World Air Ops | NAT | Doc 007 MNPS Guidance

Guidance concerning Air Navigation in and above the NAT MNPSA CHAPTER 6disturbances are very wide-spread and HF air-ground communications at all frequencies can be severelydisrupted throughout very large areas (e.g. simultaneously affecting the whole of the NAT Region and theArctic.). However, at other times the disturbances may be more localised and/or may only affect a specificrange of frequencies.6.6.13 In this latter circumstance, HF air-ground communications with the intended aeradio stationmay sometimes continue to be possible but on a frequency other than either the primary or secondaryfrequencies previously allocated to an aircraft. Hence, in the event of encountering poor HF propagationconditions 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 belocalized between the aircraft’s position and the intended aeradio station, thus rendering communicationswith that station impossible on any HF frequency. But the aeradio stations providing air-ground services inthe NAT Region do co-operate as a network and it may, even then, still be possible to communicate withanother aeradio station in the NAT network on HF and request that they relay communications. Effortsshould 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 disturbanceis so severe and so widespread that HF air-ground communications with any aeradio station within the NATRegion network are rendered impossible.Rationale for Lost Communications Operational Procedures6.6.16 Because of the density of oceanic traffic in the NAT Region, unique operational procedureshave been established here to be followed by pilots whenever communications are lost with ATC. Theseprocedures and the rationale for their development follow.Tactical ATC Environment6.6.17 In a tactical ATC environment,, such as one in which Secondary Surveillance Radar andVHF voice communications are used, ATC has continuous real-time data on the position/progress of allrelevant traffic and the intentions of any individual aircraft with which ATC may have lost communicationscan be inferred from that aircraft’s filed flight plan. Hence, in such an environment, when voicecommunications with a single aircraft fail, the relevant published “lost comms procedures” normally requirethat aircraft to “land at a suitable aerodrome or continue the flight and adjust level and speed in accordancewith the filed flight plan”. Communications blackouts affecting multiple aircraft, are not a feature of thistype of VHF environment and hence in these circumstances, if required, ATC will be able to re-clear othertraffic to ensure safe separations are maintained.Procedural ATC Environment6.6.18 However, in a (largely) non-radar environment such as the North Atlantic, ATC must relysignificantly upon the HF Voice Position Reports communicated by each aircraft for position, progress andintent data. Communications equipment failures and/or poor propagation conditions can interrupt theprovision of this information. Therefore, to mitigate against such occurrences in the busy NAT MNPSairspace, outside of VHF coverage, ATC often employs strategic traffic planning and issues OceanicClearances which have been pre-co-ordinated with downstream OACs. Flights that continue to follow sucha 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 thosestrategically planned aircraft.6.6.19 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 receiveNAT Doc 007 38 Edition 2010