Hi all,How is the headwind component of a crosswing calculated for Vref or Vapp? Thanks,Christos

It pretty much has no effect. Either with no wind, or a 20 knot headwind, you are still going the same airspeed, putting the same amount of air over the wings. The thing that changes is the groundspeed. If you land at 140 knots with no wind, you touch down at 140 knots, but if you have a 20 knot headwind, you land at 120 knots groundspeed.The equation for all of this is...0.5*(("Approach Airspeed"+"Head/Tailwind")*1.6878)*((("Approach Airspeed"+"Head/Tailwind")*1.6878)/"Autobrake Decellaration Rate")+1000 ^Glideslope is 1000 feet beyond threashold.

Vapp = Vref + correctionCorrection = half hw component + full hw gust component, min 5kt , max 20ktHeadwind component:

 	|\  hw    |a\ wind speed 	|__\	xwa = angle between runway and wind directionHigh School trignometrycos a = hw / wind spdhw = wind spd * cos a

Sample problem

Runway heading 340Wind reported at 300/10-20Vref = 130ktAngle btn Runway and Wind, 'a' = 40degSteady Wind Speed, 'w1' = 10ktGust Component, 'w2' = 20kt - w1 					= 20kt - 10kt 					= 10ktSteady HW component = w1 * cos a                    = 10 * cos 40                    = 8ktGust HW component = w2 * cos a                  = 10 * cos 40                  = 8ktVapp = Vref + 1/2 (Steady HW Component) + Gust HW Component 	= 130kt + (8kt / 2) + 8kt 	= 130kt + 4kt + 8kt 	= 142kt

Hope that helps!Nick Jones

Thanks asdf987, very good.This was exactly what I needed.Happy landings!Christos

Great stuff asdf987.

I quickly wrote a wind component calculator for the people who are too lazy to do the calcs on the fly.http://s000.tinyupload.com/index.php?file_id=13858586255180623145&gk=hyip

This is helpful as well http://www.paragonair.com/public/aircraft/calc_crosswind.html

Actually, in the FMC of the 744X both crosswind and tail/headwind components are shown. I think is page 2 of the Progress menu. I don´t know about the others PMDG planes.

Felipe,We need to consider approach winds, rather than the cruise winds that would be displayed in the progress page, as we set up the arrival prior to top of descent.Cheers,Nick Jones