FINAL REPORT - Stakeholders - Ofcom

• migration to 8.33 kHz spacing for voice services increasing spectrum efficiency
by a factor of between 2 and 3.
• migration of a VDL Mode 2 network to a more efficient solution within the VHF
band increasing the efficiency for transmission of AOC data by a factor of
between 2 and 3 on top of the improvement by a factor 10 achieved in the
migration ACARS to VDL Mode 2.
• migration of voice services to data within or outside the VHF band with an
accompanying reduction of voice services.
5.11.3 Short term measures
Recommendation 5.1: An urgent first measure is to promote the migration to 8.33 kHz
spacing in the VHF band. This measure will alleviate the immediate shortage of VHF
spectrum and facilitate the establishment of digital services.
Implementation for high level sectors is limited by ground infrastructure limitations which
NATS is addressing although no solution is currently apparent for air traffic sectors which
cover a wide geographic area. For low level implementation, the barrier is GA equipage
and an investigation of possible means to stimulate GA equipage should be carried out.
Ofcom should work with the CAA to encourage the implementation of 8.33 kHz spacing
including accelerating the necessary changes to the NATS infrastructure and considering
the issue of, and a possible means of stimulating, GA equipage.
Socio-economic factors
Firstly consider the value of VHF spectrum to NATS operations. For illustration purposes,
it is assumed that NATS annual turnover from airline fees is of the order of £500M per
annum with typically 8% profit before tax 24 . All spectrum allocated to the communication,
navigation and surveillance infrastructure is required to support this level of turnover.
Taking the case of VHF voice communications, it will be assumed there are
approximately 500 25 kHz channels dedicated to air traffic control. Each channel is
therefore supporting revenue of £1M per year and profit before tax of about £80k per
year.
Since each 25 kHz voice channel could be divided into three, NATS has the potential to
generate an additional £160k per year from a 25 kHz channel by moving to 8.33 kHz
channelisation. It is unlikely that an increase of efficiency by a factor 3 could be achieved
because of re-use distance considerations. Assuming more conservatively that the
increase in efficiency is a factor of 2, the additional profit is £80k per year.
Hence there is a clear motivation for NATS to secure sufficient spectrum allocation to
support the growth of air traffic.
As indicated earlier in this section, there are a number of barriers to converting to 8.33
kHz:
• NATS must update its infrastructure
• the GA fleet must update to support 8.33 kHz (it is assumed that AT class aircraft
have already converted to 8.33 kHz).
24
These are illustrative figures, believed by the study team to be realistic. The figures
have not been validated by NATS.
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