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ACP-WGF20/WP -15
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International Civil Aviation Organization
WORKING PAPER / ACP-WGF20/WP-15
11/03/09

AERONAUTICAL COMMUNICATIONS PANEL (ACP)

20TH MEETING OF WORKING GROUP F

Montreal, Canada 24 March – 3 April 2009

Agenda Item 9: / Any Other Business

On a High Percentage of Occasions Definition

(Presented by John Mettrop)

SUMMARY
This paper highlights an issue with the meaning of “On a High Percentage of Occasions” which is currently being debated in the European Frequency Management Group (FMG) as part of it’s review of VHF planning rules.
ACTION
The ACP WG-F is requested to provide it’s opinion on how “ On a High Percentage of Occasions” as contained in Annex 10 Volume III Part 2 should be interpreted.

1.INTRODUCTION

1.1Currently within Europe the planning criteria for VHF communications systems are based for circular services on a 5 to 1 separation standard and for Area services on radio horizon. Whilst the expansion of 8.33 kHz will ease the current congestion, predictions indicate that even a total implementation of 8.33 kHz channel spacing will not be sufficient to avoid congestion prior to the introduction of digital voice services

1.2As part of the cost benefit analysis for the introduction of 8.33 kHz channel spacing below flight level 195 an audit has been started of VHF communications services and the operational justification for those services. The initial audit concentrated on the core States of Europe and one of the recommendations was that the current planning rules be reviewed. This mirrored a decision already taken by the FMG to carryout a review of VHF communications planning rules.

2.discussion

2.1ICAO Annex 10 Volume V in para 4.1.5.1 recommends to use a planning criteria of either a 14 or 20dB D/U ratio, noting that the 20 dB D/U ratio could be interpreted as a 10 to 1 distance ratio.

2.2In order to maximise the capacity Europe is looking to use a 14 dB D/U ratio for all services. However in order to ensure the level of protection required, as well as to avoid mute lift, the signal level at the edge of the service volume and the minimum receiver sensitivity need to be known. The provisions of Annex 10 Volume III with respect to the required performance of the airborne/ground receiver/transmitters are shown below:-

Ground Transmitter

Recommendation.- On a high percentage of occasions, the effective radiated power should be such as to provide a field strength of at least 75 microvolts per metre (minus 109 dBW/m2) within the defined operational coverage of the facility, on the basis of free space propagation

Ground Receiver

Sensitivity. After due allowance has been made for feeder loss and antenna polar diagram variation, the sensitivity of the receiving function shall be such as to provide on a high percentage of occasions an audio output signal with a wanted/unwanted ratio of 15 dB, with a 50 per cent amplitude modulated (A3E) radio signal having a field strength of 20 microvolts per metre (minus 120 dBW/m2) or more.

Airborne Receiver

Recommendation.- After due allowance has been made for aircraft feeder mismatch, attenuation loss and antenna polar diagram variation, the sensitivity of the receiving function shall be such as to provide on a high percentage of occasions an audio output signal with a wanted/unwanted ratio of 15 dB, with a 50 per cent amplitude modulated (A3E) radio signal having a field strength of 75 microvolts per metre (minus 109 dBW/m2)

Airborne Transmitter

Power On a high percentage of occasions, the effective radiated power shalld be such as to provide a field strength of at least 20 microvolts per metre (minus 120 dBW/m2) on the basis of free space propagation, at ranges and altitudes appropriate to the operational conditions pertaining to the areas over which the aircraft is operated.

2.3Whilst all of these provisions provide an absolute value this value is qualified by the statement “on a high percentage of occasions”. This raises the question as to how to interpret the value. Annex 10, Volume V, Attachment A, Para 2 would suggest that “on a high percentage of occasions” should be interpreted as the 95 percentile however WG-F’s opinion is sought as to whether this is the correct interpretation and if not what the correct interpretation should be.

3.ACTION BY THE MEETING

3.1The ACP WGF is requested to clarify the position as to how “on a high percentage of occasions” as contained in Annex 10, Volume III, Part 2 should be interpreted.