It's odd that so many have said that we need crosses that are from a position near the byline, when that is what most strikers need. However, I think what made Andy great in the air was that he could take a cross from a very deep position and use his neck and still make it a great header. That's what he did at Newcastle; go back and watch the videos and there are several great goals where the cross comes in from 20 yards deep or so, at a diagonal.
He still needs it to come in at pace, obviously more so if it's coming from that angle, but he has fantastic technique to whip his neck around and get good placement on the shot. Look at the goal he scored for us last season against City, with Enrique's (I think? or was it Meireles?) ball in coming from at least 25 yards from the byline, and he just gets up to it and glances it into the corner. Fantastic header, and he's capable of them.
If he's only capable of getting good power when the ball comes back at him from the byline, then there's nothing special about his heading ability at all. Half the strikers in this league can do that. It's Andy's ability to make something of a "half-decent" or even marginal ball that makes him good in the air. Or did, at least, until he transferred here.