Guidance concerning Air Navigation in and above the NAT MNPSA
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 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 communications
from with a
single aircraft fail, the relevant published “lost
such an environment, when voice comms procedures” normally require
that aircraft to “land at a suitable aerodrome or continue the flight and adjust level with the filed flight plan”. Communications blackouts affecting multiple aircraft, type of VHF environment and hence in these circumstances, if required, ATC will
and speed in accordance are not a feature of this be able to re-clear other
traffic to ensure safe separations are maintained.
Procedural ATC Environment
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 propagation conditions can interrupt the
provision of this airspace, outside Clearances which a pre-coordinated even if no ATS
information. Therefore, to mitigate against such occurrences in the busy NAT MNPS of VHF coverage, ATC often employs strategic traffic planning and issues Oceanic have been pre-co-ordinated with downstream OACs. Flights that continue to follow such strategic oceanic clearance are thereby guaranteed conflict-free progress to oceanic exit, 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
NAT Doc 007