3.3.3 The requirements are as follows:
3.3.3.1 The mean direction and the mean speed of the surface wind is to be measured (51), as well as significant variations of the wind direction and speed (52). Since, in practice, it is difficult to measure the surface wind directly on the runway, surface wind observations for take-off and landing should be the best practicable indication of the winds that an aircraft will encounter during take-off and landing (53).
3.3.3.2 For reports for take-off, the surface wind observations are to be representative of conditions along the runway (54), and for reports for landing the observations are to be representative of the touchdown zone (55). Surface wind sensors for take-off and landing shall be positioned to represent the wind flow at between 6 m to 10 m (20-30 ft) above the runway (56). No corrections to the speed measurements are required for sensors positioned between 5 m and 7 m above the runway. The minimum acceptable height for the primary wind sensor is 5 metres (2256).
For METAR reports sensors shall be positioned to represent the wind flow at 10 m (20-30 ft) above the whole runway where there is only one runway and the runway complex where there is more than one runway (57). The minimum acceptable height for the primary wind sensors is 5 m (2256).
3.3.3.3 Representative surface wind observations are to be obtained by the use of sensors appropriately sited as determined by local conditions (58). Sensors for surface wind observations for reports for take-off and landing are to be sited to give the best practicable indication of conditions along the runway (e.g. lift-off and touchdown zones) (59). At aerodromes where the topography or prevalent weather conditions cause significant differences in surface wind at various sections of the runway, additional sensors are to be provided (60).
3.3.3.4 Surface wind indicators relating to each sensor shall be located in the appropriate air traffic services unit (61). Where separate sensors are required as specified above the indicators shall be clearly marked to identify the runway and section of runway monitored by each sensor (62).
3.3.3.5 The sensor giving the best practicable indication of the surface wind at the touchdown point shall be used for all reports for take-off and landing (63). If this sensor does not give representative winds along the whole length of the runway then the indications from other sensors may be passed when requested by the pilot or when considered appropriate by the controller. Providers are to determine which sensors should be used for each runway or runway section (64).
3.3.3.6 The averaging period for wind observations shall be:
a) two minutes for reports used at the aerodrome for take-off and landing and for wind indicators in air traffic service units (65). The instantaneous surface wind should be available to be given to pilots on request particularly at aerodromes supporting primarily the operations of aircraft whose maximum total weight authorised is 5,700 kg or less (66).
b) ten minutes for METAR reports except that when the 10-minute period includes a marked discontinuity in the wind direction and/or speed, only data occurring since the discontinuity is to be used for obtaining mean values, hence the time interval in these circumstances are to be correspondingly reduced (67).
NOTE: Further guidance in relation to METAR reports is contained in CAP 746, Chapter 4.
3.3.3.7 In reports for take-off and landing, variations in the wind direction shall be given when the total variation is 60° or more with mean speeds above 6 km/h (3 kt) (68); such directional variations shall be expressed as the two extreme directions between which the wind has varied during the past 10 minutes (69). Variations from the mean wind speed (gusts) during the past 10 minutes shall be reported only when the variation from the mean speed has exceeded 20 km/h (10kt) or more (70); such speed variations (gusts) shall be expressed as the maximum and minimum speeds attained (71). When the ten-minute period includes a marked discontinuity in the wind direction and/or speed, only variations in the direction and speed occurring since the discontinuity are to be reported (72). The variations in direction and speed are to be derived:
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本文链接地址：CAP 670 Air Traffic Services Safety Requirements 2(106)
