International Civil Aviation Organization
Aeronautical Mobile Communication Panel
Working Group-F (AMCP-WGF/7) Meeting
Bangkok, Thailand, 19-27 November 2001
Agenda Item 2: Review of ITU Working Parties and task groups (8B etc…)
AERONAUTICAL MOBILE COMMUNICATIONS PANEL
Working Group F Meeting No.7
Bangkok, Thailand
19- 27 November 2001
How to deal with quantitative arguments with threats on aviation radar
spectrum (and onto other ”safety of life” aeronautical services) coming from
non aeronautical services
Presented by Alain DELRIEU, France
1.Context: recent developments the last WP 8B (22/10-2/11 at
Geneva)
EUROCONTROL presented the results of the Study of the impact on radar
performance of interference coming from radio services other than aviation-related,
on the basis of measurements made on an Austrian airport TMA radar, by the
Technical University of Gratz.
The trigger for this study is to revisit the ITU resolution(s) ( ITU M.1461, 62, 63), the
purpose of which is to protect radar services used in safety of life applications from
external interference, including by limiting the ratio I/N, of the radar-external
interference to the thermal noise at its receiver input. In the first release of this
resolution, adopted recently, a limit of –6dB has been set , without too much
analysis. Accordingly many have argued, and most notably ICAO, that a limit of –
6dB is not adequate, considering that in other circumstances the Radio Reg
specify margins of 10 dB or more to be used for the protection of “safety of life “
services.
The EUROCONTROL study is based on the a-posteriori analysis of a large sample
of radar returns (plots and/or tracks) and has shown that already with an I/N ratio of
–12 dB appreciable losses of air-traffic can be observed.
2. Discussion
This study’s conclusions has been received with mixed reactions, in particular from
those ITU delegates representing radio frequency agencies, including European
ones. These delegates say they are no longer willing to accept “safety of life” claims
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simply on their face value and would like to be presented with more quantifiable data
and criteria associated radar performance degradation.
Obviously the aviation community may not feel as conformable as the
telecommunications community - from which many radio regulator originate- in
putting forward interference-induced radio performance analysis , with results
expressed in classical terms of dB losses, etc…But it has an obligation to present as
forcefully as possible the impact of any abnormal CNS situation in terms of safety
degradation, and associated risk to the travelling public. Additionally because ATS
operators, under safety-impaired conditions must implement contingency measures
and/or procedures to restore safety in accordance to a predefined target by drastic
reductions of the incoming air-traffic flow if required, economic impact of CNS
degradation can also be assessed.
To achieve such an objective the task is then to establish a suitable correlation
between, on one side, a set of technical performance indicators, such as S/N or I/Ns,
falling below pre-established thresholds, criteria, etc… and on the other, operational
risk assessments , e.g. risk of aircraft collisions, as well as economic indicators, e.g.
cost to a national economy when that nation’s busiest airports see even a small
reduction of air-traffic due to accidental or permanent CNS impairments.
It is not an easy task. Moreover some members of the aviation community may
argue that there is an obvious danger if it succeeds:
a) knowledge of the aviation-established acceptability criteria in ITU fora might be
reused to their advantage by those ITU parties “hostile” to aviation in putting
forward more forceful arguments and analysis in favour of band sharing with non
aviation services, at the cost of increased interference to “safety of life” services,
they would be in the position to present as “acceptable” .
b) economic ressources those “hostile” parties are able to rally can literally “dwarf”
that of aviation’s ; on paper at least those massive economic resources could be
employed to offset the above-mentioned negative economic impact , once it has
been properly assessed.
Another view is that if the aviation community is not proactive enough in attempting to
progress such an impact quantification task, others will do it, resulting for aviation
into the inherent risk of coming unprepared to ITU fora and being confronted with
spectrum sharing proposals adverse to its interests.
3. conclusion
The meeting is invited to comment on the issue raised by this paper, i.e. whether or
not the aviation community must be proactive in developing a quantification
methodology for assessing the impact of CNS performance degradation due to
radio interference first and beyond to forced spectrum sharing as may come with
future WRC decisions, at minimum in units defining risk to safety of life and economic
impact at a national level.
On the practical side, an informal “radar interference” group has been set up in WP
8B comprising both aviation and telecommunication communities representatives, the
aviation members of which are invited to act with better co-ordination among
themselves.
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