What makes ATC fly AI tailwind on Take Off?

[Guest Keyno-onyeK]

About 50% of the time i find airports do not activate take off runways into headwind. I checked the AFCAD, and rechecked the ATIS and weather(ASV6) and i can't figure out why.For example..KEWR 212@8, but ATC directs you to take off 4L, instead of 22R. Theres surface wind, and winds aloft, is there another that directing ATC to T/O against Pilots wishes? Any clues or help would be great. thanksKeyno

[RFields5421 1]

The FAA and FS use the concept of preferred runways and light and variable winds.Most of the time in FS you need more than 10 kts wind to turn a runway away from a preferred runway direction in FS.In the real world turning an airport like KEWR is a lengthy complicated task and has to be coordinated to ensure changing landing and takeoff patterns don't have a negative impact upon traffic at other airports it the area.The decision of landing / taking off with a light tailwind is made more on traffic patterns at busy airports than the weather.

[mgh 89]

Similar rules apply in the UK. At Heathrow the limiting tailwind component is 5kt though and applies if the runway is dry.

[Guest Keyno-onyeK]

Ahh that helps in understanding, need 10+ winds to change preferred T/O RWY.thanks