FINAL REPORT - Stakeholders - Ofcom

communication services which could, through a transfer of voice to data, alleviate
congestion in the current band.
It is understood that NATS’ intention is to start the process of moving out of VOR
operations as soon as possible. However, NATS has concerns about whether this is
permitted by the terms of its operating licence and whether the need to support general
aviation users would prevent wholescale de-commission of VOR.
One conclusion of the ITU’s World Radiocommunications Conference in 2003 (WRC-
2003) was that consideration for additional radio spectrum allocation for aviation could be
made in the range 108 MHz to 6 GHz including consideration of current satellite
frequency allocations. The ITU would assess new requirements against the overall need
to develop spectrum efficient systems. Consideration of extension of the VHF band could
therefore be made within the terms of this proposed review.
5.6 Possible Improvements to existing technology
5.6.1 VHF voice: 8.33 kHz channelisation
A migration from 25 kHz channels to 8.33 kHz channels has been implemented at high
altitude in Europe, although not extensively yet in the UK. As a result of an equipage
mandate, the air transport fleet is largely equipped with 8.33 kHz capable radios. A more
widespread use of 8.33 kHz is being promoted as a short-term solution to frequency
congestion in the VHF band.
CAA believes that the move to 8.33 kHz would give UK enough spectrum to meet
demand for analogue voice services until 2020 (equivalent figures for Europe as a whole,
tend to quote 2015 as the “saturation point”).
NATS is planning a transition to 8.33 kHz operations although there are a number of
barriers which have acted to slow down implementation:
a) Equipage of general aviation aircraft which acts to limit the potential for
implementation at low altitudes. Note that an effective initial implementation would be
to follow corridors i.e. down to Heathrow since 8.33 kHz is easier to implement at low
level since there is no need for offset carrier systems. However, this would require
widespread equipage in the GA fleet.
b) Difficulties implementing 8.33 kHz over the wide geographic areas serving en-route
sectors. This is because the Climax offset carrier system cannot be used as
effectively with 8.33 kHz since 8.33 kHz cannot contain as many offset carriers as a
25 kHz channel 22 . This limits the potential use of 8.33 kHz to smaller sectors.
c) NATS has identified a number of sectors that could transfer to 8.33 kHz but is
currently unable to implement them because its voice distribution and switching
infrastructure (i.e. the interface between the ground and airborne segments) is not
ready. This restricts the rate of implementation above FL245.
d) Equipage of military aircraft would also need to be addressed prior to
implementation.
22 Note that a recent EUROCONTROL study has highlighted difficulties with current 8.33
kHz radios that may limit even further the opportunity to implement a Climax system.
Clearly more work is required to determine how wide area coverage can be provided in
an 8.33 kHz environment.
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