Originally Posted by
grahammcfadyen
Hi James,
Boeing stipulates medium runway conditions (runways saturated with heavy rain) max cross wind factor 25 knots.
Example: Approaching Glasgow Airport using the Lanark 1 ALPHA approach flying a Boeing 737-800
1/ (ATIS reports wind 275/G35-55) captain decides ILS 23 approach giving an offset angle of 40 degrees.
2/ Mean wind = 45 knots.
3/ Approximate calculation using the "sine" of 40 degrees is 0.7.
4/ Multiply 0.7 by mean wind 45 knots = 31 knots.
5/ Compare the actual cross wind factor against the manufacturers stipulated maximum cross wind factor.
Clearly the actual cross wind factor in this example exceeds the manufacturers cross wind limitations of 25 knots for medium condition runways.
6/ Scottish control advises descend to FL50 heading 300 reduce speed 250 knots. Then descend to 2300 feet QNH 1015 cleared for the ILS 23 report localizer
established.
7/ Captain at this stage requests an up to date wind report.
8/ Captain reports localizer established.
9/ Scottish control advises wind increasing 275 gusting 45 to 65 knots
10/ Captain then goes back to his rough mental cross wind calculations and obviously decides to divert.
11/ Captain requests to Scottish control; "request missed approach procedure to holding pattern so to permit time enough to decide best alternative airport?"
Formula. The crosswind component is equal to the speed (V) of the wind multiplied by the sine of the angular difference (XWC = V × Sine ). Therefore, in the example given above (Rwy 21 – W/V 240/20) the angular difference is 30 degrees, and the sine of 30 degrees is 0.5.
Hope this information has been of some use and best of luck for the future.
Graham McFadyen
Oh FFS - you clearly have never flown a commercial airplane...........