the NAT weather patterns, including the presence of jet streams, consecutive eastbound and westbound minimum time tracks are seldom identical. The creation of a different organised track system is therefore necessary for each of the major flows. Separate organised track structures are published each day for eastbound and westbound flows. These track structures are referred to as the Organised Track System or OTS.
    • It should be appreciated, however, that use of OTS tracks is not mandatory. Currently about half of NAT flights utilise the OTS. Aircraft may fly on random routes which remain clear of the OTS or may fly on any route that joins or leaves an outer track of the OTS. There is also nothing to prevent an operator from planning a route which crosses the OTS. However, in this case, operators must be aware that whilst ATC will make every effort to clear random traffic across the OTS at published levels, re-routes or significant changes in flight level from those planned are very likely to be necessary during most of the OTS traffic periods.
    • Over the high seas, the NAT Region is primarily Class A airspace (at and above FL60) (See ICAO Doc. 7030 - NAT Regional Supplementary Procedures), in which Instrument Flight Rules (IFR) apply at all times. Throughout the NAT Region, below FL410, 1000 feet vertical separation is applied. However, airspace utilisation is under continual review, and within the HLA portion of NAT airspace, in addition to the strategic and tactical use of ‘opposite direction’ flight levels during peak flow periods the Mach Number Technique is applied.

    [NAT Doc 007, ¶2.2 - 2.4]

    • The night-time OTS is produced by Gander OAC and the day-time OTS by Shanwick OAC (Prestwick), each incorporating any requirement for tracks within the New York, Reykjavik, Bodø and Santa Maria Oceanic Control Areas (OCAs).
    • Subsequently, following the initial construction of the NAT tracks by the publishing agencies (Gander OAC for Eastbound tracks and Shanwick OAC for Westbound tracks), the proposed tracks are published on an internet site for interested parties to view and discuss. One hour is allocated for each of the proposals during which any comments will be considered by the publishing agency and any changes which are agreed are then incorporated into the final track design. This internet site is currently operated by NAV CANADA. Access to this site is by password which any bona fide NAT operator may obtain on application to NAV CANADA - see Canada AIP for details.
    • The agreed OTS is promulgated by means of the NAT Track Message via the AFTN to all interested addressees. A typical time of publication of the day-time OTS is 2200 UTC and of the night-time OTS is 1400 UTC.
    • The hours of validity of the two Organised Track Systems (OTS) are normally as follows:
      • Day-time OTS 1130 UTC to 1900 UTC at 30°W
      • Night-time OTS 0100 UTC to 0800 UTC at 30°W
    • To ensure a smooth transition from night-time to day-time OTSs and vice-versa, a period of several hours is interposed between the termination of one system and the commencement of the next. These periods are from 0801 UTC to 1129 UTC: and from 1901 UTC to 0059 UTC.
    • During the changeover periods some restrictions to flight planned routes and levels are imposed. Eastbound and westbound aircraft operating during these periods should file flight level requests in accordance with the Flight Level Allocation Scheme (FLAS) as published in the UK and Canada AIPs.

    ICAO Differences

    Each country departs in some ways with the ICAO standard and common US practices. Pilots should always refer to the Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures pages for each country on their itineraries for differences with ICAO Standards, Recommended Practices and Procedures. More about this: US versus ICAO.

    The following are a sampling of some of the differences, there are many more. You should check the Jeppesen Airway Manual State pages for every country you takeoff, overfly, or land.

    Lost Communications

    [NAT Doc 007, ¶6.6]

    • Rules and procedures for the operation of an aircraft following a radio communications failure (RCF) are established to allow ATC to anticipate that aircraft’s subsequent actions and thus for ATC to be able to provide a service to all other flights within the same vicinity, so as to ensure the continued safe separation of all traffic. The general principles of such rules and procedures are set out in Annexes 2 and 10 to the ICAO Convention. States publish in their AIPs specific RCF rules and regulations to be followed within their particular sovereign airspace.
    • It must be recognised that there is in general an underlying premise in “normal” radio communications failure procedures that they are for use when a single aircraft suffers an on-board communications equipment failure. Within the NAT Region and some adjacent domestic airspace (e.g. Northern Canada), where HF Voice is used for air-ground ATC communications, ionospheric disturbances resulting in poor radio propagation conditions can also interrupt these communications. While it is impossible to provide guidance for all situations associated with an HF communications failure, it is, however, extremely important to differentiate between two distinct circumstances: - firstly, an on-board communications equipment failure, resulting in an individual aircraft losing HF communications with ATC and; secondly, the occurrence of poor HF propagation conditions (commonly referred to as “HF Blackouts”), which can simultaneously interrupt HF air-ground communications for many aircraft over a wide area.
    • In the case of an on-board communications equipment failure, even though ATC loses contact with that aircraft, it can anticipate that aircraft’s actions and, if necessary, modify the profiles of other aircraft in the same vicinity in order to maintain safe separations.
    • However, the occurrence of poor HF propagation conditions can simultaneously interrupt HF air-ground communications for many aircraft over a wide area and ATC may then be unable to make any interventions to assure safe traffic separations using HF. Notwithstanding the growing use of Data link and SATCOM Voice for regular air-ground ATS communications in the NAT Region, all pilots must recognise that, pending the mandatory carriage and use of such means, an HF blackout will impact the ability of ATC to ensure the safe separation of all traffic. Hence, even if using other than HF for regular communications with ATC, pilots should still exercise appropriate caution when HF blackout conditions are encountered.
    • The following procedures are intended to provide general guidance for aircraft which experience a communications failure while operating in, or proposing to operate in, the NAT Region,. These procedures are intended to complement and not supersede State procedures/regulations.

    • General Provisions

      1. The pilot of an aircraft experiencing a two-way ATS communications failure should operate the SSR Transponder on identity Mode A Code 7600 and Mode C.
      2. When so equipped, an aircraft should use Satellite Voice Communications to contact the responsible aeradio station via special telephone numbers/short codes published in State AIPs (see also “HF Management Guidance Material for the NAT Region”). However, it must be appreciated that pending further system developments and facility implementations the capability for Ground(ATC)-initiated calls varies between different NAT OACs.
      3. If the aircraft is not equipped with SATCOM Voice then the pilot should attempt to use VHF to contact any (other) ATC facility or another aircraft, inform them of the difficulty, and request that they relay information to the ATC facility with which communications are intended.
      4. The inter-pilot air-to-air VHF frequency, 123.45 MHz, may be used to relay position reports via another aircraft. (N.B. The emergency frequency 121.5 MHz should not be used to relay regular communications, but since all NAT traffic is required to monitor the emergency frequency, it may be used, in these circumstances, to establish initial contact with another aircraft and then request transfer to the inter-pilot frequency for further contacts).
      5. In view of the traffic density in the NAT Region, pilots of aircraft experiencing a two-way ATS communications failure should broadcast regular position reports on the inter-pilot frequency (123.45 MHz) until such time as communications are re-established.

      Communications Procedures for Use in the Event of an On-board HF Equipment Failure

    • Use SATCOM Voice communications, if so equipped. (See General Provisions 2. above).
    • If not SATCOM Voice equipped try VHF relay via another aircraft (See General Provisions 3. & 4 above).

    • Communications Procedures for Use during Poor HF Propagation Conditions

    • Poor HF propagation conditions are the result of ionospheric disturbances. These are usually caused by sun-spot or solar flare activity creating bursts of charged particles in the solar wind which can spiral down around the Earth’s magnetic lines of force and distort or disturb the ionised layers in the stratosphere which are utilised to refract HF radio waves. As with the Aurora Borealis, which is of similar origin, these ionospheric disturbances most commonly occur in regions adjacent to the Magnetic Poles. Since the Earth’s North Magnetic Pole is currently located at approximately 87N 150W, flights through the North Atlantic and Northern Canada regions can, on occasion, experience resulting HF communications difficulties.
    • SATCOM Voice communications are unaffected by most ionospheric disturbances. Therefore, when so equipped, an aircraft may use SATCOM Voice for ATC communications (See General Provisions 2 above).
    • If not SATCOM Voice equipped, in some circumstances it may be feasible to seek the assistance, via VHF, of a nearby SATCOM Voice equipped aircraft to relay communications with ATC (See General Provisions 3. & 4. above).
    • Whenever aircraft encounter poor HF propagation conditions that would appear to adversely affect air-ground communications generally, it is recommended that all pilots then broadcast their position reports on the air-to-air VHF frequency 123.45 MHz. Given the density of traffic in the NAT Region and the fact that in such poor propagation conditions ATC will be unable to maintain contact with all aircraft, it is important that even those aircraft that have been able to establish SATCOM Voice contact also broadcast their position reports.
    • If for whatever reason SATCOM Voice communications (direct or relayed) are not possible, then the following procedures may help to re-establish HF communications. Sometimes these ionospheric disturbances are very wide-spread and HF air-ground communications at all frequencies can be severely disrupted throughout very large areas (e.g. simultaneously affecting the whole of the NAT Region and the Arctic.). However, at other times the disturbances may be more localised and/or may only affect a specific range of frequencies.
    • In this latter circumstance, HF air-ground communications with the intended aeradio station may sometimes continue to be possible but on a frequency other than either the primary or secondary frequencies previously allocated to an aircraft. Hence, in the event of encountering poor HF propagation conditions pilots should first try using alternative HF frequencies to contact the intended aeradio station.
    • However, while the ionospheric disturbances may be severe, they may nevertheless only be localized between the aircraft’s position and the intended aeradio station, thus rendering communications with that station impossible on any HF frequency. But the aeradio stations providing air-ground services in the NAT Region do co-operate as a network and it may, even then, still be possible to communicate with another aeradio station in the NAT network on HF and request that they relay communications. Efforts should therefore be made to contact other NAT aeradio stations via appropriate HF frequencies.
    • Nevertheless, as previously indicated, there are occasions when the ionospheric disturbance is so severe and so widespread that HF air-ground communications with any aeradio station within the NAT Region network are rendered impossible.

    • Rationale for Lost Communications Operational Procedures

    • Because of the density of oceanic traffic in the NAT Region, unique operational procedures have been established here to be followed by pilots whenever communications are lost with ATC. These procedures and the rationale for their development follow.

    • Tactical ATC Environment

    • In a tactical ATC environment,, such as one in which ATS Surveillance and VHF voice communications are used, ATC has continuous real-time data on the position/progress of all relevant traffic and the intentions of any individual aircraft with which ATC may have lost communications can be inferred from that aircraft’s filed flight plan. Hence, in such an environment, when voice communications with a single aircraft fail, the relevant published “lost comms procedures” normally require that aircraft to “land at a suitable aerodrome or continue the flight and adjust level and speed in accordance with the filed flight plan”. Communications blackouts affecting multiple aircraft, are not a feature of this type of VHF environment and hence in these circumstances, if required, ATC will be able to re-clear other traffic to ensure safe separations are maintained.

    • Procedural ATC Environment

    • However, in a (largely) non-ATS surveillance environment such as the North Atlantic, ATC must rely significantly upon the HF Voice Position Reports communicated by each aircraft for position, progress and intent data. Communications equipment failures and/or poor propagation conditions can interrupt the provision of this information. Therefore, to mitigate against such occurrences in the busy NAT HLA, outside of VHF coverage, ATC often employs strategic traffic planning and issues Oceanic Clearances which have been pre-co-ordinated with downstream OACs. Flights that continue to follow such a pre-coordinated strategic oceanic clearance are thereby guaranteed conflict-free progress to oceanic exit, even if no ATS communications are subsequently possible with any one, or even with all, of those strategically planned aircraft.
    • Every effort is made by the initial NAT OAC to clear aircraft as per their filed flight plans. However, this is not always possible, particularly during peak traffic flow periods. Aircraft may receive clearances at flight levels or speeds other than those flight planned or, less frequently, may be cleared on oceanic tracks via entry or exit points other than those contained in the filed flight plan. Also it must be recognized that while a filed NAT flight plan may contain one or more step climbs for execution within the NAT Region, the initially issued oceanic clearance, or even any subsequently updated clearance (i.e. reclearance), has only been co-ordinated for a single ( i.e. initial or current) flight level. It must therefore be appreciated that it is only the flight routing and profile contained in the last received clearance that ATC has probed for conflicts. Unless this clearance is precisely the same as the filed flight plan, in any lost communications situation in the NAT Region, if a pilot in receipt of a clearance unilaterally reverts to his/her filed flight plan (even by simply executing a later step climb), then no guarantee of conflict-free progress exists. Consequently, if a NAT aircraft loses the possibility of communications with the relevant OAC at any time after receiving and acknowledging a clearance, and the pilot elects to continue the flight, then the aircraft must adhere strictly to the routing and profile of the last received clearance until exiting the NAT Region. Pilots must not unilaterally revert to their filed flight plan.

    These are exceptions to ICAO Lost Comm procedures.

    More about this: Lost Communications.

    Strategic Lateral Offset Procedure (SLOP)

    [NAT Doc 007, ¶8.5.3] Distributing aircraft laterally and equally across the three available positions adds an additional safety margin and reduces collision risk. SLOP is now a standard operating procedure for the entire NAT Region and pilots are required to adopt this procedure as is appropriate. In this connection, it should be noted that:

    1. Aircraft without automatic offset programming capability must fly the centreline.
    2. If you have automatic offset programming capability, you MUST SLOP in the North Atlantic. If you do not have automatic offset programming capability, you MAY NOT SLOP.

    3. To achieve an equal distribution of flying the centreline or 1 NM (one nautical mile) right or 2 NM (two nautical miles) right of centerline, it is recommended that pilots of aircraft capable of programming automatic offsets should randomly select flying centreline or an offset. (See Note in 8.5.2 a) above) In order to obtain lateral spacing from nearby aircraft (i.e. those immediately above and/or below), pilots should use whatever means are available (e.g. ACAS/TCAS, communications, visual acquisition, GPWS) to determine the best flight path to fly.
    4. An aircraft overtaking another aircraft should offset within the confines of this procedure, if capable, so as to create the least amount of wake turbulence for the aircraft being overtaken.
    5. For wake turbulence purposes, pilots should fly one of the three positions shown above. Pilots should not offset to the left of centreline nor offset more than 2 NM right of centreline. Pilots may contact other aircraft on the air-to-air channel, 123.45 MHz, as necessary; to coordinate the best wake turbulence mutual offset option. (Note. It is recognized that the pilot will use his/her judgement to determine the action most appropriate to any given situation and that the pilot has the final authority and responsibility for the safe operations of the aeroplane. See also Chapter 13, paragraph 13.5.) As indicated below, contact with ATC is not required.
    6. Pilots may apply an offset outbound at the oceanic entry point and must return to centreline prior to the oceanic exit point unless otherwise authorized by the appropriate ATS authority or directed by the appropriate ATC unit.
    7. Aircraft transiting ATS Surveillance-controlled airspace mid-ocean should remain on their already established offset positions.
    8. There is no ATC clearance required for this procedure and it is not necessary that ATC be advised.
    9. Voice Position reports should be based on the waypoints of the current ATC clearance and not the offset positions.

    If you have automatic offset capability, SLOP is mandatory for you in the North Atlantic.

    More about this: Strategic Lateral Offset Procedure (SLOP).

    See Also

    Airspace: North Atlantic High Level Airspace (NAT HLA)

    Oceanic Clearance

    Book Notes

    Portions of this page can be found in the book International Operations Flight Manual, Part III, Chapter 7.


    ICAO Doc 7030 - Regional Supplementary Procedures, International Civil Aviation Organization, 2008

    ICAO Doc 7030, Amendment 1, International Civil Aviation Organization, 8 January 2009

    ICAO Doc 7030, Amendment 9, International Civil Aviation Organization, 2 October 2017

    Jeppesen Airway Manual

    ICAO NAT Doc 007, North Atlantic Operations and Airspace Manual, v 2018-1

    Revision: 20180210