MET.TR.210 Observing meteorological elements

HUMAN OBSERVATION Observers at an aerodrome should be located, as far as practical, so as to provide data which is representative of the area for which the observations are required.

HUMAN OBSERVATION When a semi-automatic observing system is used, the observer should be located, as far as practical, so as to supply data which is representative of the area for which the observations are required.

OPERATIONALLY DESIRABLE ACCURACY OF OBSERVATION

SURFACE WIND

(a)When local routine report and local special report are used for departing or arriving aircraft, the surface wind observations for these reports should be representative of conditions along the runway or the touchdown zone respectively.

(b)For METAR and SPECI, the surface wind observations should be representative of the conditions above the whole runway where there is only one runway, and the whole runway complex where there is more than one runway.

SURFACE WIND — TAKE-OFF AND LANDING Since, in practice, the surface wind cannot be measured directly on the runway, surface wind observations for take-off and landing are expected to be the best practicable indication of the winds which an aircraft will encounter during take-off and landing.

SURFACE WIND — SITING

(a)Reported surface wind should be representative of a wind at a height of 30 ± 3 ft (10 ± 1 m) above the ground.

(b)Representative surface wind observations should be obtained by the use of sensors appropriately sited.

(c)Sensors for surface wind observations for local routine report and local special report should be sited to give the best practicable indication of conditions along the runway and touchdown zones.

(d)At aerodromes where topography or prevalent weather conditions cause significant differences in surface wind at various sections of the runway, additional sensors should be provided.

SURFACE WIND — SITING Specifications concerning the siting of equipment and installations on operational areas, aiming at reducing the hazard to aircraft to a minimum, are contained in the EASA CS ADR-DSN.T.915 ‘Siting of equipment and installations on operational areas’.

SURFACE WIND — DISPLAY The mean values of, and significant variations in, the surface wind direction and speed for each sensor should be derived and displayed by automated equipment.

SURFACE WIND — AVERAGING The averaging period for measuring variations from the mean wind speed (gusts) reported in accordance with MET.TR.205(a)(3)(iii) should be 3 seconds for local routine report, local special report, METAR, SPECI, and for wind displays used for depicting variations from the mean wind speed (gusts) in ATS units.

SURFACE WIND — AVERAGING — MARKED DISCONTINUITY A marked discontinuity occurs when there is an abrupt and sustained change in wind direction of 30° or more, with a wind speed of 10 kt before or after the change, or a change in wind speed of 10 kt or more, lasting at least 2 minutes.

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 and SPECI, the visibility observations should be representative of the aerodrome.

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.

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.

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.

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.

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’.

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.

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 and SPECI, the RVR should be based on the maximum light intensity available on the runway.

RUNWAY VISUAL RANGE (RVR) — USE OF INSTRUMENTED SYSTEMS

(a)Since accuracy can vary from one instrument design to another, performance characteristics are to be checked before selecting an instrument for assessing the runway visual range.

(b)The calibration of a forward-scatter meter has to be traceable and verifiable to a transmissometer standard, whose accuracy has been verified over the intended operational range.

(c)Guidance on the use of transmissometers and forward-scatter meters in instrumented Runway Visual Range systems is given in ICAO Doc 9328 'Manual of Runway Visual Range Observing and Reporting Practices'.

RUNWAY VISUAL RANGE (RVR) Instrumented systems based on transmissometer or forward-scatter meters must be used to assess RVR on runways intended for Categories II and III instrument approach and landing operations. For Category I instrument approach, other means to assess RVR exist and the assessment of RVR by means of instrumented systems based on transmissometer or forward-scatter meters are therefore not required. However, if the competent authority considers that an instrument system is required at certain aerodromes, it may decide so. Therefore, the requirement in MET.TR.210(c)(2) provides this option, which is consistent with the ICAO Annex 3 approach.

RUNWAY VISUAL RANGE (RVR) — AVERAGING A marked discontinuity occurs when there is an abrupt and sustained change in RVR, lasting at least 2 minutes, which reaches or passes through the values 800, 550, 300 and 175 m.

PRESENT WEATHER — GENERAL

(a)For local routine report and local special report, the present weather information should be representative of the conditions at the aerodrome.

(b)For METAR and SPECI, the present weather information should be representative of the conditions at the aerodrome and, for certain specified present weather phenomena, in its vicinity.

PRESENT WEATHER — SITING When instrumented systems are used for observing present weather phenomena listed under AMC2 MET.TR.205(d), MET.TR.205(d)(3) and AMC1 MET.TR.205(d)(3), representative information should be obtained by the use of sensors appropriately sited.

CLOUDS — GENERAL

(a)Cloud observations for local routine report and local special report should be representative of the runway threshold(s) in use.

(b)Cloud observations for METAR and SPECI should be representative of the aerodrome and its vicinity.

CLOUDS — SITING

(a)When instrumented systems are used for the measurement of the cloud amount and the height of cloud base, representative observations should be obtained by the use of sensors appropriately sited.

(b)For local routine report and local special report, in the case of aerodromes with precision approach runways, sensors for cloud amount and height of cloud base should be sited to give the best practicable indications of the cloud amount and height of cloud base at the threshold of the runway in use. For that purpose, a sensor should be installed at a distance of less than 4 000 ft (1 200 m) before the landing threshold.

AIR TEMPERATURE AND DEW-POINT TEMPERATURE Observations of air temperature and dew-point temperature for local routine report, local special report, METAR and SPECI, should be representative of the whole runway complex.

ATMOSPHERIC PRESSURE — REFERENCE LEVEL

(a)The reference level for the computation of QFE should be the aerodrome elevation.

(b)For non-precision approach runways, whose thresholds are 7 ft (2 m) or more below the aerodrome elevation, and for precision approach runways, the QFE, if required, should refer to the relevant threshold elevation.