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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
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 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 35 Edition 2009
Rationale for Lost Communications Operational Procedures
Tactical ATC Environment
6.6.16 In a tactical ATC environment,, such as one in which Secondary Surveillance Radar 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
6.6.17 However, in a (largely) non-radar 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 MNPS
airspace, outside of VHF coverage ATC often employs strategic traffic planning and issues Oceanic
Clearances which have been pre-co-ordinated with downstream OACs. Thereby ensuring that flights
　
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