Page 129 - UK ATM ANS Regulations (Consolidated) 201121

Part MET - ANNEX V - Specific Requirements for the Providers of Meteorological
Services

or more, with a wind speed of 10 kt (5 m/s) before or after the change, or a change in wind speed of
10 kt (5 m/s) or more, lasting at least 2 minutes.
MET.TR.210(b)(1) AMC1 Observing meteorological elements
VISIBILITY - GENERAL
(a) When instrumented systems are used for the measurement of visibility, their output
should be updated at least every 60 seconds to permit provision of current representative
values.
(b) When instrumented systems are used for the measurement of visibility, it should be
measured at a height of approximately 7.5 ft (2.5 m) above the runway.
(c) When local routine report and local special report are used for departing aircraft, the
visibility observations for these reports should be representative of the conditions along
the runway.
(d) When local routine report and local special report are used for arriving aircraft, the visibility
observations for these reports should be representative of the touchdown zone of the
runway.
(e) For METAR, the visibility observations should be representative of the aerodrome.
MET.TR.210(b)(2) AMC1 Observing meteorological elements
VISIBILITY - SITING
(a) When instrumented systems are used for the measurement of visibility, representative
visibility observations should be obtained by the use of sensors appropriately sited.
(b) Sensors for visibility observations for local routine reports and local special reports should
be sited to give the best practicable indications of visibility along the runway and
touchdown zone.
MET.TR.210(b)(4) AMC1 Observing meteorological elements
VISIBILITY - AVERAGING
The averaging period for visibility should be 1 minute for local routine reports and local special reports
and for visibility displays in ATS units.
MET.TR.210(b)(4) GM1 Observing meteorological elements
VISIBILITY - AVERAGING - MARKED DISCONTINUITY
A marked discontinuity occurs when there is an abrupt and sustained change in visibility, lasting at
least 2 minutes, which reaches or passes through one or more of the following values: 800, 1 500 or
3 000 and, in cases where significant numbers of flights are operated in accordance with the visual
flight rules, 5 000 m.
MET.TR.210(c) AMC1 Observing meteorological elements
RUNWAY VISUAL RANGE (RVR) - ASSESSMENT
RVR should be assessed:
(a) at a height of approximately 7.5 ft (2.5 m) above the runway for instrument systems or at
a height of approximately 15 ft (5 m) above the runway by a human observer;
(b) at a lateral distance from the runway centre line of not more than 120 m.
MET.TR.210(c) GM1 Observing meteorological elements
RUNWAY VISUAL RANGE (RVR) ASSESSMENT
A detailed understanding of the assessment of RVR is described in ICAO Doc 9328 'Manual on 'RVR
- Observing and reporting practices'.
MET.TR.210(c)(1) AMC1 Observing meteorological elements
RUNWAY VISUAL RANGE (RVR) - SITING
(a) The site for observations to be representative of the touchdown zone should be located
about 300 m along the runway from the threshold.
(b) The sites for observations to be representative of the mid-point and stop-end of the
runway should be located at a distance of 1 000 to 1 500 m along the runway from the
threshold and at a distance of about 300 m from the other end of the runway.
(c) The exact position of these sites and, if necessary, additional sites should be decided
after considering aeronautical, meteorological and climatological factors such as long
runways, swamps and other fog-prone areas.
MET.TR.210(c)(2) AMC1 Observing meteorological elements
RUNWAY VISUAL RANGE (RVR) - RUNWAY LIGHT INTENSITY
(a) Instrumented systems should consider the runway light intensity.
(b) When instrumented systems are used for the assessment of RVR, computations should
be made separately for each available runway.
(c) For local routine report and local special report, the light intensity to be used for the
computation should be:
(1) for a runway with the lights switched on and a light intensity of more than 3 % of the
maximum light intensity available, the light intensity actually in use on that runway;
(2) for a runway with the lights switched on and a light intensity of 3 % or less of the
maximum light intensity available, the optimum light intensity that would be
appropriate for operational use in the prevailing conditions; and
(3) for a runway with lights switched off (or at the lowest setting pending the
resumption of operations), the optimum light intensity that would be appropriate for
operational use in the prevailing conditions.
(d) In METAR, the RVR should be based on the maximum light intensity available on the
runway.
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