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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).
NORTH ATLANTIC MNPSA OPERATIONS MANUAL CHAPTER 6
NAT MNPS 33 Edition 2005
6.6.7 If not SATCOM equipped try VHF relay via another aircraft (See General Provisions 3. & 4.
above).
Communications Procedures for Use during Poor HF Propagation Conditions
6.6.8 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 occasions, experience resulting HF communications
difficulties.
6.6.9 SATCOM Voice communications are unaffected by most ionospheric disturbances.
Therefore, when so equipped, an aircraft may use SATCOM for ATC communications (See General
Provisions 2 above).
6.6.10 If, however, not SATCOM equipped, in some circumstances it may be feasible to seek the
assistance, via VHF, of a nearby SATCOM equipped aircraft to relay communications with ATC (See
General Provisions 3. & 4. above).
6.6.11 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 contact also broadcast their
position reports.
6.6.12 If for whatever reason SATCOM 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.
6.6.13 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.
6.6.14 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.
6.6.15 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.
NORTH ATLANTIC MNPSA OPERATIONS MANUAL CHAPTER 6
NAT MNPS 34 Edition 2005
Rationale for Lost Communications Operational Procedures
Radar Environment
6.6.16 In an SSR environment ATC has continuous real-time radar 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
　
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