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Guidance concerning Air Navigation in and above the NAT MNPSA


(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

      • 6.6.6

        Use SATCOM Voice communications, if so equipped. (See General Provisions 2. above).

      • 6.6.7

        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 80N 110W, flights through the North Atlantic and Northern Canada regions can, on occasion, experience resulting HF communications



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

NAT Doc 007


Edition 2010

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