Dick,
You ought not to arithmetically average vector quantities like wind direction and strength
I don't have my Trevor Thom books with me, so I can't swear to this, but I'm sure the technique that the books teach for PPL is to use a weighted average of adjacent wind directions and speed from form 214 - it's certainly a technique which I use quite regularly when I'm flight planning. Why do you say you should not do this?
Have to admit that I don't remember being asked to average wind vectors for the ATPL exams.
FFF
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