How high can a chicken fly?

[bills]

I have 6 sex-links that are approx. 25 weeks old. I keep them in a roofed enclosed run, and for the most part seem very happy. I have a large unroofed outer run, that is six feet high. I have been tempted to let them into this larger run, when I am working in the back yard, just to give them a little more free range. My fear is they may fly over the fence, and then they wouldn't be able to get back to the coop, for egg lating, feed or water. As well they would be subject to predators. (Lots of cats & bald eagles around)

Can a sex-link chicken fly over a six foot fence?

 

[Red]

Our BSL hen has flown into a 6ft conifer tree before, but she is fairly slim and light. Our other BSL hen is quite heavy and can't fly more than a few feet