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Old 16th October 2001 | 19:08
  #6 (permalink)  
Manflex55
 
Joined: Jun 2001
Posts: 927
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From: France & UK
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Let's see...

WS is the variation in direction &/or spd of the local wind, with changes in ht & horizontal distance. It can (usually) B detected by monitoring the ASI: any sudden IAS change could B a WS indication

WS can B associated with :

- gust fronts associated with TS

- wet or dry microbursts (highly concentrated powerful downdraughts). They last from 1 to 5mn & may reach a peak intensity of 45kt (hence a difference in horizontal spd of as much as 90kt)

- frontal passage, especially when the spd of the front is 30kt or more. With the normal easterly trk of a depression, the danger areas for WS are both ahead of the warm front & behind the cold front (the latter being the most dangerous)

- low lvl inversions : @ night in SKC conditions, the sfc cools very quickly to quite low T° & the sfc W/V drops to calm (or light & VRB), whereas, above the sfc, the wind can B quite strong. This difference produces a shallow transitional lyr marked by an inversion & WS

- topographical factors, interrupting the flow around terminal areas (buildings, mountains...)

- lee wave rotors, associated with mountain waves, which produce both vertical & horizontal WS


On approach to land (or on clb after TO), the effects of WS depend on the headwind resultant:

* With a sudden DECREASE in headwind (or increase in tailwind), IAS, lift & pitch all DECREASE, causing your ROD to INCREASE => tendency to go under the glide path => some pwr should B added to compensate.

* With a sudden INCREASE in headwind (or decrease in tailwind), IAS, lift & pitch all INCREASE, causing your ROD to DECREASE => tendency to go above the glide path => need to reduce pwr a bit to compensate.

Basically, keep your hand on the throttles & the ASI within your scan.

MF
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